Selective Polysilicon Fingers

TOPCon solar cells (Tunnel Oxide Passivating Contact) have been developed by many research institutes and companies in recent years and are now increasingly being manufactured in industrial production and sold commercially. Cell voltages of just over 700 mV are achieved and efficiencies of 23.0% to 23.8% are attained. The voltage of such cells is mainly limited by recombination on the front side, which is why the next step is to improve the front side of the cell. Structured passivated contacts are necessary to avoid optical losses due to parasitic absorption.

The aim is to develop a process sequence for the cost-effective production of such structured passivated contacts. This is to be integrated into the standard process for TOPCon solar cells and is based on local laser doping of poly-silicon to produce p+ poly-silicon areas that are stable against etching in alkaline solutions. In this way, local passivated contacts are to be implemented on the front side of the solar cell in order to significantly increase the efficiency of the solar cell, primarily through an increased cell voltage of 715-720 mV. Another possible application of the process for producing such local contacts is in IBC solar cells (interdigitated back contact). Here, local treatment with the laser enables the production of separate p+ doped poly-silicon areas.

The Fraunhofer CSP's contribution aims to investigate and research the effect of contact resistance reduction through laser-enhanced contact optimization (LECO) technology. The application of LECO to solar cells with contacts passivated on both sides can reduce the contact resistance of the contacts and thus further increase the efficiency of the solar cell.