Constructing hole transport channels in the photoactive layer connecting dopant-free hole transport layers to improve the power conversion efficiency of perovskite solar cells

Perovskite solar cells (PSCs) with dopant-free hole transporting layers (HTLs) deserved extensive research by merits of their outstanding hydrophobicity and stability. However, the low carrier mobility and poor interfacial hole extraction lead to the inferior power conversion efficiency (PCE) than that of conventional Li+ doped Spiro-OMeTAD. Here, a design of triphenylamine groups grafted triphenylene derivative (T-6TPA) as dopant-free HTLs has been presented. The larger pi-conjugation in T-6TPA give rise to high hole mobility of 2.06 x 10-3 cm2V- 1s- 1. Moreover, the interfacial hole extraction of T-6TPA was significantly promoted when the molecules were infiltrated into perovskite before HTL deposition. The infiltration method of anti-solvent dripping (An) strategy increased PCE from 18.5% up to 20.3%, which is superior to another additive doping strategy (Ad -strategy, 19.3%). The effectiveness of An-strategy can be attributed to the construction of a coherent and ho-mogeneous hole transport channel. The hydrophobicity and high glass transition temperature of T-6TPA also granted excellent moisture and thermal stabilities that the initial PCE could remain 80% for 60 days in air or 600 h at 60 degrees C. This work highlights the synergistical optimization by design of highly hole-mobile materials as well as the interfacial network construction for charge transport.