反式钙钛矿太阳电池英文回答：Perovskite solar cells, also known as inverted perovskite solar cells, are a type of solar cell that uses a perovskite-structured compound as the light-harvesting layer. This type of solar cell has gained significant attention in recent years due to its high efficiency and low production cost.One of the key advantages of perovskite solar cells is their high power conversion efficiency. The efficiency of perovskite solar cells has increased rapidly in recent years, with the current record exceeding 25%. This high efficiency is comparable to that of traditional silicon-based solar cells, making perovskite solar cells a promising alternative for solar energy generation.In addition to high efficiency, perovskite solar cells also offer the advantage of low production cost. Thematerials used in perovskite solar cells are abundant and inexpensive, which contributes to the overall cost-effectiveness of this technology. Furthermore, perovskite solar cells can be manufactured using low-temperature processes, reducing energy consumption and production costs.Despite these advantages, perovskite solar cells also face challenges. One of the main challenges is thestability of the perovskite material. Perovskite solarcells are prone to degradation when exposed to moisture and heat, which can limit their long-term performance. Researchers are actively working to improve the stabilityof perovskite solar cells to ensure their reliability and durability.In conclusion, perovskite solar cells offer high efficiency and low production cost, making them a promising technology for solar energy generation. However, challenges related to stability and durability need to be addressedfor their widespread commercialization.中文回答：反式钙钛矿太阳电池，也称为倒置钙钛矿太阳电池，是一种利用钙钛矿结构化合物作为光吸收层的太阳能电池。
Home Sign Up!Explore Community SubmitAll Art Craft Food Games Green Home Kids Life Music Offbeat Outdoors Pets Ride Science Sports Tech My home made solar cell step by stepby alessiof76 on May 3, 2009Table of Contents..............................2............................. intro: My home made solar cell step by step ....................................................................2...................................................................Video .............................................2........................................step 1: Materials you will need ...........................................................4.....................step 2: How to prepare copper ......................................................................4 ..........................................step 3: Cooking the copper ................................................................4................................ step 4: Prepare the cooked copper ...................................................................5 ...........................................step 5: Assemble the cell .............................................................6................................. step 6: Fill and seal the cell ............................................................6 .............................................step 7: Test the cell ......................................................................7.................................... Related Instructables ................................................................7 ............................................. Advertisements ...................................................................7 ................................................ Comments ......................................intro:My home made solar cell step by stepVideoHere is a low power low efficiency photovoltaic cell that you can make you own in the kitchenwith materials from the hardware store.This cell is made from cuprous oxide instead of silicon and you can build a working solar cell in 2 hours to build it i follow this instruction: /scitoys/scitoys/echem/echem2.htmlonstep 1:Materials you will needA sheet of copper flashing from the hardware storeA transparent CD caseElectric wireSodium bicarbonate or Table saltAn electric stovehot gluesolderSheet metal shears for cutting the copper sheetI suggest you visit there are many projects and interesting kitstep 2:How to prepare copperThe first step is to cut a piece of the copper sheeting that is about the size of the burner on the stove. Wash your hands so they don't have any grease or oil on them. Then wash the copper sheet with soap or cleanser to get any oil or grease off of it. Use the sandpaper or wire brush to thoroughly clean the copper sheeting, so that any sulphide or other light corrosion is removed.Next, place the cleaned and dried copper sheet on the burner and turn the