Accumulation Versus Inversion Layer Passivation on +19% Screenprinted Industrial Crystalline Silicon Solar Cells

This paper describes the progress in transferring a PERC type cell structure based on Al2O3/SiNx or SiO2/Al2O3/SiNx passivation into an industrial environment. Al2O3-layers deposited in an industrial type spatial ALD system are characterized using C-V, ellipsometry and lifetime measurements. A negative charge density above 10 cm was measured for a 6 nm thick layer. The Al2O3-layers are successfully incorporated in a PERC process sequence for monocrystalline Cz-Si solar cells. This process is based on a production type homogeneous POCl3diffused emitter, rear surface polishing and screenprinted contacts. Average efficiencies above 19% have been obtained with a thin dielectric stack of Al2O3 and SiNx relying on accumulation layer passivation on the rear surface. A thin thermally grown oxide further improves the Voc due to a lower emitter dark saturation current density. On the rear surface this thin oxide, with Al2O3 and SiNx on top, results in inversion layer passivation. Care is taken to avoid inversion layer shunting by improving the Back Surface Field around the local contacts using the Extended Laser Ablation (ELA) process. This resulted in an average efficiency of 19.46% for a batch of 140 Cz-Si cells with a top efficiency of 19.7%.