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Inorganic perovskites such as CsPbX3 (X=Cl, Br, I) have attracted attention due to their excellent thermal stability and high photoluminescence quantum efficiency. However, the electroluminescence quantum efficiency of their light-emitting diodes was <1%. We posited that this low efficiency was a result of high leakage current caused by poor perovskite morphology, high non-radiative recombination at interfaces and perovskite grain boundaries, and also charge injection imbalance. Here, we incorporated a small amount of methylammonium organic cation into the CsPbBr3 lattice and by depositing a hydrophilic and insulating polyvinyl pyrrolidine polymer atop the ZnO electron-injection layer to overcome these issues. As a result, we obtained light-emitting diodes exhibiting a high brightness of 91,000 cd m−2 and a high external quantum efficiency of 10.4% using a mixed-cation perovskite Cs0.87MA0.13PbBr3 as the emitting layer. To the best of our knowledge, this is the brightest and most-efficient green perovskite light-emitting diodes reported to date.

The tandem solar cell architecture is an effective way to harvest a broader part of the solar spectrum and make better use of the photonic energy than the single junction cell. Here, we present the design, synthesis, and characterization of a series of new low bandgap polymers specifically for tandem polymer solar cells. These polymers have a backbone based on the benzodithiophene (BDT) and diketopyrrolopyrrole (DPP) units. Alkylthienyl and alkylphenyl moieties were incorporated onto the BDT unit to form BDTT and BDTP units, respectively; a furan moiety was incorporated onto the DPP unit in place of thiophene to form the FDPP unit. Low bandgap polymers (bandgap = 1.4-1.5 eV) were prepared using BDTT, BDTP, FDPP, and DPP units via Stille-coupling polymerization. These structural modifications lead to polymers with different optical, electrochemical, and electronic properties. Single junction solar cells were fabricated, and the polymer:PC(71)BM active layer morphology was optimized by adding 1,8-diiodooctane (DIO) as an additive. In the single-layer photovoltaic device, they showed power conversion efficiencies (PCEs) of 3-6%. When the polymers were applied in tandem solar cells, PCEs over 8% were reached, demonstrating their great potential for high efficiency tandem polymer solar cells.

Perovskite light-emitting diodes (PeLEDs) have showed significant progress in recent years; the external quantum efficiency (EQE) of electroluminescence in green and red regions has exceeded 20%, but the efficiency in blue lags far behind. Here, a large cation CH 3 CH 2 NH 2 + is added in PEA 2 (CsPbBr 3) 2 PbBr 4 perovskite to decrease the Pb-Br orbit coupling and increase the bandgap for blue emission. X-ray diffraction and nuclear magnetic resonance results confirmed that the EA has successfully replaced Cs + cations to form PEA 2 (Cs 1-x EA x PbBr 3) 2 PbBr 4. This method modulates the photoluminescence from the green region (508 nm) into blue (466 nm), and over 70% photoluminescence quantum yield in blue is obtained. In addition, the emission spectra is stable under light and thermal stress. With configuration of PeLEDs with 60% EABr, as high as 12.1% EQE of sky-blue electroluminescence located at 488 nm has been demonstrated, which will pave the way for the full color display for the PeLEDs.