burner to its highest setting.step 3:Cooking the coppercook the copper for at least 30 min.As the copper gets hotter, the colors are replaced with a black coating of cupric oxide. This is not the oxide we want, but it will flake off later, showing the reds, oranges, pinks, and purples of the cuprous oxide layer underneath.The last bits of color disappear as the burner starts to glow red.When the burner is glowing red-hot, the sheet of copper will be coated with a black cupric oxide coat. Let it cook for a half an hour, so the black coating will be thick. This is important, since a thick coating will flake off nicely, while a thin coat will stay stuck to the copper.After the half hour of cooking, turn off the burner. Leave the hot copper on the burner to cool slowly. If you cool it too quickly, the black oxide will stay stuck to the copper.step 4:Prepare the cooked copperWhen the copper has cooled to room temperature (this takes about 20 minutes), most of the black oxide will be gone. A light scrubbing with your hands under running water will remove most of the small bits. Resist the temptation to remove all of the black spots by hard scrubbing or by flexing the soft copper. This might damage the delicate red cuprous oxide layer we need to make to solar cell work.When you are finished cleaning the copper should be as in the photostep 5:Assemble the cell Cut another sheet of copper , Solder a wire to each copper plate glue to insulate the solderingglue the plate as in photostep 6:Fill and seal the cellseal the cell and fill it with a solution of baking soda (or cooking salt) and waterstep 7:Test the celltest the cell whit SunlightA note about powermy cell produces 58 microamps at 0.10 volts.Don't expect to light light bulbs or charge batteries with this device. It can be used as a light detector or light meter, but it would take acres of them to power your house.Related InstructablesS.P.R.E.E. (Solar Photovoltaic Renewable Electron Encapsulator), a Compact, Durable, and Portable Solar Energy Generator by charlitron it isrevolutionary:imaginemoving(photovoltaics)to absorb sunlights all the dayon everybuilding byBalkeesmy home madesolar cell (video)by alessiof76Solar Boat Kit ::KidWind Projectby kidwindrobMake a highpowered solarpanel frombroken solarcells bymattfeliceSmall SolarPanel by kinz1jgHow to Make ASolar PoweredFan! by Gjdj3Build a 60 WattSolar Panel bymdavis19Comments50 comments Add Comment view all 80 commentsiminoaru says: Jun 12, 2009. 8:38 AM REPLYalessiof76 says: Jun 12, 2009. 11:17 AM REPLYI hope the translation is correctthanksmaurice1993 says: Jun 1, 2009. 2:55 PM REPLY look, any way of increase the surface area, like in a car radiador? this could increase the amount of light colected by this little cell.you are using a couple of inches squares, but, if you made a beehive, increasing the surface area ny abuot two times or more, the output voltage maybe could be bigger, and, bymirroring the bottom, and maybe making the copper more black, this all could be an efficient increase.( friend, what is copper? what kind of metal is this? I cannot find here in my place:(maurice1993 says: Jun 1, 2009. 3:08 PM REPLY alright, I already discover what is copper, it's 'cobre' round here, sorry my ignorance, I'll try to make one wich the beehive, now I know what to search!I may put some photos, or not?If the photons strike them perpendicular oxide copper have more power and produce more energy, the idea of using a system similar to a hive isbeautiful but difficult to implement, perhaps with a " waved" plate (like VVVVVVV) could work equally requires less work.I found the copper for free on a construction site. It 'used to construct gutters, and there are often leftovers. Your project photos are wellcome!!ciao Alessiodark sponge says: May 4, 2009. 2:57 PM REPLYNow I need to find something I can power with 0.0000058 watts of electricity....alessiof76 says: May 4, 2009. 3:30 PM REPLY The mobile phone of an ant ? ;)dark sponge says: May 5, 2009. 7:02 PM REPLYIt would take 862,069 of them in full sunlight to charge my phone... This seems very useful...Derin says: May 31, 2009. 2:15 AM REPLYLight meter!Derin says: May 31, 2009. 2:00 AM REPLYMaybe for the light meter you could use an op-amp and some MCU's to measure the analog voltage.maurice1993 says: May 5, 2009. 