Interfacial engineering has been considered one of the most effective methods for further enhancing the performance of perovskite solar cells. Herein a facile but effective interfacial engineering method of modifying NiO x coated substrate by PTAA is demonstrated for inverted planar perovskite solar cells. The surface modification by polymeric PTAA could effectively tailor the quality of perovskite absorber layer with larger grain size and better crystallinity by controlling wettability of NiO x surface with varied thickness of hydrophobic PTAA. The improvement of J sc was ascribed to the improved perovskite film quality with reduced trap state densities. By EIS and TRPL analysis, it was also confirmed that PTAA modification significantly facilitated interfacial charge transfer at the interface between perovskite and PTAA/NiO x due to the gradient band alignment. As a consequence, the highest power conversion efficiency of 17.1% together with negligible hysteresis effect was achieved from planar perovskite solar cells with 0.5 mg/mL optimal concentration of PTAA.

The elaborate control of the surface morphologies and trap states of solution-processed perovskite films significantly governs the photovoltaic performance and moisture resistance of perovskite solar cells (PSCs). Herein, a thin layer of poly­(triaryl amine) (PTAA) was unprecedentedly devised on top of perovskite quasi-film by spin-coating PTAA/chlorobenzene solution before annealing the perovskite film. This treatment induced a smooth and compact perovskite layer with passivated surface defects and grain boundaries, which result in a significantly reduced charge recombination. Besides, the time-resolved photoluminescence spectra of the PTAA-treated perovskite films confirmed a faster charge transfer and a much longer lifetime compared to the control cells without the PTAA treatment. Moreover, such a hydrophobic polymer atop the perovskite layer could effectively protect the perovskite against humidity and retain 83% of its initial efficiency in contrast to 56% of control cells stored for 1 month in ambient conditions (25 °C, 35 RH%). As a result, the PTAA-treated PSCs displayed an average efficiency of 17.77% (with a peak efficiency of 18.75%), in contrast to 16.15% of the control cells, and enhanced stability. These results demonstrate that PTAA and the method thereof constitute a promising passivation strategy for constructing stable and efficient PSCs.