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Three small molecules as front cell donors for tandem cells are thoroughly evaluated and a high power conversion efficiency of 11.47% is achieved, which demonstrates that the oligomer-like small molecules offer a good choice for high-performance tandem solar cells.

Organic–inorganic hybrid perovskites have cemented their position as an exceptional class of optoelectronic materials thanks to record photovoltaic efficiencies of 22.1%, as well as promising demonstrations of light-emitting diodes, lasers, and light-emitting transistors. Perovskite materials with photoluminescence quantum yields close to 100% and perovskite light-emitting diodes with external quantum efficiencies of 8% and current efficiencies of 43 cd A⁻¹ have been achieved. Although perovskite light-emitting devices are yet to become industrially relevant, in merely two years these devices have achieved the brightness and efficiencies that organic light-emitting diodes accomplished in two decades. Further advances will rely decisively on the multitude of compositional, structural variants that enable the formation of lower-dimensionality layered and three-dimensional perovskites, nanostructures, charge-transport materials, and device processing with architectural innovations. Here, the rapid advancements in perovskite light-emitting devices and lasers are reviewed. The key challenges in materials development, device fabrication, operational stability are addressed, and an outlook is presented that will address market viability of perovskite light-emitting devices.

Perovskites have sparked a revolution in photovoltaics, and their excellent optoelectronic properties hold the potential to trigger a similar advance in the field of light emission. The versatility of organic–inorganic hybrid perovskites as emitters and gain media is explored, device performance/architectures, processing conditions, and working mechanisms are analyzed, and the main barriers toward market viability are addressed.

Upconversion-perovskite nanohybrids are prepared by assembling CH₃NH₃PbBr₃ perovskite nanoparticles (PK) with naked NaYF₄:Yb³⁺,Tm³⁺ nanoparticles (UC_n) via an innovative strategy consisting of using cucurbit[7]uril (CB[7]) to anchor the perovskite nanoparticles firmly and closely to the upconversion nanoparticles, thus leading to UC_n@PK_CB nanohybrids. A commercial multiphoton laser scanning confocal microscope is used to demonstrate the successful assembly. This technique proves to be useful to evaluate luminescence lifetime in the range of several tens of μs and allows visualization of the extraordinarily efficient nontrivial resonance energy transfer from the upconversion nanoparticle to the perovskite after near-infrared (NIR) excitation of the nanohybrid as well as the homogeneity of the UC_n@PK_CB sample. The considerable photostability of the perovskite in these nanohybrids is demonstrated by prolonged irradiation of the nanohybrid under UV light as well as under NIR light.

Upconversion and perovskite nanoparticles are efficiently assembled by using the portals of cucurbit[7]uril to anchor the nanoparticles firmly and closely, as shown by the energy transfer efficiency to the perovskite nanoparticle after near-infrared excitation of the nanohybrid. A commercial multiphoton laser scanning confocal microscope allows the evaluation of the assembly and the verification of the homogeneity of the sample.

Graphdiyne, a novel large π-conjugated carbon hole transporting material, is employed as anode buffer layer in colloidal quantum dots solar cells. Power conversion efficiency is notably enhanced to 10.64% from 9.49% compared to relevant reference devices. Hole transfer from the quantum dot solid active layer to the anode can be appreciably enhanced only by using graphdiyne to lower the work function of the colloidal quantum dot solid. It is found that the all-carbon buffer layer prolongs the carrier lifetime, reducing surface recombination on the previously neglected back side of the photovoltaic device. Remarkably, the device also shows high long-term stability in ambient air. The results demonstrate that graphdiyne may have diverse applications in enhancing optoelectronic devices.

The novel large π-conjugated carbon hole transporting material, graphdiyne (GD) is used as anode buffer layer in PbS CQD solar cells. GD increases carrier lifetime and reduces carrier recombination inside the PbS CQD solar cells. Notably, a high power conversion efficiency of 10.64% is achieved, and the device also shows high long-term stability in ambient air.

Methylammonium bromide is used as an additive in the lead acetate-based precursor solution for perovskite solar cells by T. P. Russell, R. Zhu, and co-workers on page 3508. This is found to significantly improved perovskite film quality and optoelectronic properties. The optimized device delivers a power conversion efficiency of 18.3%, holding promise for highly efficient perovskite solar cells.

