Publication date: 16th July 2025
Mixed-halide perovskite materials are exceptional candidates for multijunction solar cells to surpass the detailed-balance limit. However, perovskite solar cells (PSC) still suffer performance losses due to nonradiative charge recombination, which is induced by electronic defects (traps). A common technique to assess nonradiative losses in semiconductors is photoluminescence (PL) spectroscopy. Using transient PL (tr-PL) measurements, we study the time-resolved recombination decay, providing insight into charge recombination kinetics. In metal-halide perovskites, these transients exhibit extremely long decay times dominated by trapping and de-trapping at shallow defects. [1]
Here, we investigate shallow defects in metal-halide perovskite partial solar cell stacks and examine how surface treatments modify their energy and density using low-temperature transient PL spectroscopy. At lower temperatures, PL decay is dominated by radiative recombination, with longer decay times suggesting reduced nonradiative losses. Fitting the temperature-dependent tr-PL indicates that, upon cooling, shallow traps appear less deep and eventually merge into the valence or conduction band. From these low-temperature transients, we extract activation energies and construct a shallow trap density of states (tDOS), visualizing defect distributions within the perovskite film. We extend this approach to films treated with choline chloride, fullerene C60, and choline chloride combined with C60, showing that these treatments alter the shallow tDOS and energy compared to untreated films, demonstrating that surface treatments influence shallow as well as deep defects.
Our results show that low-temperature tr-PL enables experimental probing of shallow defect densities and energies, providing a better understanding of shallow defects in metal-halide perovskite films and informing passivation strategies and charge transport layer design for higher-efficiency PSCs.
The authors acknowledge funding from the Dutch Research Council (NWO) (Spinoza grant) and the European Research Council (Grant Agreement No. 101098168).
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