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

Abstract

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 Pb2+ in the perovskite layer, Qu-HTMs also enhance the charge mobility, short-circuit current density (Jsc), and open-circuit voltage (Voc) 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 Jsc of 23.36 mA cm−2, a Voc 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.