Charge‐Carrier Trapping and Radiative Recombination in Metal Halide Perovskite Semiconductors

• Published in: Advanced functional materials 2020-10, Vol.30 (42), p.n/a
• Main Authors: Trimpl, Michael J., Wright, Adam D., Schutt, Kelly, Buizza, Leonardo R. V., Wang, Zhiping, Johnston, Michael B., Snaith, Henry J., Müller‐Buschbaum, Peter, Herz, Laura M.
• Format: Article
• Language: English
• Subjects: Carrier recombination; Cesium; Channels; charge‐carrier accumulation; Current carriers; Decay rate; Density; Materials science; Metal halides; Optoelectronic devices; perovskite; Perovskites; Phase transitions; Photoluminescence; Photovoltaic cells; Radiative recombination; Solar cells; trap states; Trapping
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202004312

Trap‐related charge‐carrier recombination fundamentally limits the performance of perovskite solar cells and other optoelectronic devices. While improved fabrication and passivation techniques have reduced trap densities, the properties of trap states and their impact on the charge‐carrier dynamics in metal‐halide perovskites are still under debate. Here, a unified model is presented of the radiative and nonradiative recombination channels in a mixed formamidinium‐cesium lead iodide perovskite, including charge‐carrier trapping, de‐trapping and accumulation, as well as higher‐order recombination mechanisms. A fast initial photoluminescence (PL) decay component observed after pulsed photogeneration is demonstrated to result from rapid localization of free charge carriers in unoccupied trap states, which may be followed by de‐trapping, or nonradiative recombination with free carriers of opposite charge. Such initial decay components are shown to be highly sensitive to remnant charge carriers that accumulate in traps under pulsed‐laser excitation, with partial trap occupation masking the trap density actually present in the material. Finally, such modelling reveals a change in trap density at the phase transition, and disentangles the radiative and nonradiative charge recombination channels present in FA0.95Cs0.05PbI3, accurately predicting the experimentally recorded PL efficiencies between 50 and 295 K, and demonstrating that bimolecular recombination is a fully radiative process. The properties of trap states that limit the performance of hybrid perovskite solar cells and light‐emitting devices are still under much debate. Herein, a unified model is presented, that accurately describes trap‐related and higher‐order charge‐carrier recombination. This work reveals the importance of explicit accounting for charge‐carrier trapping, detrapping and accumulation, and disentangles radiative and nonradiative recombination channels.