Lifetime, quasi-Fermi level splitting and doping concentration of Cu-rich CuInS2 absorbers

Abstract

Abstract Cu(In,Ga)S2–based solar cells have been shown by Hiroi et al (Hiroi et al 2015 IEEE Journal of Photovoltaics 6 309–312) to achieve higher efficiencies with absorbers processed at high deposition temperatures. Additionally, it is known for CuInS2 cells that the main improvement from higher deposition temperatures is the reduction in the density of deep defects and increased quasi-Fermi level splitting. The increased quasi-Fermi level splitting could result from a reduction in the rate of recombination or from an increase in doping concentration. To investigate which effect is the dominant one, we perform time-resolved photoluminescence measurements and estimate the doping concentration from carrier lifetime and quasi-Fermi level splitting. We find no changes in the effective lifetime, which is in the range of 200 ps. The doping concentration increases from 1016 cm−3 to 1017 cm−3. Our study shows that the increase in quasi-Fermi level splitting with higher deposition temperatures is not due to reduction in non-radiative recombination but due to increased doping concentration.