Regular Article

Rear side dielectrics on interdigitating p⁺-(i)-n⁺ back-contact solar cells − hydrogenation vs. charge effects

¹ Institute for Solar Energy Research Hamelin (ISFH), Am Ohrberg 1, 31860 Emmerthal, Germany
² Institute of Electronic Materials and Devices, Leibniz Universität Hannover, Schneiderberg 32, 30167, Germany
³ Laboratory of Nano and Quantum Engineering, Leibniz Universität Hannover, Schneiderberg 39, 30167, Germany
⁴ Institute for Solid State Physics, Leibniz Universität Hannover, Appelstraße 2, 30167, Germany

^* e-mail: rienaecker@isfh.de

Received: 1 July 2021
Received in final form: 21 September 2021
Accepted: 22 October 2021
Published online: 9 November 2021

Abstract

Polysilicon-on-oxide (POLO) passivating contacts and interdigitated back-contact (IBC) cell technologies have recently attracted a lot of interest as candidates for the implementation in the next generation of solar cells. An IBC cell with POLO junctions for both polarities − a POLO²-IBC cell − has to electrically isolate the highly defective p⁺ and n⁺ poly-Si regions on the rear side of the cell to avoid parasitic recombination. Inserting an initially undoped, intrinsic (i) region between the p⁺ and n⁺ poly-Si regions was demonstrated to successfully prevent the parasitic recombination in the transition region of ISFH's 26.1%-efficient POLO²-IBC cell. In order to further improve the conversion efficiency towards 27%, we apply hydrogen-donating dielectric layer stacks to the p⁺-(i)-n⁺ POLO interdigitating rear side to enhance the passivation quality of the POLO junctions. We indeed show a significant improvement of POLO junctions on symmetrical full-area homogenously doped reference samples, but when we apply a hydrogen-donating layer stack on the p⁺-(i)-n⁺ POLO interdigitating rear side, we observe a strong degradation in the performance of the POLO²-IBC cell. We attribute this to the formation of a conductive channel between the p⁺ and n⁺ poly-Si regions due to the strong negative charge density of the hydrogen-donating layer stack.