Band offset at the heterojunction interfaces of CdS/ZnSnP_2, ZnS/ZnSnP_2, and In_2S_3/ZnSnP_2

摘要

Heterojunctions were formed between ZnSnP_2 and buffer materials, CdS, ZnS, and In_2S_3, using chemical bath deposition. The band offset was investigated by X-ray photoelectron spectroscopy based on Kraut method. The conduction band offset, ΔE_C, between ZnSnP_2 and CdS was estimated to be -1.2 eV, which significantly limits the open circuit voltage, V_(OC). Conversely, ΔE_C at the heterojunction between ZnSnP_2 and ZnS was +0.3 eV, which is within the optimal offset range. In the case of In_2S_3, ΔE_C was a relatively small value, -0.2 eV, and In_2S_3 is potentially useful as a buffer layer in ZnSnP_2 solar cells. The J-V characteristics of heterojunction diodes with an Al/sulfides/ ZnSnP_2 bulk/Mo structure also suggested that ZnS and In_2S_3 are promising candidates for buffer layers in ZnSnP_2 thin film solar cells, and the band alignment is a key factor for the higher efficiency of solar cells with heterojunctions.