Process development of TOPCon rear junction n-type solar cells

Abstract

Global warming is currently being regarded as one of the most significant concerns in society. As globalnwarming is related to the greenhouse gases emitted from the current energy supply, there is a needbfor renewable energy sources. Solar energy is an energy source which has zero emissions and could
in theory supply the energy demand. A solar cell is technology based on the photovoltaic effect, it converts solar irradiance, specifically the energy derived from photons, into electrical energy. Over the course of the development of photovoltaic technology, numerous variations of solar cells have been introduced. By IRTPV, it is anticipated that new and advanced concepts, especially the Tunnel Oxide Passivating Contact (TOPCon) solar cell, will come to dominate the solar market in the coming years. At ISCKonstanz, the primary objective is to develop solar cells that are feasible for industrial applications.
The solar cell under investigation and exploration within the context of this particular thesis is referred to as TOPCon Rear Junction (TOPCon RJ), it differs from the well-documented TOPCon emitter Front Junction (FJ). The notable advantage lies in the fact that by placing the emitter at the RJ, the FSF can be
lightly doped, thereby reducing Auger recombination. Another advantage is the possibility of increasing the metal pitch between the fingers, reducing the metal used. Even more, the TOPCon RJ doesn’t need the high temperature boron diffusion needed for TOPCon FJ, because of doping during APCVD deposition. Simulation results indicate that TOPCon RJ can achieve at least the same
efficiency as TOPCon FJ. The TOPCon solar cell is developed on large area n-type Cz wafers, with a selective n++/n+ FSF of c-Si, a by APCVD inline deposited p+ poly-Si layer and screen printed silver contacts. The inline APCVD has fast processing as a major advantage. A comprehensive description of the TOPCon RJ solar cell structure will be provided. The solar cell’s parameters will be elaborated on, in order to characterize it. The report incorporates basic supportive solar physics. Various characterization methods will be expounded upon to offer a more comprehensive understanding of the research methodology. The research is divided into three parts: the development of the p+ poly-Si rear layer, the development of the n+ c-Si FSF, and the process of metallization. Good passivation for the individual layers were achieved and good contacting as well. However, viable cell results were not yet obtained. The research necessitates substantial further enhancements. Moreover, the presence of defects and damages significantly impacted the outcomes, lowering the reliability.