Simplified processing of interdigitated-back-contacted silicon heterojunction solar cells

Abstract

Silicon heterojunction (SHJ) solar cells are one of the most promising PV technologies nowadays due to high photoconversion efficiencies and low manufacturing costs. However, standard front/back-contacted (FBC) solar cells feature a front metal grid that brings shading to the front side of the devices, which limits the conversion efficiency of solar cells. One solution is to move metal contacts fully to the back by introducing interdigitated-back-contacted (IBC) architecture. In 2018, IBC-SHJ solar cells achieved a photoconversion efficiency of 26.7% holding a record for single-junction c-Si cells. However, the standard fabrication process of IBC solar cells comes with increased complexity and manufacturing costs. The focus of this research is on developing and optimizing a simple and industry-appealing fabrication process for high-efficiency IBC-SHJ solar cells.

The first part of the project investigates the simple processing of IBC-SHJ solar cells featuring tunneling recombination junction (TRJ). The first tunneling IBC devices are fabricated successfully. However, shunting is observed from the J-V curves of fabricated devices, which can be related to the internal shunting of tunneling IBC architecture and high lateral conductivity of p-type nc-Si:H-based blanket layer. Hence, alternative contact stacks are designed for application in the previously developed flowchart with the aim to minimize the lateral conductivity of the blanket layer and keep the fabrication process simple.

The proposed hole collection contact stack is firstly implemented in the front junction (FJ) FBC solar cells. The FJ FBC devices reach Voc of 704 mV and FF of 79.29% . Rear junction (RJ) FBC solar cells are fabricated featuring a novel electron collection contact stack that is developed within this thesis. Voc of 715 mV and FF of 82.24% are obtained in RJ devices. The results of RJ FBC solar cells with a newly developed contact stack show excellent results in terms of FF, making it a promising candidate for further application in IBC devices. The introduction of the optimized device design enabled the successful fabrication of IBC solar cells with the simple process developed for tunneling IBC devices while ensuring no shunting occurs. Fabricated devices represent a proof-of-concept of the novel configuration, providing a promising starting point for future development.