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A tandem structure was invented to enhance photon utilization efficiency and reduce thermal loss. Considering the unique advantages of non-fullerene acceptors (NFAs), the combination of NFAs and the tandem concept shows great potential for organic photovoltaics (OPVs). Herein, a simple strategy to balance the voltage-current trade-off in tandem OPVs by employing mixed NFAs in rear sub-cells is reported. The V OC and J SC of rear sub-cells can be tuned by using the blend of donor/NFA/NFA. This strategy offers an easy approach to balance the V OC and J SC in tandem OPVs toward higher power conversion efficiency (PCE) without rational and careful synthesis of new materials. Tandem OPVs based on mixed NFAs in rear sub-cells exhibited the best PCE of 13.3% in the lab. Importantly, the tandem devices were certified by the National Renewable Energy Laboratory (NREL) under asymptotic scans, and a PCE of 11.52% was achieved and recognized on the most recent NREL chart. Organic photovoltaics (OPVs) have attracted considerable attention in the last decade due to some potential advantages, such as flexibility, light weight, possible semi-transparency, and fast large-area fabrication with low energy consumption. To achieve higher performing OPVs, a tandem structure was invented by stacking two or more sub-cells together. In tandem OPVs, the photon utilization efficiency can be improved and the thermal losses can be reduced. Herein, a simple strategy to balance the voltage-current trade-off in tandem OPVs by employing mixed non-fullerene acceptors in rear sub-cells is reported. By this strategy, tandem OPVs exhibited the best power conversion efficiency (PCE) of 13.3% in the lab. Importantly, the tandem devices were certified by the National Renewable Energy Laboratory (NREL) under the new protocols (asymptotic scans), and a PCE of 11.52% was achieved and recognized on the most recent NREL chart. A simple strategy to balance the voltage-current trade-off in tandem organic photovoltaics by employing mixed non-fullerene acceptors in rear sub-cells is reported. The tandem device with the best power conversion efficiency (PCE) of 13.3% was achieved in the lab. Importantly, the tandem devices were certified by the National Renewable Energy Laboratory (NREL) under the new protocols (asymptotic scans, which are much tougher than regular fast scans); a PCE of 11.52% was achieved and recognized on the most recent NREL chart.

Anharmonic crystal lattice dynamics have been observed in lead halide perovskites on picosecond timescales. Here, we report that the soft nature of the perovskite crystal lattice gives rise to dynamic fluctuations in the electronic properties of excited states. We use linear polarization selective transient absorption spectroscopy to study the charge carrier relaxation dynamics in lead-halide perovskite films and nanocrystals. We find that photo-excited charge carriers maintain an initial polarization anisotropy for several picoseconds, independent of crystallite size and composition, and well beyond the reported timescales of carrier scattering. First-principles calculations find intrinsic anisotropies in the transition dipole moment, which depend on the orientation of light polarization and the polar distortion of the local crystal lattice. Lattice dynamics are imprinted in the optical transitions and anisotropies arise on the time-scales of structural motion. The strong coupling between electronic states and structural dynamics requires a unique interpretation of recombination and transport mechanisms.

Decreasing perovskite nanocrystal size increases radiative recombination due to the quantum confinement effect, but also increases the Auger recombination rate which leads to carrier imbalance in the emitting layers of electroluminescent devices. Here, we overcome this trade‐off by increasing the exciton effective mass without affecting the size, which is realized through the trace Cd2+ doping of formamidinium lead bromide perovskite nanocrystals. We observe an ~2.7 times increase in the exciton binding energy benefiting from a slight distortion of the [BX6]4− octahedra caused by doping in the case of that the Auger recombination rate is almost unchanged. As a result, bright color‐saturated green emitting perovskite nanocrystals with a photoluminescence quantum yield of 96 % are obtained. Cd2+ doping also shifts up the energy levels of the nanocrystals, relative to the Fermi level so that heavily n‐doped emitters convert into only slightly n‐doped ones; this boosts the charge injection efficiency of the corresponding light‐emitting diodes. The light‐emitting devices based on those nanocrystals reached a high external quantum efficiency of 29.4 % corresponding to a current efficiency of 123 cd A−1, and showed dramatically improved device lifetime, with a narrow bandwidth of 22 nm and Commission Internationale de I'Eclairage coordinates of (0.20, 0.76) for color‐saturated green emission for the electroluminescence peak centered at 534 nm, thus being fully compliant with the latest standard for wide color gamut displays. [ABSTRACT FROM AUTHOR]

