Charge carrier dynamics and recombination in graded band gap CuIn1−xGaxSe2 polycrystalline thin-film photovoltaic solar cell absorbers

We report the results of spectroscopic time-resolved photoluminescence (TRPL) analysis for polycrystalline CuIn1−xGaxSe2 (CIGS) films. On the <5 ns time scale, we investigated minority carrier spatial redistribution from the initial absorption profile near the surface of the films to the conduction band minimum. Based on these data, the estimated minority carrier mobility is 75–230 cm2 V−1 s−1. Full TRPL decays were analyzed using models for donor-acceptor pair (DAP) recombination. We estimated that the concentration of DAP recombination centers was 5 × 1015–1017 cm−3. Data also show that Shockley-Reed-Hall and surface recombination are not significant for polycrystalline CIGS absorbers used in high-efficiency photovoltaic solar cells.