Trade-off effect of hydrogen-bonded dopant-free hole transport materials on performance of inverted perovskite solar cells

Benefiting from their ordered orientation and superior stability compared to traditional conjugated materials, hydrogen bonding (HB)-induced H-aggregates in organic small molecule hole-transport materials (HTMs) hold a big potential for high-performance inverted perovskite solar cells (IPSCs). However, H-aggregates can also lead to excessive face-aggregation by forming the gaps between aggregates, which is in turn unfavorable for charge mobility and thus for the overall device performance. Herein, we design and synthesize a new set of HB-containing triphenylamine-based small molecules to tailor the degree of H-aggregation, namely O1 (without HB), O2 (unilateral HB unit), and O3 (bilateral HB units). These HTMs make a clear trade-off effect on the charge mobility within the HTM and the interfacial properties of perovskite and HTM. Although the interfacial hole extraction process is promoted upon the HB-functionalized interface, the best performance of IPSCs is still achieved by O1 HTM, which is mainly influenced by the higher hole mobility without HB-induced H-aggregates. Nevertheless, the photo stability of as-fabricated devices is effectively improved upon the HB passivation effect on the interface of HTM (O2 or O3) and perovskite, as well as the better quality of atop perovskite layers with less grain boundary compared to the reference case (O1).