Flexible perovskite solar cells (f-PSCs) show great promise in portable-power applications (e.g., chargers, drones) and low-cost, scalable productions (e.g., roll-to-roll). However, in conventional n-i-p architecture f-PSCs, the lowtemperature processed metal oxide electron transport layers (ETLs) usually suffer from high resistance and severe defects that limit the power conversion efficiency (PCE) improvement of f-PSCs. Besides the enhancement in the mobility of metal oxide and passivation for perovskite/ETL interfacial defects reported in previous literature, herein, the electron transport loss between the metal oxide nanocrystallines within the ETL is studied by introducing an amorphous F-doped TiO x (F-TiO x ) caulked crystalline SnO 2 composite ETL. The F-TiO x in this novel composite ETL acts as an interstitial medium between adjacent SnO 2 nanocrystallines, which can provide more electron transport channels, effectively passivate oxygen vacancies, and optimize the energy level arrangement, thus significantly enhancing the electron mobility of ETL and reducing the charge transport losses. The composite ETL-based f-PSCs achieve a high PCE of 22.70% and good operational stability. Furthermore, a moderate roughness of the composite ETL endows f-PSCs with superior mechanical reliability by virtue of a strong coupling at the ETL/perovskite interface, by which the f-PSCs can maintain 82.11% of their initial PCE after 4000 bending cycles.

The CuI hole transporter-based perovskite solar cells are prepared via a low-temperature in situ deposition method. As demonstrated, the results of XRD indicate that the CuI hole-transporter has been fabricated successfully and obtained a better stability, and can be supported by the corresponding scanning electron microscopy (SEM), including the dense surface and clear cross section. Further, a maximum incident photon-to-electron conversion efficiency (IPCE) of ~16.78% obtained at the CuI-based perovskite solar cell with 2nd time deposition, which is mainly attributed to that, with the fewer defect of high-quality interface and matched potential structure for promoting carrier interface immigration/diffusion, the CuI-based hole-transporter exhibits decent hole-extraction to make photo-generated electron/hole being a matched mobility, and the remained PbI2 with a better passivation can inhibit the carrier recombination, both can improve the IPCE efficiently. Therefore, such lower cost and easy controlled technique is suitable for large-scale solar cells.