Thermally-stable and highly-efficient bi-layered NiOx-based inverted planar perovskite solar cells by employing a p-type organic semiconductor

• TPA-BA modification results in improved interfacial energy band alignment. • TPA-BA modification reduces interfacial chemical reactivity. • The TPA-BA-modified devices achieve a power conversion efficiency of 22.25%. • TPA-BA-based devices remained stable after illumination and thermal aging tests. Nickel oxide (NiO x ) is one of the most promising inorganic hole transport layers for perovskite solar cells (PSCs) due to its low cost, high hole mobility, and superior stability. However, the mismatched energy level and undesirable chemical reaction at the NiO x /perovskite interface limit the performance of NiO x -based PSCs. Herein, a p- type semiconductor TPA-BA is explored to modify the NiO x /perovskite interface and form an intermediate hole transport layer (HTL) between NiO x and perovskite for efficient and efficient stable PSCs. This molecule comprises triphenylamine and carboxyl function groups, which can be anchored on the NiOx surface and facilitate the hole transfer between the perovskite and NiO x layer by minimizing the interfacial band energy offset. Furthermore, the bi-layered NiO x HTL exhibited reduced chemical reactivity at NiO x /perovskite interface, which would otherwise lead to detrimental perovskite degradation. Thus, a champion PSC device with an open-circuit voltage value up to 1.15 V and a power conversion efficiency of 22.25% was demonstrated-a high value for NiO x -based PSCs. More importantly, the intermediated HTL modified PSCs exhibit significantly improved device stability compared with un-modified PSCs, retaining over 90 % of their initial efficiencies after 1000-h continuous operation under 1 sun illumination and thermal aging at 85 °C respectively. This work renders the promise of TPA-BA as the intermediated HTL in between p -type metal oxide and perovskite for optoelectronic applications.