Structural and Electronic Defects in Layered Hybrid Perovskites

Solution-processable, hybrid halide Ruddlesden-Popper phases have favorable electronic properties with increased stability relative to their 3D counterparts (CH₃NH₃PbI₃). Although layer confinement leads to anisotropic charge transport, our previous work shows that the in-plane mobility of single-layer Pb-I perovskite sheets is comparable to CH₃NH₃PbI₃,¹ making control over thin-film structure essential to device performance. Here we study R-P compounds with an n-butylammonium cation, (BA)₂(MA)_n-1Pb_nI_3n+1, with varying thickness of Pb-I perovskite sheets. Specular diffraction shows a gradual change in thin-film texture with increasing n, with the Pb-I sheets changing from parallel to perpendicular with respect to the substrate, however; disorder is apparent from grazing-incidence diffraction. Time-resolved microwave conductivity measurements show carrier lifetimes smaller than in MAPbI₃. Most interestingly, external quantum efficiency measurements of solar cells formed with these materials show sharp absorption edges despite structural disorder. From this, we conclude that these R-P phases have a high electronic defect tolerance and their performance is related to the alignment of the layers relative to the direction of transport.

¹J. G. Labram et al, J. Mater. Chem. C (2017).