Efficient electron transfer layer based on Al2O3 passivated TiO2 nanorod arrays for high performance evaporation-route deposited FAPbI3 perovskite solar cells

•Al2O3 passivated TiO2 NRs as electron transfer layer for evaporation FAPbI3 PSCs.•Al2O3 layer induces fluorescence quenching and reduces charge recombination.•Al2O3 retard electrons reverse transport and enhance electron extraction in ETL.•Evaporation route obtains homogeneous FAPbI3 film and compact interface.•PSCs display a strikingly PCE of 14% with negligible hysteresis.

Interfacial engineering related to charge transfer plays a vital role in boosting performance of perovskite solar cells (PSCs). For the first time, we report Al2O3 layer passivated TiO2 nanorods (NRs) array as an electron transfer layer (ETL) for thermal evaporation-route synthesized formamidine lead iodine (FAPbI3) PSCs. The modification of Al2O3 layer on TiO2 NRs can efficiently enhance charge transport and retard charge recombination at interface between ETL and FAPbI3 layers. PSCs based on evaporation-fabricated FAPbI3 absorption layer and Al2O3-TiO2 ETL display excellent photoelectronic performance, showing a high photoelectric conversion efficiency of 14% with negligible hysteresis and excellent reproducibility and stability. Al2O3 passivation can induce an obvious fluorescence quenching phenomenon and reduced electron-hole recombination rate. The greatly improved performances can be attributed to the following three factors. Firstly, Al2O3 buffer layer as a barrier can effectively retard electrons in ETL reversely transport and impede charge carrier recombination. Secondly, Al2O3 passivation can enhance the TiO2/FAPbI3 interface contacts, alleviate the electron trapping effect resulted from the surface defects at TiO2/perovskite interface, benefiting for electron extraction to be transported directly toward FTO. Thirdly, the evaporation synthetic route is helpful to get extremely homogeneous FAPbI3 film without any pinholes and compact interface.

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