Potassium halides have recently garnered much attention, due to their improvement of perovskite solar cell performance. A small amount of potassium halide incorporated in a perovskite absorber is able to provide advantages in terms of crystallinity, light absorption and trap state reduction. Here, we present a potassium chloride (KCl) pretreatment process to fabricate high-efficiency perovskite solar cells (PSCs). A KCl layer was inserted at the SnO₂/MAPbI_3−xCl_x interface via a simple spin coating method. It is observed that potassium cations (K⁺) and chloride anions (Cl⁻) diffused into the perovskite film during the thermal annealing process. The diffusion of K⁺ and Cl⁻ will stop when they reach a bulk defect, resulting in an active passivation effect. It is verified that the incorporation of KCl enhances the crystal perfection and light absorption of the perovskite film. The average power conversion efficiency (PCE) of PSCs increases from 16.62% to 17.81%, with a leading PCE of 19.44%.

The purpose of this research was to understand the effect of a built-in ferroelectric field on the performance of two-dimensional (2D) lead-free perovskite material-based phototransistor applications. In this work, ferroelectric polymer poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) and two-dimensional (2D) lead-free perovskite ((C₆H₅C₂H₄NH₃)₂SnI₄) were utilized as a dielectric layer and a channel layer, respectively. We observed that large hysteresis was successfully eliminated in the transfer curve, as well as the subthreshold swing being significantly reduced by one order of magnitude after P(VDF-TrFE) was introduced as a dielectric layer. Under polarization “up” and “down” states, the device achieved a high photo-switching on/off ratio (>100) and a short photoresponse time (50 ms), respectively. In addition to that, the device also demonstrated a high responsivity of 14.57 A W⁻¹ and a high detectivity of 1.74 × 10¹² Jones under the polarization “up” state with an illumination intensity of 21 μW cm⁻². In addition, low temperature solution-processed P(VDF-TrFE) and (C₆H₅C₂H₄NH₃)₂SnI₄ (except for the contacts of Au electrodes) in this work are considered to be suitable and compatible for flexible-based phototransistor applications in the future.

A facile acetic acid modification is introduced to passivate the defects at the SnO ₂ /perovskite interface, thus improving the device performance.

The trap states at the interface between perovskite and charge-transport layer have a great influence on the performance of perovskite solar cells. Here, a high efficiency MAPbI_3−xCl_x perovskite solar cell has been demonstrated, by introducing a thin layer of LiF or PbF₂ between the SnO₂/perovskite. Improved charge collection and reduced interfacial charge recombination are realized, leading to remarkable rises of both open-circuit voltage (V_oc) and short-circuit current (J_sc). This successful interfacial passivation paved a new way to fabricate high performance perovskite solar cells with large V_oc.