Lattice Matching Anchoring of Hole-Selective Molecule on Halide Perovskite Surfaces for n-i-p Solar Cells

Exploiting the self-assembled molecules (SAMs) as hole-selective contacts has been an effective strategy to improve the efficiency and long-term stability of perovskite solar cells (PSCs). Currently, research works are focusing on constructing SAMs on metal oxide surfaces in p-i-n PSCs, but realizing a stable and dense SAM contact on halide perovskite surfaces in n-i-p PSCs is still challenging. In this work, the hole-selective molecule for n-i-p device is developed featuring a terephthalic methylammonium core structure that possesses double-site anchoring ability and a matching diameter (6.36 Å) with the lattice constant of formamidinium lead iodide (FAPbI₃) perovskite (6.33 Å), which facilitates an ordered and full-coverage SAM atop FAPbI₃ perovskite. Moreover, theoretical calculations and experimental results indicate that compared to the frequently used acid or ester anchoring groups, this ionic anchoring group with a dipolar charge distribution has much larger adsorption energy on both organic halide terminated and lead halide terminated surfaces, resulting in synergistic improvement of carrier extraction and defect passivation ability. Benefiting from these merits, the efficiency of PSCs is increased from 21.68% to 24.22%. The long-term operational stability under white LED illumination (100 mW cm^-2) and at a high temperature of 85 °C is also much improved.