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Hybrid metal halide perovskites are attractive components for many optoelectronic applications due to a combination of their superior charge transport properties and relative ease of fabrication.
A complete understanding of the nature of charge transport in these materials is therefore essential for current and future device development. We have evaluated two systems – the standard perovskite methylammonium lead triiodide (CH3NH3PbI3) and a series of mixed-iodide/bromide formamidinium lead perovskites – in an effort to determine what effect structural and chemical composition have on optoelectronic properties including mobility, charge-carrier recombination dynamics, and charge-carrier diffusion length.
The photoconductivity in thin films of CH3NH3PbI3was investigated from 8 K to 370 K across three structural phases [1]. While the monomolecular charge-carrier recombination rate was found to increase with rising temperature indicating a mechanism dominated by ionized impurity mediated recombination, the bimolecular rate constant decreased with rising temperature as charge-carrier mobility declined. The Auger rate constant was highly phase specific, suggesting a strong dependence on electronic band structure.
For the mixed-halide formamidinuim lead bromide-iodide perovskites, HC(NH2)2Pb(BryI1–y)3, bimolecular and Auger charge-carrier recombination rate constants strongly correlated with bromide content, which indicated a link with electronic structure [2]. Although HC(NH2)2PbBr3 and HC(NH2)2PbI3 exhibited high charge-carrier mobilities and diffusion lengths exceeding 1 μm, mobilities for mixed Br/I perovskites were all lower as a result of crystalline phase disorder.
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