Increasing Solar Efficiency of Cztse Solar Cells Prepared by the Reduction of the Recombination Defects at Cds/Cztse Interface and Post-Deposition Treatment of Cztse with Alkalis

Earth-abundant copper-zinc-tin-chalcogenide kesterites, Cu2ZnSn(S,Se)4, have been examined as most potential alternatives for the leading technologies. However, fabricating low-cost and high-efficiency Cu2ZnSnSe4 (CZTSe) solar cells prepared by electrodeposited metal precursors followed by selenization, facing the most important issues to be solved, are too low open circuit voltage and fill factor. The open circuit voltage of CZTSe solar cells is 600mV (Voc deficit = Eg/q-Voc), while the open circuit voltage of CIGS solar cells is as low as about 400mV, indicating that the open circuit voltage of CZTSe solar cells has greatly improved space. Our research team used pulse-current electrodeposited metal precursor and selenization with a low selenium pressure vapor to make CZTSe solar cells with the highest efficiency up to 8.6%. For our prepared CZTSe films, the ratio of Cu/(Zn+Sn) is about 0.8 and the ratio of Zn/Sn is about 1.2. Post deposition treatment with Alkali metal was not used, and potassium hydride etching or other surface treatment to the absorption layer was not used. Cadmium sulfide was deposited by a conventional method. Therefore, the project will improve the open circuit voltage and fill factor for the improvement of technologies that have not been used in the past. Based on our previous study, the optimal CdS buffer layer process is proposed to reduce the interfacial recombination at CdS/CZTSe interface. The main research topics are as follows: 1. Observe the effect of Cu-doped CdS film and its thickness on cell performance. 2. Study the impact of the different CdS deposition approaches on cell performance for preparing CdS films synthesized by changing the Cd source (nitrate Cadmium and sulfate Cadmium) and the nominal S/Cd ratio. 3. Compare the effect of Cd2 + treatment on CZTSe film before CdS film deposition for cell performance. 4. Study the effect of indium sulfide/cadmium sulfide stack buffer layers on cell performnce. As for how to reduce the non-radiative recombination of absorption layer, post deposition treatment with alkali will be studied to passivate grain boundary or surface defects in order to increase the open circuit voltage and reduce the series resistance. Through the mentioned-above investigation and based on our previous CZTSe study, we believe that as high as 10 % efficiency of CZTSe solar cells can be achieved

Project ID:PB10708-1951
External Project ID:MOST107-2221-E182-076