5:29 PM REPLYtry to put this onto a cell phone charger out put, and you will discover a way to produce hydrogen and oxygen!I made this with a margarina(sorry, just forgot the word for this in English) pot, and two clock batteries, each with 1.5 volts and some miliampers. I used waterand salt, 20 cm of wire, and duck tape. when I put the two wires in water, start to make bubbles, two times more in the negative than the positive wire.when I put fire on this little bubbles, they burned like hell!Hey friend, this little thing can be used to energyzer a relay? if so, this could be useful as a light resistor, to control some lights from house, or even outside,by adjusting the resistence of the relay, it'll be propise to control the amount of dark will need to turn the lights on.(of course it'll be need to be off the light uwann to turn on, otherwise, this will be turning on and turning off milhions of times....tacamaral says: May 7, 2009. 7:54 AM REPLY Margarina = Margarine. : )maurice1993 says: May 15, 2009. 5:45 PM REPLYthanks man,trying to get the language soon, to can speak with these embarsings.see you laterbruko says: May 8, 2009. 6:01 AM REPLYdevo dire che il progetto è interessante, ma ottieni una tensione troppo bassagrande! sapevo di non essere il solo italiano su instructablesalessiof76 says: May 8, 2009. 11:20 AM REPLY grazie! ho scoperto che ce ne sono anche altri! hai un buon traduttore on line da consigliarmi? sto' diventando idrofobo con babylon!Non so' se continuare le ricerche su questa cella o con quella di graetz al biossido di titanio e antocianine, molto più performante (dicono), pensa che su un grosso forum italiano, questo progetto ha ottenuto solo 1 commento...Ciaobruko says: May 14, 2009. 9:11 AM REPLYscusa se ti rispondo in ritardoio di solito uso google traduttore, basta che vai nella pagina di google e clicchi in alto su "altro" e trovi il traduttorepieplay says: May 8, 2009 The magazine elektor has posted something similar in their magazine and on their site where it's free to download. They use the Leaf green(Chlorophyll) from fruwill do) TiO2 and polyetyleenglycerol (as binding to make it paste). These are Greener to make, more environment friendly to produce Energy reaches about a little mo silicium./y1piv7wT7wYes9pSKnf38KwbtB_CGvmTrTQ1YP3XmE1SbRyllc7fVlvObLUd5BCJfN2Me6TjXry3JbEChqbkIbhTpOUmKfrT_Bh/N070 PDF is in Dutch, first page bottom right contains some weblinksthanksHere is a funny video that explains how to make a photovoltaic graetzel (?) cell/watch?v=bVwzJEhMmD8fusarol says: May 12, 2009. 6:23 AM REPLY thank you for sharing itsfdev says: May 12, 2009. 6:20 AM REPLY nice experimental & learning projectWilderLust says: May 11, 2009. 2:23 AM REPLY hehe... very nice... this is a fun project that is within just about everyone's reach but teaches quite a lot if you get into it. thank you for sharing it :-)alessiof76 says: May 11, 2009. 1:11 PM REPLY thanksalessiof76 says: May 8, 2009. 11:22 PM REPLY When I wrote graez cellI wanted write graetzel cell forgive meuLTIMA says: May 7, 2009. 11:06 AM REPLY wow, i cant believe the low intelligence of some people that are unable to read. so what if some words are spelt wrong, i can still read it. so stop ragin on someone who has posted something and get instructing yourselves, ignorant peoplepdub420 says: May 8, 2009. 10:28 AM REPLY people who have not posted their own instructables should be slow to make disparaging comments about other's work.alessiof76 says: May 7, 2009. 11:19 AM REPLY Thank you for understanding my translation difficultiydombeef says: May 7, 2009. 12:11 PM (removed by author or community request)froggyman says: May 7, 2009. 1:44 PM REPLY thats why it stops producing a charge when it is out of the sun/light?alessiof76 says: May 7, 2009. 12:38 PM REPLY The saline solution need to close the circuit, if you use electrodes of different material becomes a battery, copper oxide is a semiconductor.the photovoltaics effect was discovered with this kind of cell,In 1905 Albert Einstein public his theory on the effect photovoltaics and lead the Nobel Prize also using this type of reaction as an example dombeef says: May 8, 2009. 5:25 PM REPLY Oh Ok thanks for the infomation!blinkizod says: May 7, 2009. 12:19 PM REPLY cool, very good project, congratulations from Guatemalaalessiof76 says: May 7, 2009. 12:42 PM REPLY Thank you but is not my invention, it is a the last century discovery!I found it on Internet, I have built it and I wanted share itthaks from italyjmcarlin says: May 7, 2009. 9:43 AM REPLY How much baking soda/salt do mix in to the water?alessiof76 says: May 7, 2009. 11:16 AM REPLY is is not critical, more the solution is saturated smaller the internal resistance of the cell, but with so small current with two Small spoons are more than sufficientJohnbars says: May 5, 2009. 10:52 PM REPLY Hi there my friend. Can this power up a small radio or a walkman device? If not, then how big must it be to power up such small devices?Thanks so much....bart416 says: May 7, 2009. 