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Organic solar cells (OSCs) have attracted signifi cant attention as a clean and competitive renewable energy source due to their attractive features such as low-cost, light weight, solution processability and high mechanical fl exibility. [1][2][3][4] Benchmark power conversion effi ciencies (PCEs) of 10% or higher have been predicted if a suitable low bandgap donor material can be designed and implemented. [ 5 ] More recently, bulk heterojunction (BHJ) OSCs using solution-processed small molecules as the donor have attracted great attention. [6][7][8] This long-time but recently increased interest lies in the fact that solutionprocessed small molecule based OSCs have numerous advantages, such as relatively simple synthesis and purifi cation methods, monodispersity and well defi ned structures, high open circuit voltage and charge carrier mobilities, and better batch-to-batch reproducibility. [6][7][8] However, solution-processed small molecule OSCs have not met such high expectations as those of their polymeric counterparts due to their limited PCEs. In most cases, small molecule devices using solution processing always seem to have poorer fi lm quality than that of their polymeric counterparts in BHJ OSCs. [ 6 , 7 ] It is thus expected that better PCE could be achieved if the intrinsic poor fi lm quality and morphology in BHJ architecture could be improved. However, in order to achieve this, careful molecule design has to be carried out to address many factors simultaneously, including the material's solar light absorption associated with its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) positions, mobility, fi lm forming quality, electronic band structure and morphology compatibility with the acceptors, and so on. Indeed, several families of solution processed small molecules, such as oligothiophenes, [ 9 ] triarylamines, [ 10 , 11 ] diketopyrrolopyrroles (DPP), [ 12 ] squaraines, [ 13 , 14 ] merocyanine, [ 15 ] and dipyrromethene boron difl uoride (BODIPY) [ 16 ] derivatives, have offered great promise in this direction. Although still lower than the PCE of their polymeric counterparts ( ∼ 6-8%), [17][18][19][20][21] the highest published PCE of 4.4% for solution-processed small molecule/fullerene derivative based BHJ OSCs was recently achieved by a University of California Santa Barbara group using a DPP-thiophene derivative. [ 12 ] Push-pull chromophores involving electron-donating and electron-withdrawing groups have been widely investigated for OSC molecules. [ 8 ] This type of molecular architecture can lower the material bandgap and extend the absorption spectrum toward longer wavelengths, and at the same time, the HOMO and LUMO levels can be tuned effectively. [ 11 , 22 ] Oligothiophenes with well defi ned structures possess highly delocalized π -electrons along the molecular backbone and are well known as one of the most effective hole-transporting materials. Oligothiophenes with a push-pull structure have been widely investigated in solution processed ...

Hexagonal boron nitride (h-BN), an isomorph of graphene, has attracted great attention owing to its potential applications as an ultra-flat substrate or gate dielectric layer in novel graphene-based devices. Besides, h-BN appears to be a promising material for deep ultraviolet (DUV) optoelectronic applications because of its extraordinary physical properties, such as wide band gap and high absorption coefficient. In this work, two-dimensional h-BN with controllable layers was synthesized on Cu foils by ion beam sputtering deposition, and DUV photodetectors were fabricated from the transferred h-BN layers on SiO/Si substrates. The h-BN layers synthesized at the higher substrate temperature possess a lower density of domain boundaries and higher crystalline quality, and the photodetectors based on a 3 nm h-BN layer exhibited high performance with an on/off ratio of >10 under DUV light illumination at 212 nm and a cutoff wavelength at around 225 nm. This work demonstrates that two-dimensional h-BN layers are promising for the construction of high-performance solar-blind photodetectors.

We successfully demonstrated an integrated perovskite/bulk-heterojunction (BHJ) photovoltaic device for efficient light harvesting and energy conversion. Our device efficiently integrated two photovoltaic layers, namely a perovskite film and organic BHJ film, into the device. The device structure is ITO/TiO2/perovskite/BHJ/MoO3/Ag. A wide bandgap small molecule DOR3T-TBDT was used as donor in the BHJ film, and a power conversion efficiency (PCE) of 14.3% was achieved in the integrated device with a high short circuit current density (JSC) of 21.2 mA cm(-2). The higher JSC as compared to that of the traditional perovskite/HTL (hole transporting layer) device (19.3 mA cm(-2)) indicates that the BHJ film absorbs light and contributes to the current density of the device. Our result further suggests that the HTL in traditional perovskite solar cell, even with good light absorption capability, cannot contribute to the overall device photocurrent, unless this HTL becomes a BHJ layer (by adding electron transporting material like PC71BM).