21%-efficient silicon solar cells using amorphous silicon rear side passivation

Stacks of amorphous silicon and silicon oxide â all deposited by PECVD - are used to passivate the rear surfaces of high-efficiency solar cell structures on p-type float zone substrates. Energy conversion efficiencies of up to 21.7 % can be reported. An investigation of the effect of a post-process annealing at different temperatures is presented with I-V and IQE measurements leading to the conclusion that the rear surface passivation is stable until a temperature of 400 °C. Additionally, investigations on the passivation quality of single layer amorphous silicon and stacks of amorphous silicon and silicon oxide were performed. Surface recombination velocities below 6 cm/s could be measured leading to an excellent surface passivation of p-type float zone wafers (1 ohm cm).