Ligang Yuan

Photonic nanostructures are created in organo-metal halide perovskites by thermal nanoimprint lithography at a temperature of 100 °C. The imprinted layers are significantly smoothened compared to the initially rough, polycrystalline layers and the impact of surface defects is substantially mitigated upon imprint. As a case study, 2D photonic crystals are shown to afford lasing with ultralow lasing thresholds at room temperature.

Vacuum-sublimed inorganic cesium lead halide perovskite thin films are prepared and integrated in all-vacuum-deposited solar cells. Special care is taken to determine the stoichiometric balance of the sublimation precursors, which has great influence on the device performance. The mixed halide devices exhibit exceptional stabilized power conversion efficiency (11.8%) and promising thermal and long-term stabilities.

To increase the range of light absorption in polymer solar cells, two absorber donor polymers (blue and red, respectively) are utilized. In article 1604603, H. Ade and co-workers mix these polymers separately with a fullerene acceptor (grey) and process them using a new deposition strategy to create sequentially cast ternary (SeCaT) polymer solar cells that exhibit a bilayer structure without an interlayer.

Fully solution-processed direct perovskite solar cells with a planar junction are realized by incorporating a cross-linked [6,6]-phenyl-C61-butyric styryl dendron ester layer as an electron extracting layer. Power conversion efficiencies close to 19% and an open-circuit voltage exceeding 1.1 V with negligible hysteresis are delivered. A perovskite film with superb optoelectronic qualities is grown, which reduces carrier recombination losses and hence increases V _oc.

While indirectly patterned organic–inorganic hybrid perovskite nanostructures have been extensively studied for use in perovskite optoelectronic devices, it is still challenging to directly pattern perovskite thin films because perovskite is very sensitive to polar solvents and high-temperature environments. Here, a simple and low-cost approach is proposed to directly pattern perovskite solid-state films into periodic nanostructures. The approach is basically perovskite recrystallization through phase transformation with the presence of a periodic mold on an as-prepared solid-state perovskite film. Interestingly, this study simultaneously achieves not only periodically patterned perovskite nanostructures but also better crystallized perovskites and improved optical properties, as compared to its thin film counterpart. The improved optical properties can be attributed to the light extraction and increased spontaneous emission rate of perovskite gratings. By fabricating light-emitting diodes using the periodic perovskite nanostructure as the emission layers, approximately twofold higher radiance and lower threshold than the reference planar devices are achieved. This work opens up a new and simple way to fabricate highly crystalline and large-area perovskite periodic nanostructures for low-cost production of high-performance optoelectronic devices.

A new and simple direct nanopatterning approach for fabricating highly crystalline and large-area periodic perovskite nanostructures is proposed. This approach is suitable for preparing perovskite nanostructures with different configurations. More importantly, the prepared periodic perovskite nanostructures can be fabricated into different optoelectronic devices, such as solar cells, light-emitting diodes, laser diodes, and photodetectors.

A new, easy, and efficient approach is reported to enhance the driving force for charge transfer, break tradeoff between open-circuit voltage and short-circuit current, and simultaneously achieve very small energy loss (0.55 eV), very high open-circuit voltage (>1 V), and very high efficiency (>10%) in fullerene-free organic solar cells via an energy driver.

Nonfullerene polymer solar cells (PSCs) are fabricated with a perylene monoimide-based n-type wide-bandgap organic semiconductor PMI-F-PMI as an acceptor and a bithienyl-benzodithiophene-based wide-bandgap copolymer PTZ1 as a donor. The PSCs based on PTZ1:PMI-F-PMI (2:1, w/w) with the treatment of a mixed solvent additive of 0.5% N-methyl pyrrolidone and 0.5% diphenyl ether demonstrate a very high open-circuit voltage (V_oc) of 1.3 V with a higher power conversion efficiency (PCE) of 6%. The high V_oc of the PSCs is a result of the high-lying lowest unoccupied molecular orbital (LUMO) of −3.42 eV of the PMI-F-PMI acceptor and the low-lying highest occupied molecular orbital (HOMO) of −5.31 eV of the polymer donor. Very interestingly, the exciton dissociation efficiency in the active layer is quite high, even though the LUMO and HOMO energy differences between the donor and acceptor materials are as small as ≈0.08 and 0.19 eV, respectively. The PCE of 6% is the highest for the PSCs with a V_oc as high as 1.3 V. The results indicate that the active layer based on PTZ1/PMI-F-PMI can be used as the front layer in tandem PSCs for achieving high V_oc over 2 V.

Nonfullerene polymer solar cells with PTZ1 as a donor and PMI-F-PMI as an acceptor demonstrate a very high open-circuit voltage (V_oc) of 1.3 V with a higher power conversion efficiency of 6%. The high V_oc is a result of the high-lying lowest unoccupied molecular orbital (LUMO) of −3.42 eV of the PMI-F-PMI acceptor and the low-lying highest occupied molecular orbital (HOMO) of −5.31 eV of the polymer donor.

While SnPb alloyed perovskites have been considered as an effective approach to broaden the absorption spectrum, it is still challenging to modify the crystallization (and thus morphology, crystallinity, and orientation) in a controllable manner and thus boost the efficiency of SnPb alloyed perovskite solar cells. Here, it is unveiled that controlling the crystallization of CH₃NH₃Sn_0.25Pb_0.75I₃ films can be simply realized by adjusting the amount of dimethyl sulfoxide in precursors, which has not been reported in SnPb alloyed perovskite systems. The remarkable perovskite crystallinity enhancement by the 20-fold enhanced (110) plane intensity in the X-ray diffraction spectrum of CH₃NH₃Sn_0.25Pb_0.75I₃ and the preferred (110) orientation with the texture coefficient enhanced by 2.6 times to reach 0.88 are demonstrated. Importantly, it is discovered that the introduction of dimethyl sulfoxide avoids the formation of the colloidal coagulation observed in prolonged-storage precursors and ameliorates inhomogeneous Sn/Pb distributions in resultant perovskite films. Through optimizing perovskite films and device structures, hysteresis-free planar-heterojunction CH₃NH₃Sn_0.25Pb_0.75I₃ solar cells with the efficiency reaching 15.2%, which are the most efficient SnPb alloy-based perovskite solar cells, are achieved.

CH₃NH₃Sn_0.25Pb_0.75I₃ films with enhanced crystallinity, preferred orientation, and ameliorated inhomogeneous Sn/Pb distributions are realized by the controllable crystallization via the introduction of dimethyl sulfoxide. Optimized planar-heterojunction CH₃NH₃Sn_0.25Pb_0.75I₃-based solar cells achieve the power conversion efficiency of 15.2% and no hysteresis, which is the highest value among SnPb alloy-based perovskite solar cells.