9:47 AM REPLY Really depends on the way the radio is built. An old fashioned radio, very unlikely. New electronic ones without displays, shouldn't be that much of a problem if you hook up a few.alessiof76 says: May 6, 2009. 1:22 PM REPLY Hi ! I have built different cells with different results may be that with different cells in series you can feed a small radio with headphones, there are Graetz cell that you can do at home. they deliver at least 5 to 10 times more voltageand more current ( power).I have not yet built it, i need conductive glass and titanium dioxide, not easy to find near my home.jeffreycb says: May 7, 2009. 2:28 PM REPLY what are these cells that deliver 5 to 10 times more voltage? I want to learn about the different other designs. what is "Graetz cell"Johnbars says: May 7, 2009. 5:35 AM REPLY Thanks This is great info for me!.....more power to you!alessiof76 says: May 7, 2009. 11:11 AM REPLY If I find the material I will try to build even a more powerful Graetz cellthat green guy says: May 5, 2009. 11:01 PM REPLY Does this get weaker over time? Do you ever have to change the water solution on the inside or anything?iBurn says: May 4, 2009. 7:25 PM REPLY Spelled "Cooking" wrong there buddy.alessiof76 says: May 4, 2009. 10:37 PM REPLY opps!..thanks I corrected itSuperjustin18 says: May 5, 2009. 1:29 PM REPLY You spelled "oops" wrong there buddy.lolalessiof76 says: May 5, 2009. 2:16 PM REPLY sorry i was writing in Italian !)Superjustin18 says: May 5, 2009. 6:05 PM REPLY LOL really?iBurn says: May 5, 2009. 3:09 PM REPLYSomeone needs to come up with a universal language...then acutally USE it.alessiof76 says: May 5, 2009. 3:25 PM REPLYNO COMMENTiBurn says: May 5, 2009. 3:28 PM REPLYBut that was a comment...seeing as you have to hit the "post comment" button and all....alessiof76 says: May 5, 2009. 3:39 PM REPLYtry to translate :ma va a studiar che no ti ga altro de mejo da far! ghe ne go do bae de ti, xe quasi mezo boto me so fato un cueo cusi tutto el dì allavoro caga alto che no ti si altro!i speak 4 different idioma (not englis) and you?view all 80 comments/id/My-home-made-solar-cell-1/。
Solar CellIntroductionA solar cell, also known as a photovoltaic cell, is an electrical device that converts sunlight into electricity by the photovoltaic effect. It is a key component in solar panels and plays a crucial role in harnessing solar energy. Solar cells are widely used to generate clean and renewable energy for various applications including residential, commercial, and industrial sectors.Working PrincipleSolar cells are based on the principle of the photovoltaic effect. This effect occurs when certain materials, known as semiconductors, absorb photons from sunlight, which then excite the electrons within the material. The excited electrons create an electric current when they flow through the material. This current can be harnessed and used as a source of electrical energy.Types of Solar CellsThere are several types of solar cells that vary in their material composition and efficiency. The most common types include:1.Monocrystalline Silicon Solar Cells:–These solar cells are made from a single crystal structure, resulting in high efficiency.–They have a uniform dark color and are easily recognizable by their rounded edges.–Monocrystalline solar cells tend to be more expensive due to the manufacturing process.2.Polycrystalline (Multicrystalline) Silicon Solar Cells:–These solar cells are made from multiple crystal structures, which makes them less efficient compared to monocrystalline cells.–They have a bluish color and a granular appearance.–Polycrystalline solar cells are more cost-effective compared to monocrystalline cells.3.Thin-Film Solar Cells:–These solar cells are made by depositing a thin layer of semiconductor material onto a substrate.–Thin-film solar cells are flexible and lightweight, making them suitable for various applications.–They have a lower efficiency compared to crystalline silicon solar cells but are cheaper toproduce.anic Solar Cells:–Also known as organic photovoltaic cells (OPV), these solar cells use organic materials as thesemiconductor.–Organic solar cells have the advantage of being printable and can be manufactured using low-costprocesses.–However, their efficiency is currently lower compared to other types of solar cells.Manufacturing ProcessThe manufacturing process of solar cells involves several steps, including:1.Silicon Production:–The primary material used in most solar cells is silicon, which is obtained through a complex process.–Pure silicon is extracted from silica (SiO2), which is then refined and purified to reach the desiredlevel of purity.2.Wafer Production:–The purified silicon is transformed into solid blocks called ingots.