lizhendong

In organic solar cells, a major source of energy loss is attributed to nonradiative recombination from the interfacial charge transfer states to the ground state. By taking pentacene–C₆₀ complexes as model donor–acceptor systems, a comprehensive theoretical understanding of how molecular packing and charge delocalization impact these nonradiative recombination rates at donor–acceptor interfaces is provided.

The requirement of high-temperature calcination for titanium dioxide in (solid-state) dye-sensitized solar cells (DSSCs) implies challenges with respect to reduced energy consumption and the potential for flexible photovoltaic devices. Moreover, the use of dye molecules increases production costs and leads to problems related with dye bleaching. Therefore, fabrication of dye-free hybrid solar cells at low temperature is a promising alternative for current DSSC technology. In this work the authors fabricate hierarchically structured titania thin films by combining a polystyrene-block-polyethylene oxide template assisted sol–gel synthesis with nano-imprint lithography at low temperatures. The achieved films are filled with poly(3-hexylthiophene) to form the active layer of hybrid solar cells. The surface morphology is probed via scanning electron microscopy and atomic force microscopy, and the bulk film morphology is examined with grazing incidence X-ray scattering. Good light absorption by the active layer is proven by UV–vis spectroscopy. An enhancement in light absorption is observed and ascribed to light scattering in mesoporous titania films with imprinted superstructures. Accordingly a better photovoltaic performance is found for nano-imprinted solar cells at various angles of light incidence.

Nano-imprinted hybrid solar cells are fabricated at low temperature. Scanning electron microscopy, atomic force microscopy, and grazing incidence small-angle X-ray scattering offer morphological evidence that low temperature processed titania film could be imprinted by nano-imprint lithography retaining its nanostructures. UV–vis measurements verify the higher light absorption in nano-imprinted active layers. Consequently, nano-imprinted hybrid solar cells outperform unstructured devices.

Perovskite solar cells (PSCs) have been emerging as a breakthrough photovoltaic technology, holding unprecedented promise for low-cost, high-efficiency renewable electricity generation. However, potential toxicity associated with the state-of-the-art lead-containing PSCs has become a major concern. The past research in the development of lead-free PSCs has met with mixed success. Herein, the promise of coarse-grained B-γ-CsSnI₃ perovskite thin films as light absorber for efficient lead-free PSCs is demonstrated. Thermally-driven solid-state coarsening of B-γ-CsSnI₃ perovskite grains employed here is accompanied by an increase of tin-vacancy concentration in their crystal structure, as supported by first-principles calculations. The optimal device architecture for the efficient photovoltaic operation of these B-γ-CsSnI₃ thin films is identified through exploration of several device architectures. Via modulation of the B-γ-CsSnI₃ grain coarsening, together with the use of the optimal PSC architecture, planar heterojunction-depleted B-γ-CsSnI₃ PSCs with power conversion efficiency up to 3.31% are achieved without the use of any additives. The demonstrated strategies provide guidelines and prospects for developing future high-performance lead-free PVs.

The promise of coarse-grained B-γ-CsSnI₃ perovskite thin films as light absorber for efficient lead-free perovskite solar cells (PSCs) is demonstrated. Benefitting from thermally-driven solid-state coarsening of B-γ-CsSnI₃ perovskite grains and optimized device architecture, planar heterojunction-depleted B-γ-CsSnI₃ PSCs with power conversion efficiency up to 3.31% are achieved without the use of any additives.

A new low-band gap dyad DPP-Ful, which consists of covalently linked dithiafulvalene-functionalized diketopyrrolopyrrole as donor and fullerene (C₆₀) as the acceptor, has been designed and synthesized. Organic solar cells were successfully constructed using the DPP-Ful dyad as an active layer. This system has a record power-conversion efficiency (PCE) of 2.2 %, which is the highest value when compared to reported single-component organic solar cells.

Climbing alone: The combination of dithiafulvalene-functionalized diketopyrrolopyrrole (DPP) as donor with fullerene (Ful) as acceptor has been successfully explored. Its utilization in single-component organic solar cells (SC-OSCs) was investigated, and it was shown to have a record power-conversion efficiency. ITO=indium tin oxide.

In the present work, a Pb-assisted two step method is successfully proposed to fabricate high-quality CH₃NH₃Sn_0.5Pb_0.5I₃ (MASn_0.5Pb_0.5I₃) perovskite film on the indium tin oxide (ITO) glass/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) substrate. The film shows regular crystalline grains with a flat and compact morphology as well as full coverage on the planar PEDOT:PSS substrate. Remarkably, corresponding devices ITO/PEDOT:PSS/MASn_0.5Pb_0.5I₃/C₆₀/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline/Ag are fabricated with high reproducibility, achieving a high power conversion efficiency of 13.6%, which is, to the best of knowledge, the most efficient solar cell based on Sn-based perovskite.

A high efficiency inverted planar Sn-based perovskite solar cell is fabricated by utilizing a two-step solution processing technique. Through use of PbI₂ in combination with SnI₂, the Sn-based perovskite film quality is improved obviously. The lead contents are successfully reduced to 50% in the perovskite layer, and the power conversion efficiency of the best corresponding device reaches up to 13.6%.

