Numerical Simulations of Time-Resolved Photoluminescence in CdSexTe1-x/CdTe Solar Cells

We present initial time-resolved photoluminescence (TRPL) simulations in graded CdSexTe1-e thin-film solar cells to quantify the front-interface recombination velocity, Sint,front. Our model includes several composition dependences: bandgap energy, absorption coefficient, electron affinity, and carrier lifetime. Cathodoluminescence spectrum imaging measurements on bevels provide an estimate of the bandgap and the CdSexTe1-x alloy composition through the absorber thickness. TRPL decays are simulated as a function of the laser power, Sint,front, front-interface band offset, and bulk Shockley-Read-Hall lifetime. We find the impact of Sintf,ront on the PL decay increases as the band offset shifts from a “spike” to a “cliff”. Recombination rate analysis shows that back-interface recombination could potentially dictate the later part of the TRPL decay “τ2” in high-lifetime CdSexTe1-x cells. We briefly discuss ongoing work to determine TRPL measurement conditions that maximize sensitivity to Sitnt,front.