The use of HfO2 in a point contact concept for front interface passivation of Cu(In,Ga)Se-2 solar cells

Abstract

We report on the use of a high bandgap metal-oxide at the front interface of Cu(In,Ga)Se-2 (CIGS) solar cells in a point contact concept for reduced interface recombination. Highly resistive HfO2 is applied on the CIGS surface by atomic layer deposition (ALD). Aspects of the surface passivating effect of HfO2 on CIGS were investigated by time-resolved photoluminescence (TRPL), electron beam induced current (EBIC) and capacitance-voltage (C-V) measurements. Two structuring methods for point contact formation are compared, a lithographic top-down and a simple bottom-up approach using NaCl as template. The former method employed a plasma etch step which was found to degrade the performance of solar cells when applied on the CIGS surface. The template method omitted sputtering and allowed patterning of HfO2 up to 10 nm thickness without adversely impacting the open-circuit voltage (V-OC). EBIC revealed an improved carrier collection due to the HfO2 coating and a long term stable PL decay was observed. Yet, the point contact concept with HfO2 was not significantly influencing the performance of a CIGS solar cell for the investigated parameter range.