A dual-phase all-inorganic composite CsPbBr₃-CsPb₂Br₅ is developed and applied as the emitting layer in LEDs, which exhibited a maximum luminance of 3853 cd m^–2, with current density (CE) of ≈8.98 cd A^–1 and external quantum efficiency (EQE) of ≈2.21%, respectively. The parasite of secondary phase CsPb₂Br₅ nanoparticles on the cubic CsPbBr₃ nanocrystals could enhance the current efficiency by reducing diffusion length of excitons on one side, and decrease the trap density in the band gap on the other side. In addition, the introduction of CsPb₂Br₅ nanoparticles could increase the ionic conductivity by reducing the barrier against the electronic and ionic transport, and improve emission lifetime by decreasing nonradiative energy transfer to the trap states via controlling the trap density. The dual-phase all-inorganic CsPbBr₃-CsPb₂Br₅ composite nanocrystals present a new route of perovskite material for advanced light emission applications.

Dual-phase CsPbBr₃-CsPb₂Br₅ composites for all-inorganic perovskite light emitting diodes (LEDs) are fabricated, which exhibit significantly improved performance, representing a great increase in the CE and EQE, about 21- and 18-fold improvement than that of the best reported CsPbBr₃ LEDs. The dual-phase all-inorganic CsPbBr₃-CsPb₂Br₅ composite nanocrystals present a new route of perovskite material for advanced light emission applications.

Hybrid organic-inorganic perovskites have attracted considerable attention after promising developments in energy harvesting and other optoelectronic applications. However, further optimization will require a deeper understanding of the intrinsic photophysics of materials with relevant structural characteristics. Here, the dynamics of photoexcited charge carriers in large-area grain organic-inorganic perovskite thin films is investigated via confocal time-resolved photoluminescence spectroscopy. It is found that the bimolecular recombination of free charges is the dominant decay mechanism at excitation densities relevant for photovoltaic applications. Bimolecular coefficients are found to be on the order of 10⁻⁹ cm³ s⁻¹, comparable to typical direct-gap semiconductors, yet significantly smaller than theoretically expected. It is also demonstrated that there is no degradation in carrier transport in these thin films due to electronic impurities. Suppressed electron–hole recombination and transport that is not limited by deep level defects provide a microscopic model for the superior performance of large-area grain hybrid perovskites for photovoltaic applications.

The local dynamics of photoexcited charge carriers in “large-grain hybrid organic-inorganic perovskites” is presented. Under illumination conditions relevant for photovoltaics, a suppressed recombination of free carriers is observed where electronic impurities play a negligible role in the overall kinetics. This study provides a microscopic model for low defect large-grain hybrid perovskites where non-Langevin recombination results in superior photovoltaic performance.

A nonfullerene-based polymer solar cell (PSC) that significantly outperforms fullerene-based PSCs with respect to the power-conversion efficiency is demonstrated for the first time. An efficiency of >11%, which is among the top values in the PSC field, and excellent thermal stability is obtained using PBDB-T and ITIC as donor and acceptor, respectively.

The applications of organotin halide perovskites are limited because of their chemical instability under ambient conditions. Upon air exposure, Sn²⁺ can be rapidly oxidized to Sn⁴⁺, causing a large variation in the electronic properties. Here, the role of organic cations in degradation is investigated by comparing methylammonium tin iodide (MASnI₃) and formamidinium tin iodide (FASnI₃). Through chemical analyses and theoretical calculations, it is found that the organic cation strongly influences the oxidation of Sn²⁺ and the binding of H₂O molecules to the perovskite lattice. On the one hand, Sn²⁺ can be easily oxidized to Sn⁴⁺ in MASnI₃, and replacing MA with FA reduces the extent of Sn oxidation; on the other hand, FA forms a stronger hydrogen bond with H₂O than does MA, leading to partial expansion of the perovskite network. The two processes compete in determining the material's conductivity. It is noted that the oxidation is a difficult process to prevent, while the water effect can be largely suppressed by reducing the moisture level. As a result, FASnI₃-based conductors and photovoltaic cells exhibit much better reproducibility as compared to MASnI₃-based devices. This study sheds light on the development of stable Pb-free perovskite optoelectronic devices through new material design.

It is found that organic cation considerably influences the oxidation of Sn²⁺ and the binding of H₂O molecules to the perovskite lattice. Sn²⁺ can be easily oxidized to Sn⁴⁺ in MASnI₃, but not in FASnI₃. Solar cells fabricated from FASnI₃ demonstrate much improved reproducibility in device performance as compared to that from MASnI₃.

