wangzhaowei

Using a “multifluorination” strategy, ambipolar donor–acceptor conjugated polymer with hole and electron mobility (μ_h and μ_e) up to 3.94 and 3.50 cm² V⁻¹ s⁻¹, respectively, and unipolar n-type donor–acceptor conjugated polymers with μ_e up to 4.97 cm² V⁻¹ s⁻¹ is synthesized with isoindigo as acceptor units.

Despite the breakthrough of over 22% power conversion efficiency demonstrated in organic–inorganic hybrid perovskite solar cells (PVSCs), critical concerns pertaining to the instability and toxicity still remain that may potentially hinder their commercialization. In this study, a new chemical approach using environmentally friendly strontium chloride (SrCl₂) as a precursor for perovskite preparation is demonstrated to result in enhanced device performance and stability of the derived hole-conductor-free printable mesoscopic PVSCs. The CH₃NH₃PbI₃ perovskite is chemically modified by introducing SrCl₂ in the precursor solution. The results from structural, elemental, and morphological analyses show that the incorporation of SrCl₂ affords the formation of CH₃NH₃PbI₃(SrCl₂)_x perovskites endowed with lower defect concentration and better pore filling in the derived mesoscopic PVSCs. The optimized compositional CH₃NH₃PbI₃(SrCl₂)_0.1 perovskite can substantially enhance the photovoltaic performance of the derived hole-conductor-free device to 15.9%, outperforming the value (13.0%) of the pristine CH₃NH₃PbI₃ device. More importantly, the stability of the device in ambient air under illumination is also improved.

A new compositional perovskite, CH₃NH₃PbI₃(SrCl₂)_0.1 with more compact morphology and lower defect concentration is presented. Consequently, a power conversion efficiency of 15.9% with enhanced stability is achieved by employing the structure of hole-conductor-free fully printable mesoscopic perovskite solar cell.

A room-temperature perovskite material yielding a power conversion efficiency of 18.1% (stabilized at 17.7%) is demonstrated by judicious selection of cations. Both cesium and methylammonium are necessary for room-temperature formamidinium-based perovskite to obtain the photoactive crystalline perovskite phase and high-quality crystals. This room-temperature-made perovskite material shows great potential for low-cost, large-scale manufacturing such as roll-to-roll processing.

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.

A polydimethylsiloxane cylindrical-hole-template-confined solution-growth method is developed to fabricate densely packed CsPbCl_{3− x} Br _x microdisk laser arrays. Furthermore, a strategy to integrate multicolored microdisk laser (MDL) arrays is demonstrated that simultaneously lase in the deep blue, blue, cyan, and green by means of gas-phase replacement of Cl by Br from initial CsPbCl₃ MDLs in HBr vapor.

A new, all room-temperature solution process is developed to fabricate efficient, low-cost, and stable perovskite solar cells (PVSCs). The PVSCs show high efficiency of 17.10% and 14.19%, with no hysteresis on rigid and flexible substrates, respectively, which are the best efficiencies reported to date for PVSCs fabricated by room-temperature solution-processed techniques. The flexible PVSCs show a remarkable power-per-weight of 23.26 W g⁻¹.

The morphology, photophysics, and device performance of solar cells based on the low bandgap polymer poly[[2,6′-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene]3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl (PBDTTT-EFT) (also known as PTB7-Th) blended with different fullerene acceptors: Phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM), phenyl-C₇₁ -butyric acid methyl ester (PC₇₁BM), or indene-C₆₀ bisadduct (ICBA) are correlated. Compared to PC₇₁ BM-based cells – which achieve a power conversion efficiency (PCE) of 9.4% – cells using ICBA achieve a higher open-circuit voltage (V_OC) of 1.0 V albeit with a lower PCE of 7.1%. To understand the origin of this lower PCE, the morphology and photophysics have been thoroughly characterized. Hard and soft X-ray scattering measurements reveal that the PBDTTT-EFT:ICBA blend has a lower crystallinity, lower domain purity, and smaller domain size compared to the PBDTTT-EFT:PC₇₁BM blend. Incomplete photoluminescence quenching is also found in the ICBA blend with transient absorption measurements showing faster recombination dynamics at short timescales. Transient photovoltage measurements highlight further differences in recombination at longer timeframes due to the more intermixed morphology of the ICBA blend. Interestingly, a mild thermal treatment improves the performance of PBDTTT-EFT:ICBA cells which is exploited in the fabrication of a homo PBDTTT-EFT:ICBA tandem solar cell with PCE of 9.0% and V_OC of 1.93 V.

