Chen Weijie

Lead halide perovskite quantum dots (QDs) possess color-tunable and narrow-band emissions and are very promising for lighting and display applications, but they suffer from lead toxicity and instability. Although lead-free Bi-based and Sn-based perovskite QDs (CsSnX₃, Cs₂SnX₆, and (CH₃NH₃)₃Bi₂X₉) are reported, they all show low photoluminescence quantum yield (PLQY) and poor stability. Here, the synthesis of Cs₃Bi₂Br₉ perovskite QDs with high PLQY and excellent stability is reported. Via a green and facile process using ethanol as the antisolvent, as-synthesized Cs₃Bi₂Br₉ QDs show a blue emission at 410 nm with a PLQY up to 19.4%. The whole series of Cs₃Bi₂X₉ (X = Cl, Br, and I) QDs by mixing precursors can cover the photoluminescence emission range from 393 to 545 nm. Furthermore, Cs₃Bi₂Br₉ QDs show excellent photostability and moisture stability due to the all-inorganic nature and the surface passivation by BiOBr, which enables the one-pot synthesis of Cs₃Bi₂Br₉ QD/silica composite. A lead-free perovskite white light-emitting diode is fabricated by simply combining the composite of Cs₃Bi₂Br₉ QD/silica with Y₃Al₅O₁₂ phosphor. As a new member of lead-free perovskite QDs, Cs₃Bi₂Br₉ QDs open up a new route for the fabrication of optoelectronic devices due to their excellent stability and photophysical characteristics.

A simple and environmentally benign synthetic method, combined with good crystallization, high photoluminescence quantum yields in the blue wavelength region, and excellent moisture stability, makes Cs₃Bi₂Br₉ quantum dots (QDs) very competitive for various optoelectronic applications. Finally, the first lead-free perovskite white light-emitting diode is successfully made by simply combining the composite of Cs₃Bi₂Br₉ QD/silica with Y₃Al₅O₁₂ phosphor.

High pressure (HP) can drive the direct sintering of nanoparticle assemblies for Ag/Au, CdSe/PbS nanocrystals (NCs). Instead of direct sintering for the conventional nanocrystals, this study experimentally observes for the first time high-pressure-induced comminution and recrystallization of organic–inorganic hybrid perovskite nanocrystals into highly luminescent nanoplates with a shorter carrier lifetime. Such novel pressure response is attributed to the unique structural nature of hybrid perovskites under high pressure: during the drastic cubic–orthorhombic structural transformation at ≈2 GPa, (301) the crystal plane fully occupied by organic molecules possesses a higher surface energy, triggering the comminution of nanocrystals into nanoslices along such crystal plane. Beyond bulk perovskites, in which pressure-induced modifications on crystal structures and functional properties will disappear after pressure release, the pressure-formed variants, i.e., large (≈100 nm) and thin (<10 nm) perovskite nanoplates, are retained and these exhibit simultaneous photoluminescence emission enhancing (a 15-fold enhancement in the photoluminescence) and carrier lifetime shortening (from ≈18.3 ± 0.8 to ≈7.6 ± 0.5 ns) after releasing of pressure from 11 GPa. This pressure-induced comminution of hybrid perovskite NCs and a subsequent amorphization–recrystallization treatment offer the possibilities of engineering the advanced hybrid perovskites with specific properties.

High pressure (up to tens of gigapascals), as a clean and powerful tool, can effectively alter crystal structures. It is experimentally investigated for the first time whether pressure can regulate the comminution and recrystallization of MAPbBr₃ nanocrystals. The initial nanocrystals slide into nanoslices during phase transformation to the orthorhombic polymorph, followed by recrystallization into nanoplates upon amorphization.