–The ingots are then sliced into thin wafers using a diamond saw.–These wafers serve as the base for the solar cells.3.Doping:–Doping is a process in which impurities are added to the silicon wafer to create a p-n junction, which is necessary for the photovoltaic effect.–The addition of phosphorous or boron atoms introduces extra electrons or electron holes into the silicon structure, respectively.4.Formation of Layers:–Several layers are formed on the surface of the silicon wafer to enhance the solar cell’s efficiency.–These layers include anti-reflective coatings and metal contacts.5.Assembly into Modules:–The individual solar cells are interconnected and assembled into modules or panels.–The modules are then encapsulated to protect the solar cells from environmental factors.Efficiency and LimitationsThe efficiency of a solar cell refers to the percentage of sunlight converted into electrical energy. The efficiency varies depending on the type of solar cell and its manufacturing process. Currently, the most efficient solar cells on the market can achieve efficiencies of over 20%.Solar cells, however, have certain limitations, including:1.Efficiency Drop with Temperature:–Solar cells become less efficient as their temperature increases.–High temperatures can reduce the voltage and current output, lowering the overall performance.2.Dependency on Sunlight:–Solar cells rely on sunlight and their efficiency decreases in cloudy or shaded conditions.–The placement and orientation of solar panels play a crucial role in maximizing energy output.3.Cost:–The initial cost of solar cell production is relatively high, although it has been decreasing inrecent years.–The cost of solar cells is influenced by factors such as material type, manufacturing process, andmarket demand.ApplicationsSolar cells have a wide range of applications, including:1.Residential Solar Power Systems:–Solar panels installed on rooftops can generate electricity for residential use.–Excess energy can be fed back into the grid or stored in batteries for later use.mercial and Industrial Solar Power Systems:–Large-scale solar power plants generate electricity for commercial and industrial applications.–These systems can supply power to factories, offices, and other commercial buildings.3.Portable Solar Chargers:–Solar cells can be used to power handheld devices such as smartphones, tablets, and laptops.–Portable solar chargers provide a convenient and renewable source of energy for outdoor activities.4.Solar Lighting:–Solar cells are used in outdoor lighting systems, including streetlights, garden lights, and pathwaylights.–These systems eliminate the need fortraditional electrical wiring and reduce energyconsumption.5.Space Applications:–Solar cells are extensively used in spaceapplications such as satellites and spacecraft.–In space, solar cells provide the necessary power for various onboard systems and equipment.ConclusionSolar cells are vital components in the generation of clean and renewable energy. They utilize the photovoltaic effect to convert sunlight into electricity, making them an environmentally friendly alternative to traditional energy sources. With advancements in technology and decreasing costs, solar cells are becoming increasingly popular and are expected to play a significant role in meeting our future energy needs.。
Effect of Cu deficiency on the optical properties and electronic structure of CuInSe2 and CuIn0.8Ga0.2Se2 determined by spectroscopic ellipsometrySung-Ho Han, Allen M. Hermann, F. S. Hasoon, H. A. Al-Thani, and D. H. LeviCitation: Appl. Phys. Lett. 85, 576 (2004); doi: 10.1063/1.1776616View online: /10.1063/1.1776616View Table of Contents: /resource/1/APPLAB/v85/i4Published by the American Institute of Physics.Related ArticlesDilute-nitride GaInAsN/GaAs site-controlled pyramidal quantum dotsAppl. Phys. Lett. 99, 181113 (2011)Modifications in structural and electronic properties of TiO2 thin films using swift heavy ion irradiation J. Appl. Phys. 110, 083718 (2011)Point defects in gallium nitride: X-ray absorption measurements and multiple scattering simulations Appl. Phys. Lett. 99, 172107 (2011)Spontaneous polarization and band gap bowing in YxAlyGa1-x-yN alloys lattice-matched to GaNJ. Appl. Phys. 110, 074114 (2011)Band gap and electronic properties of wurtzite-structure ZnO co-doped with IIA and IIIAJ. Appl. Phys. 110, 063724 (2011)Additional information on Appl. Phys. Lett.Journal Homepage: /Journal Information: /about/about_the_journalTop downloads: /features/most_downloadedInformation for Authors: /authorsEffect of Cu deficiency on the optical properties and electronic structure of CuInSe2and