Experimental verification of internal resistance models for PERT-type solar cells

Abstract

We present different models for the internal resistance of passivated emitter and rear totally diffused (PERT) solar cells. First we apply the model of Gelmont and Shur for the spreading resistance of a passivated emitter and rear cell (PERC) structure with line-shaped contacts and adapt this model to account for the elliptic contact shape of Al-alloyed contacts. To account for the additional vertical current flow through the silicon wafer and the lateral current flow through the back surface field (BSF) of a PERT structure, we evaluate an alternative model using the analogy to the transfer length method (TLM) problem. For experimental verification, we have fabricated resistance test structures for various wafer resistivities, BSF doping levels and line distances (finger pitches) of the line-shaped contacts. Our experimental data shows good agreement with the presented models in distinct parameter ranges and thus offers a solid basis for analytical modelling of PERT-type solar cells.