Determination of transport properties in optoelectronic devices by time-resolved fluorescence imaging

In this article, we introduce time-resolved fluorescence imaging as an optical characterization method for optoelectronic devices. Under wide-field illumination, it allows obtaining time-resolved photoluminescence maps with a temporal resolution of 500 ps and a micrometric spatial resolution. An experiment on a GaAs-based solar cell is presented here as a proof of concept. Thanks to a model including diffusion and recombination of minority charge earners, we fit the experimental photoluminescence transients and extract key optoelectronic properties for the considered device. For various fluence levels, we determine an intrinsic bulk recombination lifetime tau(n) = 75 ns, a constant effective diffusion length L-eff = 190 mu m, which is characteristic for the lateral transport inside the solar cell, and an injection-dependent contact recombination velocity S-n, taking its values between 7 x 10(4) and 3 x 10(5) cm/s, which is explained by the saturation of defects. The wide-field illumination notably avoids lateral diffusion artefacts leading to a significant underestimation of tau(n) . Published by AIP Publishing.