A facile methodology for the large-scale production of layer-controlled MoS₂ layers on an inexpensive substrate involving a simple coating of single source precursor with subsequent roll-to-roll-based thermal decomposition is developed. The resulting 50 cm long MoS₂ layers synthesized on Ni foils possess excellent long-range uniformity and optimum stoichiometry. Moreover, this methodology is promising because it enables simple control of the number of MoS₂ layers by simply adjusting the concentration of (NH₄)₂MoS₄. Additionally, the capability of the MoS₂ for practical applications in electronic/optoelectronic devices and catalysts for hydrogen evolution reaction is verified. The MoS₂-based field effect transistors exhibit unipolar n-channel transistor behavior with electron mobility of 0.6 cm² V⁻¹ s⁻¹ and an on-off ratio of ≈10³. The MoS₂-based visible-light photodetectors are fabricated in order to evaluate their photoelectrical properties, obtaining an 100% yield for active devices with significant photocurrents and extracted photoresponsivity of ≈22 mA W⁻¹. Moreover, the MoS₂ layers on Ni foils exhibit applicable catalytic activity with observed overpotential of ≈165 mV and a Tafel slope of 133 mV dec⁻¹. Based on these results, it is envisaged that the cost-effective methodology will trigger actual industrial applications, as well as novel research related to 2D semiconductor-based multifaceted applications.

A facile methodology for the large-scale production of layer-controlled MoS₂ layers on an inexpensive substrate implemented with subsequent two-step roll-to-roll-based thermal decomposition is developed. The resulting 50 cm long MoS₂ layers synthesized on Ni foils possess excellent long-range uniformity. This methodology is a promising way for simple control of the number of MoS₂ layers by adjusting the concentration of (NH₄)₂MoS₄.

Nonfullerene acceptors (NFAs) in blends with highly crystalline donor polymers have been shown to yield particularly high device voltage outputs, but typically more modest quantum yields for photocurrent generation as well as often lower fill factors (FF). In this study, we employ transient optical and optoelectronic analysis to elucidate the factors determining device photocurrent and FF in blends of the highly crystalline donor polymer PffBT4T-2OD with the promising NFA FBR or the more widely studied fullerene acceptor PC₇₁BM. Geminate recombination losses, as measured by ultrafast transient absorption spectroscopy, are observed to be significantly higher for PffBT4T-2OD:FBR blends. This is assigned to the smaller LUMO-LUMO offset of the PffBT4T-2OD:FBR blends relative to PffBT4T-2OD:PC₇₁BM, resulting in the lower photocurrent generation efficiency obtained with FBR. Employing time delayed charge extraction measurements, these geminate recombination losses are observed to be field dependent, resulting in the lower FF observed with PffBT4T-2OD:FBR devices. These data therefore provide a detailed understanding of the impact of acceptor design, and particularly acceptor energetics, on organic solar cell performance. Our study concludes with a discussion of the implications of these results for the design of NFAs in organic solar cells.

Charge separation and recombination dynamics in relation to film morphology and energetics are reported in nonfullerene-based PffBT4T-2OD:FBR solar cell. PffBT4T-2OD shows efficient exciton diffusion to the interface between the electron donors and the acceptors. Its small energetic offset explains relatively lower current density and fill factor correlated with geminated recombination and field-dependent photogeneration.

Comparing to other carbon materials, the general graphyne structure is much superior in terms of adaptable bandgap, uniformly distributed pores, more design flexibility, easier for chemical synthesis, pliable electronic properties, and smaller atomic density. Herein, novel γ-graphdiyne quantum dots (GD QDs) are used in perovskite solar cells as a surface modifier or dopant to TiO₂, CH₃NH₃PbI₃, and Spiro-OMeTAD to realize multiple advantageous effects, in hoping that it would form a more effective carrier transport channel for boosted solar cell performance. First, the presence of GD QDs on TiO₂ surface increases perovskite grain size for higher current density and fill factor. Second, the GD QDs at each interface reduce the conduction band offset, passivate the surface for suppressed carrier recombination to attain higher open-circuit voltage. Third, it improves hydrophobicity and eliminates pinholes in the Spiro-OMeTAD film for enhanced solar cell stability. As a result, the optimized device shows >15% enhancement in power conversion efficiency (from 17.17 to 19.89%) comparing to the reference device. More significantly, the device stability was improved in harsh environment (moist air, UV irradiation, or thermal conditions). It is expected that GD QDs will find their applications in efficient and stable perovskite solar cells and optoelectronic devices.

