Crosslinked and dopant free hole transport materials for efficient and stable planar perovskite solar cells

Abstract

The performance of p–i–n planar perovskite solar cells (PSCs) strongly depends on the electronic structure and interfacial properties of hole transporting materials (HTMs). Four diphenylamine derivatives with a fluorene core were synthesized and employed as hole transport layers in inverted p–i–n planar PSCs. HTMs that are endowed with vinyl crosslinking units can form insoluble 3D networks under mild annealing temperature, which improve the solvent resistance during the device fabrication and morphological stability. Moreover, the optimized devices incorporating crosslinked HTMs exhibit an impressive power conversion efficiency of 18.7% with a high J_sc of 20.89 mA cm⁻², V_oc of 1.15 V and FF of 77.8%, which are superior to those of PEDOT:PSS based PSCs. The ultraviolet photoelectron spectroscopy measurement justifies that the new HTMs feature deep HOMO levels aligning well with the perovskite. Moreover, the hydrophobic nature of the synthesized HTMs favors the formation of large grained and continuous perovskite films with good surface coverage, evidenced by the water contact angles and film morphology measurements. Steady-state and time-resolved photoluminescence studies also reveal that fast charge transfer and suppressed recombination occur between the perovskite and HTMs. Our studies demonstrate that employing crosslinked organic HTMs is a promising approach to achieve high efficiency and stable PSCs.