Mitigating trap states in halide perovskite solar cells through the synergy of coordination, hydrogen and halogen types of bonding

Abstract

The growth regulation of polycrystalline perovskite films by the introduction of various additives has recently become a popular method for achieving superior efficiency and stability of perovskite solar cells. In the present work, a series of difluorobenzene derivatives were explored as additives to regulate the growth of perovskite crystalline films. Utilizing DFT calculations, NMR spectroscopy and X-ray photoelectron spectroscopy, we were able to describe the modulation of perovskite crystallization as related to the coordinating effect of the –CN groups and the synergistic effects induced by the hydrogen and halogen bonding. We discovered that the best additive in our study, 4-bromo-2,6-difluorobenzonitrile (BrFBN), has markedly improved perovskite film nanoscale morphology, suppressed non-radiative recombination, and enhanced the power conversion efficiency (PCE) of perovskite solar cells up to 24.42%. Additionally, the ambient and operational stability of the devices was significantly improved. According to the results of our density functional theory calculations, BrFBN can effectively passivate a variety of perovskite surfaces while outcompeting its own dimerization which explains the high affinity and effective availablity of BrFBN for passivating the perovskite surfaces. The present work provides a promising pathway towards obtaining stable high-performance perovskite solar cells via the use of additives enabling several types of synergistic interactions with the perovskite precursor components.