Organic–inorganic lead halide perovskites are emerging materials for the next-generation photovoltaics. Lead halides are the most commonly used lead precursors for perovskite active layers. Recently, lead acetate (Pb(Ac)₂) has shown its superiority as the potential replacement for traditional lead halides. Here, we demonstrate a strategy to improve the efficiency for the perovskite solar cell based on lead acetate precursor. We utilized methylammonium bromide as an additive in the Pb(Ac)₂ and methylammonium iodide precursor solution, resulting in uniform, compact and pinhole-free perovskite films. We observed enhanced charge carrier extraction between the perovskite layer and charge collection layers and delivered a champion power conversion efficiency of 18.3% with a stabilized output efficiency of 17.6% at the maximum power point. The optimized devices also exhibited negligible current density–voltage (J–V) hysteresis under the scanning conditions.

High-performance inverted perovskite solar cells based on lead acetate precursor are demonstrated with power conversion efficiency exceeding 18% and stabilized output efficiency of 17.6%. Methylammonium bromide was utilized as additive into the lead acetate precursor solutions, leading to the perovskite films with improved performance.

For realizing flexible perovskite solar cells (PSCs), it is important to develop low-temperature processable interlayer materials with excellent charge transporting properties. Herein, a novel polymeric hole-transport material based on 1,4-bis(4-sulfonatobutoxy)benzene and thiophene moieties (PhNa-1T) and its application as a hole-transport layer (HTL) material of high-performance inverted-type flexible PSCs are introduced. Compared with the conventionally used poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), the incorporation of PhNa-1T into HTL of the PSC device is demonstrated to be more effective for improving charge extraction from the perovskite absorber to the HTL and suppressing charge recombination in the bulk perovskite and HTL/perovskite interface. As a result, the flexible PSC using PhNa-1T achieves high photovoltaic performances with an impressive power conversion efficiency of 14.7%. This is, to the best of our knowledge, among the highest performances reported to date for inverted-type flexible PSCs. Moreover, the PhNa-1T-based flexible PSC shows much improved stability under an ambient condition than PEDOT:PSS-based PSC. It is believed that PhNa-1T is a promising candidate as an HTL material for high-performance flexible PSCs.

By incorporating low-temperature solution-processable 1,4-bis(4-sulfonatobutoxy)benzene and thiophene moieties polymer as a hole-transport layer, highly efficient, environmental stable, and mechanically flexible planar-heterojunction perovskite solar cell has been successfully achieved with an excellent power conversion efficiency of 14.7%.

Formamidinium lead iodide (FAPbI₃) has a broader absorption spectrum and better thermal stability than the most famous methylammonium lead iodide, thus exhibiting great potential for photovoltaic applications. In this report, the light-induced photoluminescence (PL) evolution in FAPbI₃ thin films is investigated. The PL intensity evolution is found to be strongly dependent on the atmosphere surrounding the samples. When the film is exposed to air, its photoluminescence intensity is enhanced more than 140 times after continuous ultraviolet laser illumination for 2 h, and the average lifetime is prolonged from 17 to 389 ns. The enhanced photoluminescence implies that the trap density is significantly reduced. The comparative study of the photoluminescence properties in air, nitrogen, and oxygen/helium environment suggests that moisture is important for the PL enhancement. This is explained in terms of moisture-assisted light-healing effect in FAPbI₃ thin films. With this study, a new method is demonstrated to increase and control the quality of hybrid perovskite thin films.

Laser healing perovskites: Photophysical properties of FAPbI₃ thin films under continuous UV illumination are investigated. Giant light-induced enhancement of the photoluminescence intensity is observed when the sample is exposed to air. It is demonstrated that moisture plays a critical role in the light-induced photoluminescence enhancement effect. Laser healing in air can become a way to improve the quality of perovskite thin films.

A room-temperature supersaturated recrystallization method is developed on page 2435 by H. Zeng and co-workers, to rapidly synthesize all-inorganic halide perovskite quantum dots with blue, green, and red luminescent quantum yields of 70–95% and line-widths less than 35 nm. The origins of the optical superiority are proposed to be the 40 meV exciton binding energy, surface self-passivation, and quantum-well band alignment, leading to promising potential in healthy lighting and wide-color-gamut displays.

On page 2426, C. P. Grigoropoulos, S. Kim, Y. K. Hong, and co-workers demonstrate a novel process architecture for flexible electronics. The multilayer molybdenum disulfide thin-film transistor array fabricated according to this scheme exhibits not only outstanding device performances, but also no apparent degradation under various mechanical stresses. These results could provide important applications in the fabrication of flexible integrated circuitry for various versatile functions.

2D perovskites is one of the proposed strategies to enhance the moisture resistance, since the larger organic cations can act as a natural barrier. Nevertheless, 2D perovskites hinder the charge transport in certain directions, reducing the solar cell power conversion efficiency. A nanostructured mixed-dimensionality approach is presented to overcome the charge transport limitation, obtaining power conversion efficiencies over 9%.