Electron beam induced current in photovoltaics with high recombination

TL;DR

This paper presents a model for electron beam induced current (EBIC) measurements in photovoltaics that accounts for high recombination within the depletion region, revealing spatial variations in carrier collection efficiency.

Contribution

A new EBIC measurement model is developed that explains reduced and spatially varying collection efficiency in high recombination photovoltaic devices.

Findings

Model reproduces experimental EBIC results with spatially varying mobility-lifetime product.

High-injection effects likely cause increased radiative recombination and reduced efficiency.

Experimental data on CdS-CdTe cells supports the model's predictions.

Abstract

Electron beam induced current (EBIC) is a powerful characterization technique which offers the high spatial resolution needed to study polycrystalline solar cells. Ideally, an EBIC measurement reflects the spatially resolved quantum efficiency of the device. In this work, a model for EBIC measurements is presented which applies when recombination within the depletion region is substantial. This model is motivated by cross-sectional EBIC experiments on CdS-CdTe photovoltaic cells which show that the maximum efficiency of carrier collection is less than 100 \% and varies throughout the depletion region. The model can reproduce experimental results only if the mobility-lifetime product $\mu\tau$ is spatially varying within the depletion region. The reduced collection efficiency is speculated to be related to high-injection effects, and the resulting increased radiative recombination.