Regular Article

Stable reverse bias or integrated bypass diode in HIP‑MWT+ solar cells

¹ Fraunhofer Institute for Solar Energy Systems ISE, 79110 Freiburg, Germany
² Department for Sustainable Systems Engineering, University Freiburg, 79098 Freiburg, Germany

^* e-mail: tadeo.schweigstill@ise.fraunhofer.de

Received: 30 June 2021
Received in final form: 22 November 2021
Accepted: 24 December 2021
Published online: 31 January 2022

Abstract

The Metal Wrap Through+ (HIP-MWT+) solar cell is based on the PERC concept but features two additional electrical contacts, namely the Schottky contact between p-type Si bulk and Ag n-contact and the metal-insulator-semiconductor (MIS) contact on the rear side of the cell below the n-contact pads. To prevent thermal hotspots under reverse bias, both contacts shall either restrict current flow or allow a homogenous current flow at low voltage. In this work we present both options. First the stable reverse bias characteristics up to −15 V with a MIS contact using industrially manufactured SiON passivation and second, an integrated by-pass diode using AlO_X as insulator in the passivation stack allowing current flows at approximately V_rev = –3.5 V depending on the chosen screen-print paste. The examined Schottky contacts break down at around V_rev = –2.5 V. Reverse bias testing of the cells reveals a solid performance of the cells under reverse bias and an average conversion efficiency of η = 21.2% (AlO_X) and η = 20.7% (SiON), respectively.