A p-type oxide/2D hybrid van der Waals p–n heterojunction is demonstrated for the first time between SnO (tin monoxide) (the p-type oxide) and 2D MoS₂ (molybdenum disulfide), showing an ideality factor of 2 and rectification ratio up to 10⁴. The reported heterojunction is gate-tunable with typical anti-ambipolar transfer characteristics. Surface potential mapping is performed and a current model for such a heterojunction is proposed.

The electron-doping-induced phase transition of a prototypical perovskite SmNiO₃ induces a large and non-volatile optical refractive-index change and has great potential for active-photonic-device applications. Strong optical modulation from the visible to the mid-infrared is demonstrated using thin-film SmNiO₃. Modulation of a narrow band of light is demonstrated using plasmonic metasurfaces integrated with SmNiO₃.

Thinness-controlled perovskite wafers are directly prepared using a geometry-regulated dynamic-flow reaction system. It is found that the wafers are a superior material for photodetectors with a photocurrent response ≈350 times higher than that made of microcrystalline thin films. Moreover, the wafers are compatible with mass production of integrated circuits.

Efficient lead (Pb)-free inverted planar formamidinium tin triiodide (FASnI₃) perovskite solar cells (PVSCs) are demonstrated. Our FASnI₃ PVSCs achieved average power conversion efficiencies (PCEs) of 5.41% ± 0.46% and a maximum PCE of 6.22% under forward voltage scan. The PVSCs exhibit small photocurrent–voltage hysteresis and high reproducibility. The champion cell shows a steady-state efficiency of ≈6.00% for over 100 s.

A simple and versatile in situ fabrication of MAPbX₃ nanocrystal-embedded polymer composite films is developed by controlling the crystallization process from precursor solutions. The composite films exhibit enhanced photoluminescence properties, improved stability, and excellent piezoelectric and mechanical properties. Applications of these composite films as color converters in liquid-crystal-display backlights are demonstrated, showing bright potential in display technology.

In article 1600920, Aldo Di Carlo, Francesco Bonaccorso, and co-workers propose the use of solution-processed molybdenum disulfide (MoS₂) flakes in lead-halide perovskite solar cells. In this configuration, the MoS₂ flakes enhance the hole collection at the anode while protecting the perovskite from degradation. This has a remarkable effect on the lifetime stability of the cell, yielding power conversion efficiency, after 550 hours of endurance test, which is 33% higher compared to otherwise identical cells that do not exploit the MoS₂. An efficiency of 11.5% is also recorded in large area (>1 cm²) cells. This design might boost the commercialization of perovskite-based photovoltaics.

Doping of organic bulk heterojunction solar cells has the potential to improve their power conversion efficiency (PCE). Deconvoluting the effect of doping on charge transport, recombination, and energetic disorder remains challenging. It is demonstrated that molecular doping has two competing effects: on one hand, dopant ions create additional traps while on the other hand free dopant-induced charges fill deep states possibly leading to V _OC and mobility increases. It is shown that molar dopant concentrations as low as a few parts per million can improve the PCE of organic bulk heterojunctions. Higher concentrations degrade the performance of the cells. In doped cells where PCE is observed to increase, such improvement cannot be attributed to better charge transport. Instead, the V _OC increase in unannealed P3HT:PCBM cells upon doping is indeed due to trap filling, while for annealed P3HT:PCBM cells the change in V _OC is related to morphology changes and dopant segregation. In PCDTBT:PC70BM cells, the enhanced PCE upon doping is explained by changes in the thickness of the active layer. This study highlights the complexity of bulk doping in organic solar cells due to the generally low doping efficiency and the constraint on doping concentrations to avoid carrier recombination and adverse morphology changes.

Ultralow level doping (≈ppm) can increase the power conversion efficiency of organic solar cells. Trap states filling by free charges and trap creation by dopant ions have competing effects on carrier mobility and open circuit voltage thereby imposing constraints on the effectiveness of doping. Measurements are performed to study what electronic process dominates in different materials or fabrication conditions.

Bimolecular recombination in bulk heterojunction organic solar cells is the process by which nongeminate photogenerated free carriers encounter each other, and combine to form a charge transfer (CT) state which subsequently relaxes to the ground state. It is governed by the diffusion of the slower and faster carriers toward the electron donor–acceptor interface. In an increasing number of systems, the recombination rate constant is measured to be lower than that predicted by Langevin's model for relative Brownian motion and the capture of opposite charges. This study investigates the dynamics of charge generation, transport, and recombination in a nematic liquid crystalline donor:fullerene acceptor system that gives solar cells with initial power conversion efficiencies of >9.5%. Unusually, and advantageously from a manufacturing perspective, these efficiencies are maintained in junctions thicker than 300 nm. Despite finding imbalanced and moderate carrier mobilities in this blend, strongly suppressed bimolecular recombination is observed, which is ≈150 times less than predicted by Langevin theory, or indeed, more recent and advanced models that take into account the domain size and the spatial separation of electrons and holes. The suppressed bimolecular recombination arises from the fact that ground-state decay of the CT state is significantly slower than dissociation.

A detailed study of bimolecular recombination in a high efficiency organic solar cell, comprised of a liquid crystalline donor and PC71BM, is presented. Using multiple techniques, it is shown that the bimolecular recombination is nearly 150 times suppressed with respect to that predicted by Langevin theory. This reduction is attributed to an equilibrium between charge transfer states and free charges.