Molecule-Cooperative Strategy for Dopant-Free Hole Transporting Layer toward Fully Printed High-Performance...

Enabling large-area deposition of dopant-free organic hole transport layers (HTLs) with high reproducibility and uniformity is crucial for fully printed n-i-p perovskite solar cell (pero-SC) modules. However, typical polymer hole transport materials (HTMs), with non-Newtonian fluid characteristics, show shear rate-dependent viscosity during the printing process, whereas blade-coated small-molecule HTLs often exhibit unfavorable assembly behavior and solute random distribution caused by molecular aggregation and low viscosity; these factors impose challenges on blade-coating of high-quality large-area HTL films. Here, we designed a dopant-free small molecule BDT-MB with high mobility and further proposed a molecular cooperative (MC) strategy by combining with polymer D18. The mechanism was clearly clarified that the pre-aggregated polymer D18 acted as a "seed crystal" to induce preferential face-on orientation of small molecule BDT-MB through intermolecular C─H···π interaction. This strategy not only suppresses the unfavorable assembly behavior of small molecular HTMs but also overcomes the solute random distribution by tuning the solution with high and constant viscosity. It facilitates printing large-area dopant-free HTLs with high uniformity and ordered fiber-like morphology. The resultant small-area pero-SCs (0.062 cm²) and large-area fully printed modules (15.64 cm²) both achieved record power conversion efficiencies (PCEs) of 24.46% (certified at 24.30%) and 21.04%.