Breaking 26% efficiency for n-i-p perovskite solar cells via synergistic geometry modulation of hole semiconductors.

Enhancing the molecular planarity and the π-conjugation degree of hole transport materials represents an effective strategy to improve the hole mobility and achieve high-efficiency perovskite solar cells (PSCs). However, such structural optimization often results in excessive molecular aggregation, which makes it challenging to control the uniformity and microstructure of the film, thereby affecting the controllable fabrication and performance stability of the device. To tackle the long-standing "trade-off" dilemma in this field, we herein report a synergistic geometry modulation strategy, which can be easily implemented by incorporating side chains and π-bridges near the junction between the central core and peripheral arms. Noteworthy, the surrounding steric hindrance can reciprocally verticalize side-chain orientation and increase the torsion angle of periphery to modulate intermolecular stacking geometry. Meanwhile, the versatile vinylene π-bridge can concurrently improve molecular coplanarity and rigidify intramolecular skeleton geometry. Consequently, the synergistically modulated WH07 achieves optimal balance between hole mobility and film morphology. As a result, up to 26.31% PCE with impressive durability (ISOS T90 lifetime > 500 h) is yielded for the WH07-based device, which ranks amongst the best results for n-i-p PSCs. These findings demonstrate that the synergistic intra- and inter-molecular geometry modulation is a promising approach for the comprehensive optimization of molecular semiconductors in high-performance perovskite photovoltaics.