Ligang Yuan

Recently, all-inorganic cesium lead halide (CsPbX₃, X = Cl, Br, I) perovskite nanocrystals have drawn much attention because of their outstanding photophysical properties and potential applications. In this work, a simple and efficient solvothermal approach to prepare CsPbX₃ nanocrystals with tunable and bright photoluminescent (PL) properties, controllable composition, and morphology is presented. CsPbX₃ nanocubes are successfully prepared with bright emission high PL quantum yield up to 80% covering the full visible range and narrow emission line widths (from 12 to 36 nm). More importantly, ultrathin CsPbX₃ (X = Cl/Br, Br, and Br/I) nanowires (with diameter as small as ≈2.6 nm) can be prepared in a very high morphological yield (almost 100%). A strong quantum confinement effect is observed in the ultrathin nanowires, in which both the absorption and emission peaks shift to shorter wavelength range compared to their bulk bandgap. The reaction parameters, such as temperature and precursors, are varied to investigate the growth process. A white light-emitting device prototype device with wide color gamut covering up to 120% of the National Television System Committee standard has been demonstrated by using CsPbBr₃ nanocrystals as the green light source. The method in this study provides a simple and efficient way to prepare high-quality CsPbX₃ nanocrystals.

A solvothermal method is developed to prepare high-quality all-inorganic cesium lead halide (CsPbX₃) nanocrystals. Monodisperse CsPbX₃ nanocubes and ultrathin CsPbX₃ nanowires are prepared. By using the prepared CsPbBr₃ nanocrystals as the green light source, a white light-emitting prototype device with wide color gamut covering up to 120% of the National Television System Committee standard is fabricated.

Organic–inorganic perovskites with intriguing optical and electrical properties have attracted significant research interests due to their excellent performance in optoelectronic devices. Recent efforts on preparing uniform and large-grain polycrystalline perovskite films have led to enhanced carrier lifetime up to several microseconds. However, the mobility and trap densities of polycrystalline perovskite films are still significantly behind their single-crystal counterparts. Here, a facile topotactic-oriented attachment (TOA) process to grow highly oriented perovskite films, featuring strong uniaxial-crystallographic texture, micrometer-grain morphology, high crystallinity, low trap density (≈4 × 10¹⁴ cm⁻³), and unprecedented 9 GHz charge-carrier mobility (71 cm² V⁻¹ s⁻¹), is demonstrated. TOA-perovskite-based n-i-p planar solar cells show minimal discrepancies between stabilized efficiency (19.0%) and reverse-scan efficiency (19.7%). The TOA process is also applicable for growing other state-of-the-art perovskite alloys, including triple-cation and mixed-halide perovskites.

A facile topotactic-oriented attachment process can produce uniaxially oriented perovskite thin films with micrometer-grain morphology, high crystallinity, low trap density (≈4 × 10¹⁴ cm⁻³), and fast 9 GHz charge-carrier mobility (71 cm² V⁻¹ s⁻¹). The n-i-p planar perovskite solar cell exhibits a power conversion efficiency of 19.7% (with stabilized efficiency output of 19.0%).

Minimization of defects in absorber materials is essential for hybrid perovskite solar cells, especially when constructing thick polycrystalline layers in a planar configuration. Here, a simple methylamine solution-based additive is reported to improve film quality with nearly an order of magnitude reduction in intrinsic defect concentration. In the resultant film, an increase in carrier lifetime as a result of a decrease in shallow electronic disorder is observed. This superior crystalline film quality is further evidenced via a doubled spin relaxation time as compared with other reports. Bearing sufficient carrier diffusion length, a thick absorber layer (≈650 nm) is implemented in planar devices to achieve a champion power conversion efficiency of 20.02% with a stabilized output efficiency of 19.01% under one sun illumination. This work demonstrates a simple approach to improve hybrid perovskite film quality by substantial reduction of intrinsic defects for wide applications in optoelectronics.

A simple methylamine solution-based additive to improve film quality with nearly an order of magnitude reduction in the concentration of intrinsic defects is reported, and the relevant perovskite solar cells achieve a champion power conversion efficiency of 20.02% with a stabilized output efficiency of 19.01% under 1 sun illumination.

