A solution approach to p-type Cu2FeSnS4 thin-films and pn-junction solar cells: Role of electron selective materials on their performance

We present formation of Cu2FeSnS4 (CFTS) thin-films through successive ionic layer adsorption and reaction (SILAR) method. We have considered a range of chalcogenides as n-type compound semiconductors, also formed through SILAR method, in conjunction with the p-nature of CFTS to fabricate and characterize pn-junction solar cells. The film-deposition method, which is a low temperature and non-vacuum one and is also suitable for obtaining films of large-areas, has maintained a balance between fabrication cost and phase purity. From scanning tunneling spectroscopy and correspondingly density of states of the semiconductors, we have estimated their band-edges to draw energy-level diagram of the devices. This has led in establishing a correlation between the band-alignment in the pn-junctions and energy conversion efficiency of solar cells based on the junctions. The correlation has been further supported by diode parameters of the junctions. An energy conversion efficiency of 2.9% with promising reproducibility could be achieved in CFTS vertical bar Bi2S3 junctions formed through this room-temperature film deposition route.