Structure Engineering of Halide Double Perovskites
Feng Wang a, Fuxiang Ji a, Feng Gao a
a Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Oral, Feng Wang, presentation 151
Publication date: 20th April 2022

Lead-free halide double perovskites (HDPs, A2BIBIIIX6) with attractive optical and electronic features are regarded as one of the most promising alternatives to overcome the toxicity and stability issues of lead halide perovskites.[1] They provide a wide range of possible combinations and rich substitutional chemistry with interesting properties for various optoelectronic devices. We prepared high-quality double perovskite films based on double perovskites single crystals as precursors.[2]  The films are composed of high-crystal-quality grains with diameters equal to the film thickness, thus minimizing the grain boundary length and the carrier recombination. These perovskite films show long electron–hole diffusion lengths greater than 100 nm. Correspondingly, we demonstrated the first double perovskite (Cs2AgBiBr6) solar cells using the planar structure. To enhance the absorption properties of double perovskites, we adopted the metal doping strategy. By introducing Cu as the dopant in Cs2AgBiBr6, we significantly broaden the absorption edge from around 610 nm to around 860 nm.[3]  Systematic characterizations indicate that Cu doping introduces defect states (sub-bandgap states) in the bandgap, without changing the bandgap of Cs2AgBiBr6. Interestingly, these sub-bandgaps can generate considerable amount of band carriers upon optical excitation, making these double perovskites promising for near-infrared light detection. In addition, we also develop a crystallization control approach to narrow the bandgap of Cs2AgBiBr6, where high temperature is employed to assist the single crystal growth.[4] By simply increasing the crystal growth temperature from 60 oC to 150 oC, the bandgap of Cs2AgBiBr6 crystals can be reduced from 1.98 eV to 1.72 eV, which is the lowest reported bandgap for Cs2AgBiBr6 at ambient conditions. The underlying reason is hypothesized to be related to the increased level of Ag–Bi disorder in the crystal structure.

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