Intrinsically stretchable light-emitting diodes (LEDs) are demonstrated using organometal-halide-perovskite/polymer composite emitters. The polymer matrix serves as a microscale elastic connector for the rigid and brittle perovskite and induces stretchability to the composite emissive layers. The stretchable LEDs consist of poly(ethylene oxide)-modified poly(3,4-ethylenedioxythiophene) polystyrene sulfonate as a transparent and stretchable anode, a perovskite/polymer composite emissive layer, and eutectic indium–gallium as the cathode. The devices exhibit a turn-on voltage of 2.4 V, and a maximum luminance intensity of 15 960 cd m⁻² at 8.5 V. Such performance far exceeds all reported intrinsically stretchable LEDs based on electroluminescent polymers. The stretchable perovskite LEDs are mechanically robust and can be reversibly stretched up to 40% strain for 100 cycles without failure.

Intrinsically stretchable light-emitting diodes (LEDs) are demonstrated using organometal-halide-perovskite/polymer composite emitters. The polymer matrix serves as a microscale elastic connector for the rigid and brittle perovskite and induces stretchability to the composite emissive layers. Such an approach results in bright and stretchable perovskite LEDs that can be reversibly stretched up to 40% uniaxial strain for 100 cycles.

Perovskite solar cells (PSCs) and organic solar cells (OSCs) are promising renewable light-harvesting technologies with high performance, but the utilization of hazardous dopants and high boiling additives is harmful to all forms of life and the environment. Herein, new multirole π-conjugated polymers (P1–P3) are developed via a rational design approach through theoretical hindsight, further successfully subjecting them into dopant-free PSCs as hole-transporting materials and additive-free OSCs as photoactive donors, respectively. Especially, P3-based PSCs and OSCs not only show high power conversion efficiencies of 17.28% and 8.26%, but also display an excellent ambient stability up to 30 d (for PSCs only), owing to their inherent superior optoelectronic properties in their pristine form. Overall, the rational approach promises to support the development of environmentally and economically sustainable PSCs and OSCs.

New multirole π-conjugated polymers are developed via a rational design approach through theoretical hindsight, further successfully subjecting them into dopant-free perovskite solar cells as hole-transporting materials with high power conversion efficiency (PCE) of 17.28%, and additive-free organic solar cells as photoactive donors with high PCE of 8.26%.

Tin (Sn)-based perovskites are increasingly attractive because they offer lead-free alternatives in perovskite solar cells. However, depositing high-quality Sn-based perovskite films is still a challenge, particularly for low-temperature planar heterojunction (PHJ) devices. Here, a “multichannel interdiffusion” protocol is demonstrated by annealing stacked layers of aqueous solution deposited formamidinium iodide (FAI)/polymer layer followed with an evaporated SnI₂ layer to create uniform FASnI₃ films. In this protocol, tiny FAI crystals, significantly inhibited by the introduced polymer, can offer multiple interdiffusion pathways for complete reaction with SnI₂. What is more, water, rather than traditional aprotic organic solvents, is used to dissolve the precursors. The best-performing FASnI₃ PHJ solar cell assembled by this protocol exhibits a power conversion efficiency (PCE) of 3.98%. In addition, a flexible FASnI₃-based flexible solar cell assembled on a polyethylene naphthalate–indium tin oxide flexible substrate with a PCE of 3.12% is demonstrated. This novel interdiffusion process can help to further boost the performance of lead-free Sn-based perovskites.

Flexible lead-free perovskite solar cells are achieved using FASnI₃ via a novel water-based multichannel interdiffusion protocol for the first time. Nanosized formamidinium iodide crystals inhibited by the introduced polymer of the aqueous salt/polymer solutions provide multiple channels to completely react with evaporated SnI₂. The highest power conversion efficiency of 3.98% and 3.12% is realized for rigid and flexible substrate, respectively.

