Rational Molecular Design of Indeno[1,2-b]quinoxaline-Based Passivators with Multifunctional Groups to Effectively Retard Recombination and Enhance Voc in Perovskite Solar Cells.

Three indeno[1,2-b]quinoxaline-based passivators (CQs) with different functionalities including ketone, malononitrile, nitrile, and amine were prepared and used as passivators in perovskite solar cells (PSCs). All of them exhibit good thermal stability, low cost, and ease of preparation. The variation in molecular geometries, in planar and spiro-shaped designs with appropriate functional groups, highlights a comparison between their passivation properities. The CQs can effectively passivate defects in the perovskite layer associated with unsaturated Pb2+ coordination. This leads to enhanced perovskite grain size, improved short-circuit current (Jsc), and reduced recombination, thereby increasing the open-circuit voltage (Voc) values of PSCs. The use of spiro-shaped CQ-Spiro as a passivator results in optimal performance, with Jsc of 24.72 mA∙cm-2, Voc of 1.14 V, fill factor of 0.76, and a corresponding overall conversion efficiency of 21.42% (compared to the control device with Spiro-OMeTAD, which has an efficiency of 18.1%). After 264 hours operation, the device can maintain 89.6% of original efficiency. It is demonstrated that spiro-shaped derivatives of CQ-Spiro containing multifunctional groups with Lewis base properties can provide another promising choice for passivators in PSCs.