Thin film solar cell based on p-CuSbS₂ together with Cd-free GaN/InGaN bilayer

Abstract

CuSbS₂ thin film solar cell with 2.99 % efficiency has been demonstrated by using the Cd-free GaN and In_0.15Ga_0.85N as n-type semiconductor bilayer. CuSbS₂ films on the TiN-coated Mo/glass substrates were made by co-sputtering technique at 300 °C with a cermet target of (Cu + Sb₂S₃) operated at 50–60 W and a metal target of Cu at 2 W, followed by thermal annealing at 350–450 °C for 1 h. The effects of processing conditions on the growth behavior, microstructural characteristics, and electrical properties of CuSbS₂ films had been investigated. Solar cell devices were fabricated by depositing ~50 nm GaN and ~300 nm In_0.15Ga_0.85N layers with low temperature radio-frequency (RF) sputtering method, followed by RF sputtering 300–400 nm indium-tin oxide for front contact and pasting silver glue for electric contacts. The CuSbS₂ thin film sputtered at 55 W had a [Cu]/[Sb] ratio of 0.80 with co-exists of the Sb₂S₃, and had a hole concentration of 1.41 × 10¹⁸ cm⁻³, an electrical conductivity 0.1 S cm⁻¹, and mobility of 13 cm² V⁻¹ s⁻¹. The efficiency of the solar cell device had a 3.83-fold increase if the p-CuSbS₂/CdS/n-ZnO system had its conventionally designed CdS/n-type ZnO layer replaced by n-type GaN/In_0.15Ga_0.85N bilayer.