Carrier Lifetime as a Developmental and Diagnostic Tool in Silicon Heterojunction Solar Cells

Minority carrier lifetime measurements were used to optimize processes for amorphous/crystalline silicon heterojunction solar cells. A blue filter highlights surface lifetime and is used to determine the interaction between the front and rear depositions. On n-type substrates, depositing the front p-type layer first led to contamination of the rear surface such that a subsequent n-type deposition on the rear intended as a back surface field had no passivating quality and giving cells with low open-circuit voltages only 580 mV. Switching the order of deposition and depositing the rear n-layer first, improved the quality of the rear passivation and subsequently increased open circuit voltages to over 620 mV; without intrinsic buffer layers. Depositions of intrinsic material resulted in lifetimes of 2.4 ms, and wafer cleaning was found to have a significant impact on measured lifetime. Finally, immersion in hydrofluoric acid was found to be the easiest way to measure substrate lifetime above 1 ms