Reactive Ion Etched, Self-Aligned, Selective Area Poly-Si/SiO2 Passivated Contacts

Front/back poly-Si/SiO₂ contact devices suffer from low short-circuit current density, J_sc, due to parasitic optical absorption in the front poly-Si layer. Thin poly-Si (~20 nm) allows for high J_sc but is not compatible with screen-printed fire-through contacts. We therefore study the effects of post-deposition etching of a thick poly-Si (200 nm) front layer by reactive ion etching (RIE) using the metal grid lines as a self-aligned mask. We show that passivation is maintained in the device during RIE and that J_sc is increased by a gain in the blue quantum efficiency response. However, our specific etching parameters cause non-uniform etching of the poly-Si leading to premature loss of passivation without optimal gain in J_sc. Etched, unpassivated layers can be re-passivated with a H-containing dielectric layer leading to a gain in J_sc, open circuit voltage,V_oc, Fill-Factor, FF, and efficiency.