Development of rear surface passivated Cu(In,Ga)Se2 thin film solar cells with nano-sized local rear point contacts

Abstract

For the first time, a novel rear contacting structure for copper indium gallium (di)selenide (CIGS) thin film solar cells is discussed theoretically, developed in an industrially viable way, and demonstrated in tangible devices. The proposed cell design reduces back contacting area by combining a rear surface passivation layer and nano-sized local point contacts. Atomic layer deposition (ALD) of Al2O3 is used to passivate the CIGS surface and the formation of nano-sphere shaped precipitates in chemical bath deposition (CBD) of CdS to generate point contact openings. The Al2O3 rear surface passivated CIGS solar cells with nano-sized local rear point contacts show a significant improvement in open circuit voltage (VOC) compared to unpassivated reference cells. Comparing the passivated devices to solar cell capacitance simulator (SCAPS) modeling indicates that this increase is attributed to a decrease in rear surface recombination of a few orders.