The passivation of defects at perovskite grain boundaries (GB) is crucial in achieving highly efficient and stable perovskite solar cells. Unlike the widely used additive passivation method where a mixture of additives and perovskite precursor is used for preparing perovskite films, we herein developed a new defect post-healing method via dip-coating trioctylphosphine oxide (TOPO) ligands on pre-fabricated carbon-based mesoscopic perovskite solar cells (MPSCs). Since perovskites have formed before post-healing, TOPO ligands are selectively adsorbed onto the exposed perovskite surface and hence have little influence on charge extraction of interfaces. The defects are post-healed via O atoms in PO bonds coordinated to halide-deficient sites, leading to an enhancement of the power conversion efficiency (PCE) from 11.0% to 12.8%. Moreover, due to the three hydrophobic long chain alkyls in TOPO, the humidity stability of the device has also been improved simultaneously.

Single component nanocrystals (NCs) with white fluorescence are promising single layer color conversion media for white light-emitting diodes (LED) because the undesirable changes of chromaticity coordinates for the mixture of blue, green and red emitting NCs can be avoided. However, their practical applications have been hindered by the relative low photoluminescence (PL) quantum yield (QY) for traditional semiconductor NCs. Though Mn-doped perovskite nanocube is a potential candidate, it has been unable to realize a white-light emission to date. In this work, the synthesis of Mn-doped 2D perovskite-related CsPb₂Cl_xBr_5−x nanoplatelets with a pure white emission from a single component is reported. Unlike Mn-doped perovskite nanocubes with insufficient energy transfer efficiency, the current reported Mn-doped 2D perovskite-related CsPb₂Cl_xBr_5−x nanoplatelets show a 10 times higher energy transfer efficiency from perovskite to Mn impurities at the required emission wavelengths (about 450 nm for perovskite emission and 580 nm for Mn emission). As a result, the Mn/perovskite dual emission intensity ratio surprisingly elevates from less than 0.25 in case of Mn-doped nanocubes to 0.99 in the current Mn-doped CsPb₂Cl_xBr_5−x nanoplatelets, giving rise to a pure white light emission with Commission Internationale de l'Eclairage (CIE) color coordinates of (0.35, 0.32). More importantly, the highest PL QY for Mn-doped perovskite-related CsPb₂Cl_xBr_5−x nanoplatelets is up to 49%, which is a new record for white-emitting nanocrystals with single component. These highly luminescent nanoplatelets can be blended with polystyrene (PS) without changing the white light emission but dramatically improving perovskite stability. The perovskite-PS composites are available not only as a good solution processable coating material for assembling LED, but also as a superior conversion material for achieving white light LED with a single conversion layer.