Approaching 19% Efficiency in (InxGa(1-x))2O3/CdSe/CdTe Solar Cells with Improved Front & Back Interfaces

Emitter layers play an important role in limiting front surface recombination in thin film solar cells. Recently, we presented experimental results for a new class of emitter layers based on (InxGa(1-x))2O3 (IGO). By varying x, the mole fraction of indium (In) in the alloy, we were able to tune the bandgap and conduction band offset (CBO) at the interface between the emitter and the CdSexTe(1-x) (CST) absorber layer. A 16.1% efficient device was fabricated when the (InxGa(1-x))2O3 bandgap was 4.02 eV, corresponding to a composition of x=0.36. Here we present results for the same (In0.36Ga0.64)2O3 emitter composition while the composition of the CdSexTe(1-x) (CST) layer was varied. Additionally, the back contact was formed using copper thiocyanide (CuSCN) as a source of copper (Cu) doping as well to introduce as a hole transport layer to minimize back surface recombination. A champion cell had an 18.8% efficiency with a Voc of 856 mV, a FF of 76.4 % FF, and a Jsc of 28.7 mAcm-2 when the device was fabricated with a CST layer that exhibited a bandgap of 1.41 eV after processing. The results demonstrate the potentiality for IGO as an emitter layer for high-efficiency CdTe-based solar cells.