The mixing behavior of a high-efficiency polymer with various fullerene derivatives is investigated. Compared to solar cells using either PC₆₁BM or PC₇₁ BM as acceptor, cells using ICBA have a lower efficiency due to a more intermixed morphology. ICBA blends, however, show a higher thermal stability which is exploited in the fabrication of homo-tandem cells with 9.0% power conversion efficiency.

Perovskite materials due to their exceptional photophysical properties are beginning to dominate the field of thin-film optoelectronic devices. However, one of the primary challenges is the processing-dependent variability in the properties, thus making it imperative to understand the origin of such variations. Here, it is discovered that the precursor solution aging time before it is cast into a thin film, is a subtle but a very important factor that dramatically affects the overall thin-film formation and crystallinity and therein factors such as grain growth, phase purity, surface uniformity, trap state density, and overall solar cell performance. It is shown that progressive aging of the precursor promotes efficient formation of larger seeds after the fast nucleation of a large density of small seeds. The hot-casting method then leads to the growth of large grains in uniform thin-films with excellent crystallinity validated using scanning microscopy images and X-ray diffraction patterns. The high-quality films cast from aged solution is ideal for thin-film photovoltaic device fabrication with reduced shunt current and good charge transport. This observation is a significant step toward achieving highly crystalline thin-films with reliability in device performance and establishes the subtle but dramatic effect of solution aging before fabricating perovskite thin-films.

A direct correlation between precursor aging time and crystalline quality of hybrid perovskite-based thin films is discovered and systematically elucidated. Progressive aging of precursor results in a pinhole-free thin film with optimal phase purity that results in high-efficiency planar solar cells.

Deliberate halide exchange between unstable intermediate HPbI₂Br and nonstoichiometric FAI is employed to produce high-quality FAPbI_3–xBr_x (x ≈ 0.44), which eliminates the use of antisolvent dripping and other post-treatment techniques. The obtained perovskite thin film demonstrates high crystallinity and a large and compact crystal domain up to 2–3 µm. The corresponding device shows power conversion efficiency of up to around 19.0%, with reliable stability and reproducibility.

Metal halide perovskites, a class of crystalline semiconductors with unique optical and electronic properties, are emerging as potential solutions for low-cost photovoltaics and photonic sources in fields of solar cells, sensors, light-emitting diodes and lasers. Regardless of significant progress on device efficiency with the control over perovskite structures and film morphologies, unveiling the interface energetics and band alignment of these perovskite systems is indispensable for the performance optimization in the optoelectronic applications by grasping the photon harvest and charge transport processes. Herein we review the recent advances in the energetics of metal halide perovskite interfaces. The electronic properties of perovskite materials are addressed in terms of halide substitution, thermal annealing and substrate effects as well as trap states. The energy level alignments of interfaces between perovskite films and charge transport layers are then discussed, which is correlated to the photovoltaic properties in perovskite solar cells.

Recent advances in energetics in metal halide perovskite interfaces are reviewed with a combined discussion of electronic structures of metal halide perovskites and energy level alignment at perovskite/organic heterointerfaces through photoemission spectroscopy techniques. The energetics at the perovskite interfaces with various carrier transport materials is highlighted, suggesting the impact on photocurrent generation process in perovskite solar cells.

Organometallic perovskites, solution-processable materials with outstanding optoelectronic properties and high index of refraction, provide a platform for all-dielectric metamaterials operating at visible frequencies. Perovskite metasurfaces with structural coloring tunable across visible frequencies are realized through subwavelength structuring. Moreover, a threefold increase of the luminescence yield and comparable reduction of luminescence decay time are observed.