Diverse simulations of time-resolved photoluminescence in thin-film solar cells: A SnO2/CdSeyTe1−y case study

Abstract

Time-resolved photoluminescence (TRPL) is widely used to measure carrier lifetime in thin-film solar cell absorbers. However, the injection dependence of data and frequent non-exponential decay shapes complicate the interpretation. Here, we develop a numerical model to simulate injection-dependent TRPL measurements in a SnO2/CdSeyTe1−y solar cell structure, considering parameters of interest to researchers in industry and academia. Previous simulations have shown that in low injection, excess electrons and holes injected by the laser pulse are rapidly separated in the electric field formed by the pn junction. As a result, at early times, the PL signal can decay faster than the Shockley–Read–Hall lifetime in the absorber bulk (τbulk). Prior simulations have shown that the charge stored in the junction can slowly leak out to affect decays at late times. However, it has not been clear if and to what degree charge storage can affect the slopes extracted from TRPL decays—τ2—commonly cited as the TRPL-measured lifetime. Here, we show that charge storage can, in some cases, result in τ2 values that substantially overestimate τbulk. Previous simulations indicate that high-injection conditions can screen the junction field and minimize charge separation. Here, we show that continued injection increases can drive down τ2 below τbulk as radiative recombination becomes dominant. We catalog charge storage and radiative recombination impacts for a diverse set of material parameters and compare results to double-heterostructure models.