wangzhaowei

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 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%.

The rapid rise in power conversion efficiencies of lead-based perovskite solar cells (PSCs) has established their promise, motivating scale-up and commercialization. As a thin film solar cell, interfacial properties are key to the performance of PSCs; there is a need to further understand which properties are critical to control. In this work, the impact of the compact TiO₂ (com-TiO₂) film properties on the performance of mesoporous PSCs is studied. Com-TiO₂ layers are fabricated by spray pyrolysis as well as by atomic layer deposition (ALD), using ALD as a proof-of-concept method to achieve highly conformal films of precisely controlled thickness. The com-TiO₂ layers' conformality and surface roughness are examined by microscopy techniques; their relative crystallinity is studied by grazing-incidence X-ray diffraction with a synchrotron source and an in situ annealing chamber; and completed devices are analyzed by J–V and impedance spectroscopy techniques. The results show that an ultraconformal com-TiO₂ layer can be thinned to 4 nm and match the performance of a ≈50 nm spray-pyrolysis TiO₂ layer. This work concludes that film conformality is the primary consideration for creating a high-performing com-TiO₂ layer, overriding any effects of film crystallinity—a finding that can guide fabrication choices for the scale-up of PSCs.

Highly conformal ≈4 nm compact TiO₂ layers by atomic layer deposition are demonstrated to match the performance of ≈50 nm spray-pyrolysis TiO₂ layers in mesoporous perovskite solar cells. TiO₂ films are characterized by grazing-incidence X-ray diffraction using a synchrotron source. Film thickness and conformality are found to be more critical to a high-performing compact TiO₂ layer than the degree of crystallinity.

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.

A low-bandgap (1.33 eV) Sn-based MA_0.5FA_0.5Pb_0.75Sn_0.25I₃ perovskite is developed via combined compositional, process, and interfacial engineering. It can deliver a high power conversion efficiency (PCE) of 14.19%. Finally, a four-terminal all-perovskite tandem solar cell is demonstrated by combining this low-bandgap cell with a semitransparent MAPbI₃ cell to achieve a high efficiency of 19.08%.

In this work, the detailed morphology studies of polymer poly(3-hexylthiophene-2,5-diyl) (P3HT):fullerene(PCBM) and polymer(P3HT):polymer naphthalene diimide thiophene (PNDIT) solar cell are presented to understand the challenge for getting high performance all-polymer solar cells. The in situ X-ray scattering and optical interferometry and ex situ hard and soft X-ray scattering and imaging techniques are used to characterize the bulk heterojunction (BHJ) ink during drying and in dried state. The crystallization of P3HT polymers in P3HT:PCBM bulk heterojunction shows very different behavior compared to that of P3HT:PNDIT BHJ due to different mobilities of P3HT in the donor:acceptor glass. Supplemented by the ex situ grazing incidence X-ray diffraction and soft X-ray scattering, PNDIT has a lower tendency to form a mixed phase with P3HT than PCBM, which may be the key to inhibit the donor polymer crystallization process, thus creating preferred small phase separation between the donor and acceptor polymer.

The morphology development of polymer:fullerene and polymer:polymer solar cells is characterized by real-time X-ray scattering and interferometry. Polymer:fullerence blends show a smaller phase-separation due to high glass-transition temperature of PCBM acceptors, compared to polymer:polymer blends.