Towards high-efficiency planar heterojunction antimony sulfide solar cells

Abstract

Recently, antimony sulfide (Sb2S3) based solar cells have received substantial attention, however their practical efficiency is far from ideal. Therefore, it is critical to provide numerical simulation on the devices, giving possible avenues to improve the performance. A planar heterojunction solar cell with a structure of FTO/electron transport layer (ETL)/Sb2S3/Cu2O/Au was investigated theoretically by Solar Cell Capacitance Simulator (SCAPS). The influence of different ETLs (CdS, TiO2, ZnO) and Cu2O layer has been firstly analyzed, and our results show that the best ETL is TiO2, and the device efficiency can be significantly increased when Cu2O is used as a hole transport layer (HTL). Then, the electron affinity of TiO2, Sb2S3 layer thickness, defect density, and metal work function on device performance have also been studied systematically. The best electron affinity of TiO2 is 3.6 eV, because a small positive conduction band offset (ΔEC = 0.1 eV) at the TiO2/Sb2S3 interface can be formed, enhancing carrier transport, and consequently, improving the device performance. Further, the optimal thickness for Sb2S3 layer is 200 nm when the defect density of the Sb2S3 layer is 1015 cm−3. To achieve ideal performance, the defect densities in the Sb2S3 layer and at the Sb2S3 interfaces should be as low as 1012 cm−3 and 2 × 1015 cm−2, respectively. In addition, the work function of the metal electrode larger than 4.9 eV is beneficial to device performance. Finally, a Sb2S3 solar cell with the conversion efficiency of 21.43% can be achieved after optimization, which performance is close to the conventional thin film solar cells. Our simulation results suggest the potential of Sb2S3 solar cells.