Role of π-conjugated-length-regulated perovskite intergrain interconnecting in the photovoltaic performance of perovskite solar cells

Despite great advancements in perovskite solar cells (PSCs), the unsatisfactory intergrain interconnecting in polycrystalline perovskite films remains a challenge to be addressed. Herein, three bilateral dicarboxyic acids, i.e. suberic acid (SA), p-phthalic acid (PTA) and biphenyl dicarboxylic acid (BPDA), are employed as additives to uncover the role of π-conjugated-length-regulated intergrain interconnecting in PSCs. Benefiting from strong interactions between two-sided carboxyl groups and perovskites, incorporation of these additives can control crystal growth, passivate defects/traps and tighten the interconnecting of perovskite grains. Moreover, thanks to the large π-electron delocalization and π-π interactions, introduction of π-conjugated additives (i.e. PTA and BPDA) can evidently intensify the preferred orientation of perovskite crystals and improve the carrier transport between perovskite grains. Especially, by extending π-conjugated structure to biphenyl groups (i.e. BPDA), high-quality perovskite films exhibiting large and ordered grains with vertically columnar alignment, along with strong electrical intergrain interconnecting, are obtained. Moreover, the intrinsic hydrophobicity nature of π-conjugated structures is helpful for improving the moisture stability. Eventually, the champion efficiency of 20.87% is acquired with negligible hysteresis and excellent moisture stability for PSCs with BPDA. Our work demonstrates that the π-conjugated length of additives can play a vital role in regulating the intergrain interconnecting.