Investigation On The Device Fabrication And Photovoltaic Properties Of Sb₂Se₃ Based Solar Cells

The demand for energy is ever increasing with the developmentof social economy and expansion of the world population.Coal,oil and nature gas are major energy resources at present.However,fossil fuel will be finally used up due to the limited storage.It has been widely acknowledged that the use of fossil fuels causesserious environment pollution such as greenhouse effect or haze.In this regard,there is an urgent need for clean energy to alleviate the reliance on the conventional fossil fuels.Among many kinds of green energy resources,solar energy has attracted intense attention owing the ample quantity,clean and easy collection.Solar cell is one of the convenientways to convertsolar energy to electricity.To date,several kinds of solar devices have developed,among which copper Indium Gallium Selenide?Cu₂InGaSe₄,CIGS?thin film solar cell in one of the high performance solar cells that hasreached a record power conversionefficiency 22.3%.This device possesses stable structure and good low light performance and gains quick development.However,it is difficult for widespread applications because of the high cost.There are two reasons responsible for the high cost.One is the cost of CIGS itself since indium and gallium in CIGS is rare elements with a high price.Another one is the difficulty in fabricating CIGS thin film because it is hard to reproducibly obtain quaternary compounds with well-defined stoichiometry.This in turn leads to poor eligibility ratein CIGS solar cell production,which indirectly increases the fabrication cost.To apply solar cells at low cost with high efficiency,researches have made continuous efforts into the development of alternative light absorbing materials.Antimony Selenide?Sb₂Se₃?,as a simple binary material,is a kind suitable semiconducting material for the light absorption in solar cell.The reproducibility is high in the material synthesis because of the simple chemical composition.As a new material for thin film solar cell,the investigation has attracted more and more attention.To obtain high efficiency solar cells based on Sb₂Se₃,we conducted detailed investigation regarding the materials synthesis,device fabrication,characterization and fundamental analysis in this thesis.Firstly,we fabricated Sb₂Se₃ thin film by selenizing metal precursor deposited by sputtering.We studied the morphology,structure and bandgap characteristics of Sb₂Se₃ films under different anneal conditions.We found that Sb₂Se₃ tends tolose when the anneal temperature is too high andthe best condition isanneal at 320?for 20 minutes.However,under traditional anneal process,XRD pattern showed all samples possessing crystal face with high resistance,which brings forth poor performance of solar cell devices.To improve the film quality,we introduced rapid thermal process?RTP?to selenize Sb metal precursor.In this study,we examined different anneal conditions including anneal temperature,anneal time and heating rate.It turns out that the best anneal condition is at 400? for 10 minutes.Finally,we compared the two sets of samples obtained by the above thermal treatment processes.Secondly,we studied interfacial propertiesbetween CdS and Sb₂Se₃.We deposited CdS by Chemical Bath Deposition?CBD?on Sb₂Se₃.Morphology and structure of the as-synthesizedCdS arealso studied in detail.We used XPS to study band alignment of CdS and Sb₂Se₃ and we found that the contact between CdS and Sb₂Se₃ is type ?.In addition,we also used CBD to prepare ZnS thin film as buffer layer in solar cells.The band alignment of ZnS and Sb₂Se₃ is also studied.The contact between ZnS and Sb₂Se₃ is type ?.The results showed both CdS and ZnS can be used as buffer layer in thin film solar cells.Finally,we fabricatedSb₂Se₃ thin film solar cells usingthe same structure as CIGS thin film solar cells.By using CdS as buffer layer,we introduced thermal treatmentto improve contactbetween CdS and Sb₂Se₃.With that,the best solar cell device delivers open circuit voltage of 414mV,short circuit current of 16 mA/cm² and power conversion efficiency of 3.47%.The gap to the best solar cell device reported is also analyzed.