Halide perovskite materials offer an ideal playground for easily tuning their color and, accordingly, the spectral range of their emitted light. In contrast to common procedures, this work demonstrates that halide substitution in Ruddlesden–Popper perovskites not only progressively modulates the bandgap, but it can also be a powerful tool to control the nanoscale phase segregation—by adjusting the halide ratio and therefore the spatial distribution of recombination centers. As a result, thin films of chloride‐rich perovskite are engineered—which appear transparent to the human eye—with controlled tunable emission in the green. This is due to a rational halide substitution with iodide or bromide leading to a spatial distribution of phases where the minor component is responsible for the tunable emission, as identified by combined hyperspectral photoluminescence imaging and elemental mapping. This work paves the way for the next generation of highly tunable transparent emissive materials, which can be used as light‐emitting pixels in advanced and low‐cost optoelectronics.
Defect‐mediated recombination losses limit the open‐circuit voltage (VOC) of perovskite solar cells (PSCs), negatively affecting the device's performance. Bulk and dimensional engineering have both been reported as promising strategies to passivate shallow defects, thus improving the photovoltaic conversion efficiency (PCE). Here, a combined bulk and surface treatment employing chlorine‐based compounds is employed. Methylammonium chloride (MACl) is used as a bulk additive, while 4‐methylphenethylammonium chloride (MePEACl) is deposited onto the perovskite surface to produce a low‐dimensional perovskite (LDP) and reduce nonradiative recombination. Through structural and morphological investigations, it can be confirmed that bulk and surface doping have a beneficial effect on the film morphology and its overall quality, while electroluminescence (EL) and photoluminescence (PL) analyses demonstrate an increased and more homogeneous emission. Applying this double passivation strategy in PSC fabrication, a boost is observed in both the short‐circuit current density and the VOC of the devices, achieving a champion 21.4% PCE while improving device stability.
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