Meanwhile, parameters including the FTO/perovskite interface defect density as well as the doping concentration of the front contact (FTO) were identified to significantly influence the performance of the device. In particular, the interface quality at the FTO/perovskite interface has greater impact on the device parameters than that at the perovskite/HTL interface, which suggests that more attention should be paid to the front FTO/perovskite interface to further enhance the performance of electron transport layer-free device. Appropriate interface defect passivation to reduce the interface defect density to the order of ~1015 cm−3 is necessary and urgently needed. Lastly, the effect of the electron and hole mobility and carrier diffusion length of CH3NH3PbI3−xClx were also analyzed and the results revealed that the mobility and diffusion length experimentally reported (~1.0 µm) are large and long enough for high efficiency.
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