Cost-saving and performance-enhancement of CuInGaSe solar cells by adding CuZnSnSe as a second absorber

Abstract

CuInGaSe (CIGS) based solar cells are promising, but involve costly and hazardous and costly indium element. This work aims at solving these problems, without sacrificing the benefits of CIGS systems. The approach is to use thinner CIGS layers. However, very thin layers minimize absorption and lower cell performance. Adding a second CuZnSnSe (CZTSe)-layer absorber should maintain high cell performance. The new proposed cell that has been simulated is MgF2/ZnO/Al/ZnO:i/CdS(n)/CZTSe(p)/CIGS(p)/Mo, with MgF2 antireflection layer, ZnO:i passivating layer, CdS emitter layer, CZTSe/CIGS double absorber layer, ZnO-Al transparent conductor oxide(TCO) and element almolybdenum (Mo) back contact. A ZnO-Al film has been experimentally electrodeposited onto FTO/Glass substrate, and then characterized. TCAD SILVACO using ATLAS module has been used in the simulation. Various parameters, including layer-thickness and doping-concentration, are optimized, keeping smaller CIGS-layer thickness. Band-diagrams, carrier-concentrations and current–density, in addition to possible recombination processes, are investigated to assess performance enhancement. The results show that increasing the one-absorber CIGS-layer thickness by 2.5-fold, increases conversion efficiency from 22.3 to 24.3% only, which does not justify the extra costs. Alternatively, efficiency improves from 22.40 to 29.22% by adding CZTSe to a thin 1.0 μm CIGS layer. In conclusion, the study highlights the added value for the second-absorber layer.