Interface passivation treatment by halogenated low-dimensional perovskites for high-performance and stable perovskite photovoltaics

The voltage loss which is mainly caused by the nonradiative recombination at the interface has played a serious negative effect on the photovoltaic performance of perovskite solar cells (PSCs). Herein, we firstly designed four halogenated low-dimensional perovskite (LDP) capping layers by the way of employing different benzylammonium-based aromatic cations for high-performance devices. The introduction of halogen functional groups can not only enhance the hydrophobicity but also optimize the photovoltaic characteristics of LDP which play an important role on passivation effect of the interface between perovskite and hole transport materials (HTM) layer. The films with halogenated LDP passivation layers displayed suppressed nonradiative recombination and reduced trap density, leading to significantly reduced voltage loss. As a result, the optimal devices with 4-bromobenzylammonium-based LDP layer achieved the power conversion efficiency (PCE) as high as 21.13% with an enhanced open-circuit voltage (Voc) of 1.14 V. Under the hydrophobic and buffer action of the halogenated LDP layer, the modified devices showed outstanding long-term stability when exposed to moisture, heat and continuous UV irradiation. This work proves the enhanced passivation effect of LDP layer by regulating the chemical property of introduced organic cations for high-performance and stable perovskite photovoltaics.