Large-scale fabrication of organic solar cells requires an active layer with high thickness tolerability and the use of environment-friendly solvents. Thick films with high-performance can be achieved via a ternary strategy studied herein. The ternary system consists of one polymer donor, one small molecule donor, and one fullerene acceptor. The small molecule enhances the crystallinity and face-on orientation of the active layer, leading to improved thickness tolerability compared with that of a polymer-fullerene binary system. An active layer with 270 nm thickness exhibits an average power conversion efficiency (PCE) of 10.78%, while the PCE is less than 8% with such thick film for binary system. Furthermore, large-area devices are successfully fabricated using polyethylene terephthalate (PET)/Silver gride or indium tin oxide (ITO)-based transparent flexible substrates. The product shows a high PCE of 8.28% with an area of 1.25 cm² for a single cell and 5.18% for a 20 cm² module. This study demonstrates that ternary organic solar cells exhibit great potential for large-scale fabrication and future applications.

To achieve commercialization of organic solar cells, high thickness tolerability must be obtained and chlorinated solvents must be replaced. This study demonstrates an active layer with 270 nm thickness exhibits a power conversion efficiency of 10.78% using o-xylene as processing solvent. Large-area devices are successfully fabricated using polyethylene terephthalate-based transparent flexible substrate.

The power conversion efficiency of colloidal PbS-quantum-dot (QD)-based solar cells is significantly hampered by lower-than-expected open circuit voltage (V_OC). The V_OC deficit is considerably higher in QD-based solar cells compared to other types of existing solar cells due to in-gap trap-induced bulk recombination of photogenerated carriers. Here, this study reports a ligand exchange procedure based on a mixture of zinc iodide and 3-mercaptopropyonic acid to reduce the V_OC deficit without compromising the high current density. This layer-by-layer solid state ligand exchange treatment enhances the photovoltaic performance from 6.62 to 9.92% with a significant improvement in V_OC from 0.58 to 0.66 V. This study further employs optoelectronic characterization, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy to understand the origin of V_OC improvement. The mixed-ligand treatment reduces the sub-bandgap traps and significantly reduces bulk recombination in the devices.

A mixed-ligand treatment for the fabrication of lead sulphide colloidal quantum dot solar cells is demonstrated. The mixed-ligand treatment facilitates the advantages of both organic (3-mercaptopropionic acid) and inorganic (zinc iodide) ligands to improve charge transport and trap passivation leading to a power conversion efficiency of 9.92% at a V_OC of 0.66 V.

Interfacial engineering of perovskite solar cells (PSCs) is attracting intensive attention owing to the charge transfer efficiency at an interface, which greatly influences the photovoltaic performance. This study demonstrates the modification of a TiO₂ electron-transporting layer with various amino acids, which affects charge transfer efficiency at the TiO₂/CH₃NH₃PbI₃ interface in PSC, among which the l-alanine-modified cell exhibits the best power conversion efficiency with 30% enhancement. This study also shows that the (110) plane of perovskite crystallites tends to align in the direction perpendicular to the amino-acid-modified TiO₂ as observed in grazing-incidence wide-angle X-ray scattering of thin CH₃NH₃PbI₃ perovskite film. Electrochemical impedance spectroscopy reveals less charge transfer resistance at the TiO₂/CH₃NH₃PbI₃ interface after being modified with amino acids, which is also supported by the lower intensity of steady-state photoluminescence (PL) and the reduced PL lifetime of perovskite. In addition, based on the PL measurement with excitation from different side of the sample, amino-acid-modified samples show less surface trapping effect compared to the sample without modification, which may also facilitate charge transfer efficiency at the interface. The results suggest that appropriate orientation of perovskite crystallites at the interface and trap-passivation are the niche for better photovoltaic performance.

The (110) plane of CH₃NH₃PbI₃ crystallites adjacent to the amino-acid-modified TiO₂ surface tends to align in the direciton perpendicular to the TiO₂ surface. Such crystalline orientation significantly enhances charge transfer efficiency at the TiO₂/CH₃NH₃PbI₃ interface and greatly improves the photovotaic performance of perovskite solar cells.