Phytic acid dipotassium as a hole transport layer for stable tin halide perovskite solar cells with tailored interfacial chemical interaction

Tin halide perovskite (THP) is considered a prominent candidate for lead-free perovskite photovoltaic applications. However, the operational stability and durability of THP devices are severely limited by the weak interactions between the hole transport layer (HTL) and THP. Herein, a novel hole transport material phytic acid dipotassium (PADP) with tailored interfacial chemical interaction has been developed. The abundant -PO(OH)₂ groups in the PADP molecule can strongly interact with perovskite, which is crucial for modulating the perovskite crystallization process to achieve rapid nucleation and slow growth. As confirmed by the in-situ spectral characterization technique, the tailored interaction between PADP and perovskite could reduce the Gibbs free energy for heterogeneous nucleation and increase the activation energy of perovskite crystallization, leading to high-quality THP films on the PADP HTL. Moreover, the most significant result of the tailored interaction between PADP and perovskite was the void-free interface and the formation of two-dimensional perovskite at the buried interface between PADP and perovskites, which suppressed the ion migration with improved device stability. Consequently, the tin perovskite solar cell based on PADP with an efficiency of 12.45% achieved remarkable stability, retaining 90% of initial efficiency after continuous light illumination for 2000 h at the maximum power point.