CuIn0.8Ga0.2Se2determined by spectroscopic ellipsometry Sung-Ho Han a)and Allen M.HermannDepartment of Physics,University of Colorado,Boulder,Colorado80303-0390F.S.Hasoon,H.A.Al-Thani,and D.H.LeviNational Renewable Energy Laboratory,1617Cole Boulevard,Golden,Colorado80401-3393(Received29March2004;accepted4June2004)Spectroscopic ellipsometry measurements of CuInSe2(CIS)and CuIn0.8Ga0.2Se2(CIGS)reveal thatthere are important differences in electronic properties between stoichiometric CIS(CIGS)andCu-poor CIS(CIGS).Wefind a reduction in the absorption strength in the spectral region of1–3eV.This reduction can be explained in terms of the Cu3d density of states.Cu-poor CIS(CIGS)materials show an increase in band gap due to the reduction in repulsion between Cu3d andSe4p states.The experimental results have important implications for the function ofpolycrystalline optoelectronic devices.©2004American Institute of Physics.[DOI:10.1063/1.1776616]Polycrystalline thin-film chalcopyrite CuIn1−x Ga x Se2 (CIGS)is currently used as an absorber layer for high-efficiency photovoltaic(PV)solar cells.The efficiency of record laboratory polycrystalline thin-film solar cells based on CIGS has reached nearly20%,1while single-crystalline CIGS solar cells have just reached13%.2Electronic struc-tures of CuB III X2VI materials have been thoroughly studied.3–5 High-efficiency polycrystalline solar cells are always slightly Cu deficient,with about23.5–24.5at.%Cu.There have been studies of the optical properties of CIGS materials with different Ga compositions,6–8but considering the fact that high-efficiency PV solar cells use Cu-poor CIGS,it is crucial to study the effect of content on CIGS electronic properties. In this study,through the analysis of the dielectric function, we compare the electronic structure of Cu-poor ͑21.7at.%Cu͒CuInSe2(CIS)films with stoichemetric ͑25.1at.%Cu͒CISfilms.We also compare the electronic structure of slightly Cu-poor͑23.3at.%Cu͒CIGSfilms withstoichiometric͑24.8at.%Cu͒bulk polycrystalline CIGS.CIGS surfaces are inclined to have Cu vacancies.9,10In con-trast to zinc-blende semiconductors,where the nonpolar (110)surface is more stable than all polar surfaces,the chal-copyrite semiconductor CuInSe2has the lowest energy when the surface has the(112)-cation and͑1¯1¯2¯͒-anion polar facets through defect-induced reconstructions.9Previous work has studied electronic and geometric structures of nearly sto-ichiometric bulk and Cu-poor surfaces.4,10,11In contrast,we focus on Cu-poor CIS and CIGS samples where both the surface and bulk regions are Cu poor to probe the properties of Cu-deficient CIS(CIGS)materials.Spectroscopic ellipsometry(SE)is a powerful technique for determining the optical functions of bulk and thin-film materials.Alonso et al.have reported SE measurements of the pseudodielectric functions of single-crystalline CIS and CuGaSe2(CGS),6as well as bulk polycrystalline CIGS alloys.7In those studies,they used a two-phase model to analyze the ellipsometric data.12Such a treatment is not ap-propriate for the analysis of thin-film polycrystalline materi-als used for real-world CIGS solar cells.The polycrystalline thin-film CIS and CIGS samples were deposited onto molybdenum-coated soda-lime glass.The molybdenum thickness was about1.0m.CIS and CIGS layer thick-nesses were about1.2m and2.0m,respectively.These films were grown by the single-stage coevaporation tech-nique,where thefluxes of Cu,In,Ga,and Se were constant during deposition.To accurately determine the optical prop-erties of these multilayer thin-film samples,one must analyze the SE data using a full multilayer model including the ef-fects of the surface roughness and the underlying molybde-num layer.8We have applied these techniques to determine the dielectric functions for several polycrystalline thinfilms of CIS and CIGS alloys.The ellipsometer used to make the measurements in this study is a J.A.Woollam M2000variable-angle spectroscopic ellipsometer,which uses a rotating compensator design.For this work,ellipsometric spectra were measured at angles of incidence of65°,70°,75°,and80°to ensure an accurate determination of the dielectric function of the material,the thicknesses of the material layer,and surface roughness layer.Auger electron spectroscopy(AES)depth profiles showed that the materials have uniform compositions throughout the entire thickness of thefilms.Thicknesses measured by profilometer are in quantitative agreement with those determined by SE.Inductively coupled plasma(ICP) analysis measures the compositions of thin-film CIS and CIGS.Table I provides at.%Cu of thesefilms as determineda)Also with:National Renewable Energy Laboratory,Golden,CO80401; electronic mail:sung-ho.han@ TABLE I.at.