Quinoxaline‐Based Materials That Exhibit a Significant Passivation Effect and Lead to the Enhancement in the Power Conversion Efficiency of Perovskite Solar Cells

The efficacy of three bifunctional organic materials, referred as quinoxaline‐based hole‐transporting materials (Qu‐HTMs) (quinoxaline‐based cyano [Qu‐CN], carboxylic acid [Qu‐COOH], and triphenylamine), is showcased in this study. These materials comprise a quinoxaline core, functionalized with carboxylic acid and nitrile as electron acceptors and triphenylamine as a donor. These Qu‐HTMs demonstrate excellent thermal stability and coplanarity, which facilitate a dense packing in an ordered arrangement. This can be attributed to the sulfur–sulfur interaction that promotes intermolecular attractions. In addition to passivating the coordination defects of Pb 2+ in the perovskite layer, Qu‐HTMs also enhance the charge mobility, short‐circuit current density ( J sc ), and open‐circuit voltage ( V oc ) of perovskite solar cells. The observations indicate that the annealing processes between the interface of Qu‐CN and perovskite, as well as Qu‐COOH and perovskite, lead to the formation of the α / δ phase on the surface of perovskite, which is advantageous for charge conduction. Using Qu‐CN as HTM and Qu‐COOH as a passivator in antisolvent showed the best performance, which exhibited a J sc of 23.36 mA cm −2 , a V oc of 1.09 V, and a fill factor of 0.802, corresponding to an overall conversion efficiency of 20.42% (cf. a control device 17.25% of 2,2′7,7′‐tetrakis( N , N ′‐di‐ p ‐methoxyaniline)‐9,9′‐spirobifluorene). After 480 h operation, the device can maintain 70% of original efficiency.