Metal halide perovskite materials are emerging solution-processed semiconductors with considerable promise in optoelectronic devices 1,2 . Metal halide perovskite-based light-emitting devices (pLEDs) have received extensive interest for applications in flat-panel displays and solid-state lighting owing to their promise of low cost, tunable colors with narrow emission bandwidths, high photoluminescence quantum yield (PLQY), and facile solution processing [3][4][5][6][7] .However, the highest reported external quantum efficiency (EQE) of green-and red-emitting pLEDs are 14.36% 6,8 and 11.7% 7 , still far behind the performance of organic LEDs (OLEDs) [9][10][11] and inorganic quantum dot LEDs (QLEDs) 12 . Here we report visible perovskite LEDs that

Recently, low-bandgap formamidinium lead iodide FAPbI 3 -based perovskites are of particular interest for highperformance perovskite solar cells (PSCs) due to their broad spectral response and high photocurrent output. However, to inhibit the spontaneous α-to-δ phase transition, 15−17% (molar ratio) of bromide and cesium or methylammonium incorporated into the FAPbI 3 are indispensable to achieve efficient PSCs. In return, the high bromide content will increase bandgap and narrow the spectral response region. If simply reducing the bromide content, the corresponding PSCs exhibit inferior operational stability due to α-toδ phase transition, interface degradation, and halide migration. Herein, we report a CsPbBr 3 -cluster assisted vertically bottom-up crystallization approach to fabricate low-bromide (1% ∼ 6%), αphase pure, and MA-free FAPbI 3 -based PSCs. The clusters, in the size of several nanometers, could act as nuclei to facilitate vertical growth of high quality α-FAPbI 3 perovskite crystals. Moreover, these clusters can show further intake by perovskite after thermal annealing, which improves the phase homogeneity of the as-prepared perovskite films. As a result, the corresponding mesoporous PSCs deliver a champion efficiency of 21.78% with photoresponse extended to 830 nm. Moreover, these devices show remarkably improved operational stability, retaining ∼82% of the initial efficiency after 1,000 h of maximum power point tracking under 1 sun condition.

Recently, surface passivation has been proved to be an essential approach for obtaining efficient and stable perovskite light-emitting diodes (Pero-LEDs). Phosphine oxides performed well as passivators in many reports. However, the most commonly used phosphine oxides are insulators, which may inhibit carrier transport between the perovskite emitter and charge-transporter layers, limiting the corresponding device performance. Here, 2,7-bis­(diphenylphosphoryl)-9,9′-spirobifluorene (SPPO13), a conductive molecule with two phosphine oxide functional groups, is introduced to modify the perovskite emitting layer. The bifunctional SPPO13 can passivate the nonradiative defects of perovskite and promote electron injection at the interface of perovskite emitter and electron-transporter layers. As a result, the corresponding Pero-LEDs obtain a maximum external quantum efficiency (EQE) of 22.3%. In addition, the Pero-LEDs achieve extremely high brightness with a maximum of around 190 000 cd/m2.

All‐inorganic and lead‐free CsSnI3 is emerging as one of the most promising candidates for near‐infrared perovskite light‐emitting diodes (NIR Pero‐LEDs), which find practical applications including facial recognition, biomedical apparatus, night vision camera, and Light Fidelity. However, in the CsSnI3‐based Pero‐LEDs, the holes injection is significantly higher than that of electrons, resulting in unbalanced charge injection, undesired exciton dissipation, and poor device performance. Herein, it is proposed to manage charge injection and recombination behavior by tuning the interface area of perovskite and charge‐transporter. A dendritic CsSnI3 structure is prepared on the hole‐transporter, only making a bottom contact with the hole‐transporter and exposing all other available crystal surfaces to the electron‐transporter. In other words, the interface area of perovskite/electron‐transporter is significantly higher than that of perovskite/hole‐transporter. Moreover, the embedding interface of perovskite/electron‐transporter can spatially confine holes and electrons, increasing the radiation recombination. By taking advantage of the dendritic structure, efficient lead‐free NIR Pero‐LEDs are achieved with a record external quantum efficiency (EQE) of 5.4%. More importantly, the dendritic structure shows great superiorities in flexible devices, for there is almost no morphology change after 2000‐cycles of bends, and the fabricated Pero‐LEDs can keep 93.4% of initial EQEs after 50‐cycles of bends.

Fullerene derivatives, especially after purposely functionalization, have potential to efficiently passivate interfacial defects between perovskites and electron transport layers. In this work, a fullerene derivative with amine functional group, 2,5‐diphenyl C60 fulleropyrrolidine (DPC60), is synthesized and employed as an interfacial layer between a perovskite and SnO2 in planar perovskite solar cells (PSCs). The cis‐configuration and the specific amine group of DPC60 effectively enhance the chemical interaction between the perovskite and DPC60, promoting the passivation of perovskite defects at the interface. The suitable energy level of DPC60 and the improved conductivity of the SnO2/DPC60 film facilitate the electron extraction from the perovskite layer. As a result, PSCs incorporated with DPC60 reach a PCE of 20.4% with high reproducibility, which is much higher than that of the bare SnO2 based devices (18.8%). Furthermore, the hydrophobic DPC60 layer suppresses heterogeneous nucleation and improves the crystallinity of the perovskite film, resulting in better device stability, retaining 82% of its initial efficiency after 200 h of 1 sun continuous irradiation and thermal ageing (55 ± 5 °C).

Exciton–phonon interaction in quasi-2D material was investigated. It was shown that longitudinal optical phonon, rather than acoustic phonon-exciton coupling dominated the enhancement of exciton–phonon coupling strength.

The inorganic CuSCN interlayer makes carbon-based perovskite solar cells more efficient and stable.

Recently, metal halide perovskite light‐emitting diodes (Pero‐LEDs) have achieved significant improvement in device performance, especially for external quantum efficiency (EQE). And EQE is mostly determined by internal quantum efficiency of the emitting material, charge injection balancing factor (ηc), and light extraction efficiency (LEE) of the device. Herein, an ultrathin poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (UT‐PEDOT:PSS) hole transporter layer is prepared by a water stripping method, and the UT‐PEDOT:PSS can enhance ηc and LEE simultaneously in Pero‐LEDs, mostly due to the improved carrier mobility, more matched energy level alignment, and reduced photon loss. More importantly, the performance enhancement from UT‐PEDOT:PSS is quite universal and applicable in different kinds of Pero‐LEDs. As a result, the EQEs of Pero‐LEDs based on 3D, quasi‐3D, and quasi‐2D perovskites obtain enhancements of 42%, 87%, and 111%, and the corresponding maximum EQE reaches 17.6%, 15.0%, and 6.8%, respectively.