%Cu and critical points analyzed by the CPPB model.All samples are polycrytalline.Stoichiometricthin-film CISCu-poorthin-film CISStoichiometricbulk CIGS aSlightlyCu-poorthin-film CIGS at.%Cu25.121.724.823.3E0͑A,B͒ 1.03 1.08 1.11 1.12E0͑C͒ 1.22 1.29 1.33 1.34a Ref.7.APPLIED PHYSICS LETTERS VOLUME85,NUMBER426JULY2004 0003-6951/2004/85(4)/576/3/$20.00©2004American Institute of Physics576by ICP.X-ray diffraction revealed that these films are single phase for stoichemetric thin-film CIS ͑25.1at.%Cu ͒and slightly Cu-poor ͑23.3at.%Cu ͒thin-film CIGS,and mixed phase for Cu-poor ͑21.7at.%Cu ͒thin-film CIS.The CuIn 0.8Ga 0.2Se 2material studied by Alonso et al.also showed uniform chalcopyrite structure with no secondary phases found.7More detailed discussion on the experimental conditions can be found in Ref.8.Figure 1(a )compares the absorption coefficient spectra of stoichemetric and Cu-poor CIS.Figure 1(b )extends this comparison to CIGS materials to generalize the effect of Cu on CIGS materials.Both Figs.1(a )and 1(b )show similar trends.Relative to the stoichiometric samples,absorption de-creases in E 0,E ͑⌫X ͒,and E 1͑A ͒transitions,but increases in the E ͑⌬X ͒transition for Cu-poor materials.The optical tran-sitions in the spectral range of 1–5eV,can be found else-where .6,7Depression of the absorption coefficient is found in Fig.1(a )between stoichiometric ͑24.8at.%Cu ͒thin-film CIS and Cu-poor ͑21.7at.%Cu ͒thin-film CIS in the spec-tral region,1–3eV.Although the band-gap energies are slightly different due to different Ga compositions,Fig.1(b )also shows the depression of absorption coefficient between stoichiometric bulk polycrystalline CuIn 0.8Ga 0.2Se 2and slightly Cu-poor thin-film CIGS with x ϵGa/͑In+Ga ͒=0.18.According to the theoretical calculations of the elec-tronic band structure and density of state (DOS )of the ter-nary chalcopyrite materials by Jaffe and Zunger,3the upper valence band,within 3–4eV of the valence-band maximum (VBM ),is composed primarily of the Cu 3d orbitals,hybrid-ized with the Se-4p orbitals.Several authors have calculated the band structure and DOS of extremely Cu-poor ␥-phase CIS ͑CuIn 5Se 8͒.5Both of these calculations show a reduction of the DOS within 3–4eV of the VBM.Reduction in the DOS of hole states near the VBM should produce a decrease in absorption coefficient near the band edge.This theoretical result is consistent with our experimental observations.Theoretical calculations of CIS band structure predict another effect of Cu deficiency.As stated above,in ternary chalcopyrite CuB III X 2VI ,the upper valence band is composed of Cu 3d and VI 4p state electrons.This was observed ex-perimentally using synchrotron radiation photoemission spectroscopy.13The repulsive p –d interaction pushes the an-tibonding p –d state that constitutes the VBM to higher en-ergies.In the case of Cu-poor CIS and CIGS,the p –d repul-sion is expected to be less than that of stoichiometric materials.The net effect of the decrease in this repulsive interaction would then be a lowering of the VBM.Hence,we expect an increase of the band gap for Cu-poor CIGS.14We analyze the band gap using the critical-point para-bolic band (CPPB )model.14The fitting procedure is done on the calculated second derivative of dielectric function d 2͑͒/d 2,using the method of smoothing polynomials 15to enhance the structure present in the spectra.The structure of the fundamental absorption edge of CuInSe 2is well known.3Considering crystal-field splitting and spin–orbit in-teraction,the three-fold degenerate ⌫15VBM splits into three transitions E 0͑A ͒,E 0͑B ͒,and E 0͑C ͒.The measured critical points are compiled in Table I.In the case of CIS and CuIn 0.8Ga 0.2Se 2,the separation between E 0͑A ͒and E 0͑B ͒cannot be measured because it is below our resolution.7Thus,the structure is composed of the two degenerate peaks,E 0͑A ,B ͒and E 0͑C ͒.E 0͑A ,B ͒and E 0͑C ͒of stoichemetric thin-film CIS 1.03eV and 1.22eV and those of Cu-poor thin-film CIS are 1.08eV and 1.29eV,respectively.We can see that the band gap increases by 0.05eV for Cu-poor CIS.CPs of CIGS materials show trends analogous to those of CIS materials.We compare the dielectric function of bulk polycrystalline stoichiometric ͑24.8at.%Cu ͒CuIn 0.8Ga 0.2Se 2from Alonso et al.7with the dielectric func-tion of slightly Cu-poor ͑23.3at.%Cu ͒thin-film CIGS with x =0.18.E 0͑A ,B ͒,and E 0͑C ͒of bulk stoichiometric CIGS are extracted from the equation with x =0.18in Alonso et al.7According to that calculation,E 0͑A ,B ͒,and E 0͑C ͒of sto-ichiometric bulk CIGS are 1.11eV and 1.33eV,whereas E 0͑A ,B ͒and E 0͑C ͒of slightly Cu-poor thin-film CIGS are 1.12eV and 1.34eV,respectively.We can see that the band gap increases by 0.01eV.This value is smaller than that of CIS due to the smaller difference in the quantities of at.