Direct current (DC) from mechanical energy built on the tribovoltaic effect is promising for the development of self‐powered flexible electronics. A semiconductor triboelectric generator is one of the optimized solutions for DC output. However, it remains underutilized because of its low output power and insufficient insight into the fundamental principles of charge generation and transport at dynamic interfaces. Herein, a flexible fabric‐based DC generator that relies on a metal–semiconducting polymer interface constructed by an asymmetric Schottky junction between a poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS)‐coated fabric and an aluminum (Al) foil is reported. The dependence of the electrical output performance of the device on the doping carrier concentration using different types of PEDOT:PSS to modulate the Schottky barrier height, validating both the work function and conductivity of the triboelectric material, which plays a fundamental role in DC generation, is explored. A large work function difference is required to create a high built‐in electric field for efficient separation of electron–hole pairs. Decent conductivity also fulfills an integral role in the innate carrier‐transport capability. Accordingly, an open‐circuit voltage (Voc) of 800 mV, a short‐circuit current (Isc) of 80 μA, and a power density of 6.7 mW cm−2 are yielded simultaneously. [ABSTRACT FROM AUTHOR]

Photo‐mediated synthesis wielding localized surface plasmon resonance (LSPR) of nanoscale metal is widely applied to sculpt silver (Ag) nanocrystals with controllable dimensions and morphologies. However, this photo‐mediated strategy remains underutilized owing to low efficiency and inferior quality in conventional batch reactors. Here, the effective synthesis of Ag nanocrystals is demonstrated via flow reactors and elucidates the photo‐mediated anisotropic growth mechanism. The investigation reveals that the intersection between excitation wavelengths and LSPR of Ag nanocrystals is a prerequisite for their growth. The final morphology is highly correlated with excitation wavelengths, which modulate the redox potential (reaction barrier) of Ag nanocrystals featuring distinct defective structures. Thus, by utilizing tandem‐connected flow reactors, size‐controllable Ag nanoplates can be yielded in a highly efficient cascade growth manner. In addition, composite conductive ink (submicron/nano‐Ag particles) is employed to create high‐performance flexible transparent electrodes. A sixfold conductivity enhancement especially under low sintering temperature (<80 °C), along with superior transmittance (over 90%), and distinguished cyclic durability (negligible resistance change over 1000 cycles) are achieved simultaneously. The study not only establishes comprehensive insights into the acquisition of well‐defined Ag nanocrystals in flow reactors but also ushers in enormous feasibility toward high‐performance and cost‐effective flexible electronics. [ABSTRACT FROM AUTHOR]

Decreasing the power consumption of light‐emitting diodes (LEDs) and increasing the energy generation of solar cells are crucial tasks toward the mitigation of greenhouse gas emissions and Paris Agreement goals. Lead (Pb)‐free halide double perovskites, identified as environmentally friendly alternatives to Pb‐based perovskites, are not deemed useful thus far due to the absence of high photoluminescence quantum yield (PLQY) examples and large bandgaps. Herein, penta‐cationic antimony (Sb5+)‐doping strategy is demonstrated for the benchmark material of Cs2NaInCl6, achieving blue emission with near‐unity PLQY and the lowest bandgap of 1.24 eV. The excellent PLQY observed in the material is attributed to Sb5+ doping‐induced Jahn–Teller distortion in Cs2NaInCl6 and a newly emerged band structure, which has remained undisclosed in all previous reports. This groundbreaking discovery represents the first instance in the field of perovskite materials where the incorporation of a single dopant has resulted in a zero‐to‐one enhancement in their emission profile. This breakthrough is expected to have profound implications for advancing research in the utilization of similar dopants, such as manganese cations (Mn6+ and Mn7+), not only in halide perovskite structures but also in oxide‐based perovskites and other semiconductor systems. [ABSTRACT FROM AUTHOR]

Wide‐bandgap metal compound‐based dopant‐free passivating contacts have been explored to fabricate crystalline silicon (Si) solar cells to mitigate the high carrier recombination rate of metal‐Si contact directly. Here, an over 4‐nm‐thick single‐layer strontium fluoride (SrFx) and a double‐layer SrFx/lithium fluoride (LiF) films deposited by a facile vacuum thermal evaporation are developed to act as high‐performance electron‐selective contacts. SrFx with ultra‐low work function (2.8 eV) induces a strong downward band bending at the n‐type Si (n‐Si)/SrFx interface, and a dipole active layer exists at the SrFx/aluminum (Al) interface, enabling a low contact resistivity (ρc) of 34.1 mΩ cm2 and thus yielding an impressive fill factor (FF) of 82.8%. Eventually, a power conversion efficiency (PCE) of 20.1% is achieved in the SrFx‐based solar cell. Moreover, in the n‐Si/SrFx/LiF/Al contact, the diffusion of Li in the SrFx film favors facilitating electron transport as well as relaxing its thickness restriction, inhibiting carrier recombination. And an impressive FF of 83.7% with a low ρc of 25.9 mΩ cm2, an improved open‐circuit voltage of 631 mV, and a short‐circuit current density of 39.9 mA/cm2 are attained, resulting in a champion PCE of 21.1%. Double‐layer SrFx/LiF deposited by a simple process provides a grand opportunity to fabricate low‐cost and high‐PCE photovoltaic devices. [ABSTRACT FROM AUTHOR]