Controlling the morphology, surface passivation, and energy level in perovskite solar cells is paramount in obtaining optimal and stable optoelectronic properties. This study incorporates multifunctional γ-graphdiyne quantum dots in perovskite solar cells, which simultaneously induce an optimized morphology, surface passivation, conduction band offset, etc., resulting in enhancement of all photovoltaic parameters and stability in harsh environments.

Naphtho[1,2-b:5,6-b′]dithiophene is extended to a fused octacyclic building block, which is end capped by strong electron-withdrawing 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile to yield a fused-ring electron acceptor (IOIC2) for organic solar cells (OSCs). Relative to naphthalene-based IHIC2, naphthodithiophene-based IOIC2 with a larger π-conjugation and a stronger electron-donating core shows a higher lowest unoccupied molecular orbital energy level (IOIC2: −3.78 eV vs IHIC2: −3.86 eV), broader absorption with a smaller optical bandgap (IOIC2: 1.55 eV vs IHIC2: 1.66 eV), and a higher electron mobility (IOIC2: 1.0 × 10⁻³ cm² V⁻¹ s⁻¹ vs IHIC2: 5.0 × 10⁻⁴ cm² V⁻¹ s⁻¹). Thus, IOIC2-based OSCs show higher values in open-circuit voltage, short-circuit current density, fill factor, and thereby much higher power conversion efficiency (PCE) values than those of the IHIC2-based counterpart. In particular, as-cast OSCs based on FTAZ: IOIC2 yield PCEs of up to 11.2%, higher than that of the control devices based on FTAZ: IHIC2 (7.45%). Furthermore, by using 0.2% 1,8-diiodooctane as the processing additive, a PCE of 12.3% is achieved from the FTAZ:IOIC2-based devices, higher than that of the FTAZ:IHIC2-based devices (7.31%). These results indicate that incorporating extended conjugation into the electron-donating fused-ring units in nonfullerene acceptors is a promising strategy for designing high-performance electron acceptors.

A novel fused-ring electron acceptor (IOIC2) based on naphthodithiophene is designed and synthesized, and compared with a naphthalene-based counterpart (IHIC2). The IOIC2-based single-junction binary-blend organic solar cells exhibit efficiencies up to 12.3%, much higher than that of IHIC2 (7.45%).

In article number 1701305, Maria Antonietta Loi and co-workers show that the electron transport capability of the electron-extracting layer dominates the temperature dependence of the performance of hybrid perovskite solar cells. The authors further demonstrate efficient hybrid perovskite solar cells over a temperature range from 295 K to 160 K by n-doping the PCBM electron-extracting layer or using a fullerene derivative with intrinsically higher electron transport capability.

Flexible and semitransparent organic solar cells (OSCs) have been regarded as the most promising photovoltaic devices for the application of OSCs in wearable energy resources and building-integrated photovoltaics. Therefore, the flexible and semitransparent OSCs have developed rapidly in recent years through the synergistic efforts in developing novel flexible bottom or top transparent electrodes, designing and synthesizing high performance photoactive layer and low temperature processed electrode buffer layer materials, and device architecture engineering. To date, the highest power conversion efficiencies have reached over 10% of the flexible OSCs and 7.7% with average visible transmittance of 37% for the semitransparent OSCs. Here, a comprehensive overview of recent research progresses and perspectives on the related materials and devices of the flexible and semitransparent OSCs is provided.

Flexible and semitransparent organic solar cells (OSCs) are regarded as the most promising photovoltaic devices for the application of OSCs in wearable energy resources and building-integrated photovoltaics. Here, a comprehensive overview of recent research progresses and perspectives on the related materials and devices of the flexible and semitransparent OSCs is provided.