%Cu.Considering our experimental results in the context of the theoretical calculations of the band structure of stoichio-metric and Cu-poor CIS (CIGS ),3–5we have shown that the reduction of the near band-edge absorption coefficient ob-served in Cu-poor CIS (CIGS )is related to a decrease in the density of states near the VBM.This result has important implications for the functioning of high-efficiencypolycrys-FIG.1.(a )Comparison of absorption coefficients between stoichiometric ͑25.1at.%Cu ͒thin-film CIS and Cu-poor thin-film CIS ͑21.7at.%Cu ͒(b ).Comparison of absorption coefficients between stoichiometric ͑24.8at.%Cu ͒bulk polycrystalline CIGS with x =0.2by Alonso et al.(Ref.7)and slightly Cu poor ͑23.3at.%Cu ͒with x =0.18.talline CIGS thin-film the highest.As stated previously,high-est efficiency CIGS PV devices are slightly Cu poor,with23.5–24.5at.%Cu.Theoretical calculations have shown thatthe most energetically favorable surfaces for CIS are the (112)-cation and͑1¯1¯2¯͒-anion polar facets with defect-induced reconstructions producing a layer of Cu vacancies atthe surface.9Numerous experimental measurements haveconfirmed that CIS(CIGS)surfaces are Cu poor.10Becausegrain boundaries(GBs)can be considered as interior sur-faces,it is reasonable to postulate that in the slightly Cu-poorCIGS material used in high-efficiency solar cells,the mate-rial near the GBs is Cu poor,while the grain interiors(GIs)are nearly stoichiometric.4As shown in Ref.4,the reductionof the DOS near the VBM at the GBs effectively produces acharge-neutral barrier to holes.This effectively passivatesthe GBs by only allowing minority-carrier electrons to pen-etrate the GB region.It is known that the GBs act to getterthe defects and impurities in these materials;hence,passiva-tion of the GBs is exceptionally effective in reducing nonra-diative recombination in CIS(CIGS)thin-film solar cells.The Cu-poor materials studied in this letter are significantly more Cu deficient than the materials used in solar cells.It is reasonable to assume that both GIs and GBs are Cu poor in thesefilms.Hence,our measurements of the optical proper-ties and electronic structure reveal the properties of the GB material in an actual solar cell.Hence,these experimental measurements serve as a confirmation of the theoretical cal-culations put forth in Ref.4.The authors thank H.Moutinho for assistance in atomic force microscopy measurements,R.Bhattacharya for assis-tance in ICP measurements,and J.Pankow for assistance in AES profile measurements.The authors acknowledge valu-able discussions with R.Noufiand C.Persson.This work was supported by the U.S.Department of Energy under Con-tract No.DE-AC36-99GO10337.1K.Ramanathan,M.A.Contreras,C.L.Perkins,S.Asher,F.S.Hasoon,J. Keane,D.Young,M.Romero,W.Metzger,R.Noufi,J.Ward,and A. Duda,Prog.Photovoltaics11,225(2003).2C.H.Champness,Proceedings of the29th IEEE Conference(IEEE,Pis-cataway,NJ,2002),p.732;L.S.Yip and I.Shih,Proceedings of the First World Conference on Photovoltaic Energy Conversion(IEEE,Piscataway, NJ,1994),p.210.3J.E.Jaffe and A.Zunger,Phys.Rev.B27,5176(1983);ibid.28,5822 (1983);ibid.29,1882(1984).4C.Persson and A.Zunger,Phys.Rev.Lett.91,266401(2003).5S.B.Zhang,S.-H.Wei,and A.Zunger,Phys.Rev.B57,9642(1998);C. Domain,ribi,S.Taunier,and J.F.Guillemoles,J.Phys.Chem.Solids 64,1657(2003).6M.I.Alonso,K.Wakita,J.Pascual,M.Garriga,and N.Yamamoto,Phys. Rev.B63,075203(2001).7M.I.Alonso,M.Garriga,C.A.Durante Rincön,E.Hernández,and M. León,Appl.Phys.A:Mater.Sci.Process.74,659(2002).8S.-H.Han,D.H.Levi,H.A.Al-Thani,F.S.Hasoon,R.N.Bhattacharya, and A.M.Hermann,Mater.Res.Soc.Symp.Proc.763,B1.8(2003).9J.E.Jaffe and A.Zunger,Phys.Rev.B64,241304(2001);S.B.Zhang and S.-H.Wei,ibid.65,081402(2002);J.E.Jaffe and A.Zunger,J.Phys. Chem.Solids64,1547(2003).10R.Herberholz,U.Rau,H.W.Schock,T.Haalboom,T.Gödecke,F.Ernst, C.Beilharz,K.W.Benz,and D.Cahen,Eur.Phys.J.:Appl.Phys.6,131 (1999);D.Liao and A.Rockett,Appl.Phys.Lett.82,2829(2003).11A.Meeder,L.Weinhardt,R.Stresing,D.Fuertes Marrón,R.Würz,S.M. Babu,T.Schedel-Niedring,M.C.Lux-Steiner,C.Heske,and E.Umbach, J.Phys.Chem.Solids64,1553(2003);I.M.Kötschau and H.W.Schock, ibid.64,1559(2003);J.M.Merino,M.Di Michiel,and M.León,ibid. 64,1649(2003).12R.M.A.Azzam and N.M.Bashara,Ellipsometry and Polarized Light (North-Holland,Amsterdam,1977).13M.Turowski,G.Magaritondo,M.K.Kelly,and R.D.Tomlinson,Phys. Rev.B31,1022(1985).utenschlager,M.Garriga,S.Logothetidis,and M.Cardona,Phys. 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