Study of Passivation in the Gap Region Between Contacts of Interdigitated-Back-Contact Silicon Heterojunction Solar Cells: Simulation and Voltage-Modulated Laser-Beam-Induced-Current

Maximizing the lateral transport and collection of photogenerated carriers near the rear surface of the interdigitated-back-contact silicon heterojunction solar cell (IBC-SHJ) is critical for high efficiency. Specifically, this requires minimizing the recombination over the gap region between the well-passivated emitter and base contacts. In this paper, we investigate the potential of a p-type amorphous silicon and intrinsic hydrogenated amorphous silicon layer stack, which forms an inversion layer for n-type crystalline Si (n.c-Si) surfaces, to provide gap passivation for a scalable low-temperature IBC-SHJ fabrication process. We fabricate novel three terminal rear heterojunction silicon devices to understand the effect of this gap passivation structure in terms of carrier distribution and transport mechanisms when localized high recombination regions are introduced due to the simplified fabrication process. Voltage-modulated laser-beam-induced-current measurements are utilized to characterize the device performance before and after introducing intentional localized laser damage. Interpretation of results is aided by one-dimensional simulation of band alignments and charge distribution at different voltage-modulations under illumination. We confirmed that the gap passivation structure that induces an inversion layer at the surface should be avoided to eliminate any parasitic shunting or inversion-layer-assisted-recombination on n.c-Si IBC-SHJ, and this is applicable to any n-type IBC cells in general.