Calculation of Band Alignment and Interfacial Recombination in CZTS-Based Solar Cell

SOAPS software as a simulation tool was applied to investigate the photovoltaic performance of Cu2Zn4SnS4 (CZTS) thin film solar cells. Firstly, the influence of the work function of back contact on the open circuit voltage (Voc) and efficiency was studied, which increased with the work function and reached the maximum at 5.2 eV. The variation of the efficiency with the conduction band offset (CBO) at CZTS/CdS interface was discussed. The high efficiency of 12% can be obtained when CBO value changed from -0.1 to 0.2 eV, which means a little cliff-like or spike-like band alignment at the CZTS/CdS interface. Under a large spike-like CBO, the efficiency sharply declined because of the large barrier blocking the photo-generated carriers. Furthermore, the recombination and optical electronic characteristics were researched through the insertion of an intermediate layer at absorber/back contact and buffer/absorber interfaces. With the carrier concentration in p+-CZTS intermediate layer inserted at CZTS/Mo interface increasing from 10(15) to 10(18) cm(-3) , the Voc increased from 0.736 V to 0.850 V which promoted the efficiency from 12.03% to 15.60%. By inserting a low doped p(+)-CZTS intermediate layer at CZTS/CdS interface, the efficiency achieved to 17.31%, which is attributed to the low recombination. At the concentration greater than 10(17) cm(-3), the close concentration of electron and hole resulted in the large recombination and inferior performance. The research scheme used in this paper is significant for CZTS-based or other photovoltaic solar cells.