Controlling Diffusion in Poly-Si Tunneling Junctions for Monolithic Perovskite/Silicon Tandem Solar Cells

Christoph Luderer,Frank Feldmann,Michaela Penn,Christian Reichel,Susanne Richter,Angelika Hahnel,Volker Naumann,Jan Christoph Goldschmidt,Martin Hermle,Martin Bivour

doi:10.1109/jphotov.2021.3101177

Abstract

The performance of a low-resistive p + /n + poly-Si tunneling junction (SiTJ) based on a tunnel oxide passivating contact in dependence on the thermal budget of the applied post-deposition treatment is studied. We present two approaches to reduce the performance limiting parasitic dopant interdiffusion and, thus, the contact resistivity, without impairing the passivation quality. Both, carbon-alloying of poly-Si layers and the application of diffusion blocking interlayers are effective means to maintain a low contact resistivity of ∼24 mΩcm 2 at high thermal process temperatures of up to 950 °C. Those low values are obtained using either a standard furnace anneal or a rapid thermal process (RTP). We report on promising results toward a lean process sequence using only one single fast thermal treatment (RTP-only). As a main result, the flexibility for engineering and fabrication of our SiTJ was markedly improved, eventually facilitating industrially feasible perovskite/silicon tandem solar cells. One aspect being higher post-deposition temperatures needed for, e.g., bottom cell rear side contact formation and the first layers of the perovskite to cell.

Highlights

W ITH the recent world record efficiency of 29.5% for a perovskite/silicon tandem [1] exceeding the theoretical efficiency limit of 29.4% for a silicon (Si) single junction [2], tandem solar cells are getting more and more attention from the photovoltaic community
Without any postdeposition thermal treatment, a high and homogenous phosphorous (P) concentration was observed within a-Si:H(n+) which abruptly decreased to a very low level within a-Si:H(p+) and c-Si
A p+/n+ poly-Si tunneling junction (SiTJ) based on tunnel oxide passivated front contact (TOPCon) was presented

Summary

INTRODUCTION

W ITH the recent world record efficiency of 29.5% for a perovskite/silicon tandem [1] exceeding the theoretical efficiency limit of 29.4% for a silicon (Si) single junction [2], tandem solar cells are getting more and more attention from the photovoltaic community. Such a configuration requires low-ohmic and transparent interconnection of both subcells. An alternative are Si-based tunneling junctions (SiTJs), as first demonstrated in a perovskite/Si tandem cell by Mailoa et al [9], which have the benefit of better refractive index matching between the subcells and reducing reflection losses [10]. They have the potential to be directly integrated in the processing of the bottom cell’s passivating contact [11]–[15].

EXPERIMENTAL

RESULTS

Carbon-Alloyed SiTJ

Diffusion Blocking Interlayer

In-Depth Analysis of SiCx and SiNx Interlayers

CONCLUSION