Explore the vast range of titles available.

The conversion efficiency of solar energy in semiconductors is fundamentally limited by ultrafast hot-carrier relaxation processes, and slowing down these processes is critical for improved energy harvesting. Here we report formamidinium tin iodide (FASnI3) nanocrystals where quantum confinement effects yield an evolution from a continuous band structure to separate energy states with decreasing nanocrystal size, as observed by transient absorption spectroscopy. The appearance of separate energy levels slows down the relaxation of hot carriers by two orders of magnitude at low injected carrier densities (<1 carrier pair per nanoparticle). The observed build up time of the ground-state bleach at the band edge is two orders of magnitude slower in FASnI3 nanocrystals than in lead halide perovskite bulk and nanocrystals, which we attribute to a phonon bottleneck effect. Our results highlight the promise of lead-free perovskite nanocrystals for high-efficiency photovoltaic applications operating above the Shockley–Queisser limit.Tin-based perovskite nanocrystals with slower than usual relaxation dynamics holds promise for superior lead-free perovskite optoelectronic devices.

Understanding and control of ultrafast non-equilibrium processes in semiconductors is key to making use of the full photon energy before relaxation, leading to new ways to break efficiency limits for solar energy conversion. In this work, we demonstrate the observation and modulation of slow relaxation in uniformly mixed tin-lead perovskites (MASn x Pb 1-x I 3 and CsSn x Pb 1-x I 3 nanocrystals). Transient absorption measurements reveal that slow cooling mediated by a hot phonon bottleneck effect appears at carrier densities above ~10 18  cm −3 for tin-lead alloy nanocrystals, and tin addition is found to give rise to suppressed cooling. Within the alloy nanoparticles, the combination of a newly introduced high-energy band, screened Fröhlich interaction, suppressed Klemens decay and reduced thermal conductivity (acoustic phonon transport) with increased tin content contributes to the slowed relaxation. For inorganic nanocrystals where defect states couple strongly with carriers, sodium doping has been confirmed to benefit in maintaining hot carriers by decoupling them from deep defects, leading to a decreased energy-loss rate during thermalization and an enhanced hot phonon bottleneck effect. The slow cooling we observe uncovers the intrinsic photophysics of perovskite nanocrystals, with implications for photovoltaic applications where suppressed cooling could lead to hot-carrier solar cells.

Solar fuels offer a promising approach to provide sustainable fuels by harnessing sunlight 1 , 2 . Following a decade of advancement, Cu 2 O photocathodes are capable of delivering a performance comparable to that of photoelectrodes with established photovoltaic materials 3 , 4 – 5 . However, considerable bulk charge carrier recombination that is poorly understood still limits further advances in performance 6 . Here we demonstrate performance of Cu 2 O photocathodes beyond the state-of-the-art by exploiting a new conceptual understanding of carrier recombination and transport in single-crystal Cu 2 O thin films. Using ambient liquid-phase epitaxy, we present a new method to grow single-crystal Cu 2 O samples with three crystal orientations. Broadband femtosecond transient reflection spectroscopy measurements were used to quantify anisotropic optoelectronic properties, through which the carrier mobility along the [111] direction was found to be an order of magnitude higher than those along other orientations. Driven by these findings, we developed a polycrystalline Cu 2 O photocathode with an extraordinarily pure (111) orientation and (111) terminating facets using a simple and low-cost method, which delivers 7 mA cm −2 current density (more than 70% improvement compared to that of state-of-the-art electrodeposited devices) at 0.5 V versus a reversible hydrogen electrode under air mass 1.5 G illumination, and stable operation over at least 120 h. A study introduces a novel method to grow single-crystal Cu 2 O thin films with selected crystal orientations, highlighting enhanced bulk carrier mobility and carrier diffusion length along the [111] direction that yields Cu 2 O photocathodes with improved performance.

Extensive studies have focused on improving the operational stability of perovskite solar cells, but few have surveyed the fundamental degradation mechanisms. One aspect overlooked in earlier works is the effect of the atmosphere on device performance during operation. Here we investigate the degradation mechanisms of perovskite solar cells operated under vacuum and under a nitrogen atmosphere using synchrotron radiation-based operando grazing-incidence X-ray scattering methods. Unlike the observations described in previous reports, we find that light-induced phase segregation, lattice shrinkage and morphology deformation occur under vacuum. Under nitrogen, only lattice shrinkage appears during the operation of solar cells, resulting in better device stability. The different behaviour under nitrogen is attributed to a larger energy barrier for lattice distortion and phase segregation. Finally, we find that the migration of excessive PbI 2 to the interface between the perovskite and the hole transport layer degrades the performance of devices under vacuum or under nitrogen. Understanding degradation mechanisms in perovskite solar cells is key to their development. Now, Guo et al. show a greater degradation of the perovskite structure and morphology for devices operated under vacuum than under nitrogen.

Defect tolerance is a critical enabling factor for efficient lead-halide perovskite materials, but the current understanding is primarily on band-edge (cold) carriers, with significant debate over whether hot carriers can also exhibit defect tolerance. Here, this important gap in the field is addressed by investigating how intentionally-introduced traps affect hot carrier relaxation in CsPbX 3 nanocrystals (X = Br, I, or mixture). Using femtosecond interband and intraband spectroscopy, along with energy-dependent photoluminescence measurements and kinetic modelling, it is found that hot carriers are not universally defect tolerant in CsPbX 3 , but are strongly correlated to the defect tolerance of cold carriers, requiring shallow traps to be present (as in CsPbI 3 ). It is found that hot carriers are directly captured by traps, instead of going through an intermediate cold carrier, and deeper traps cause faster hot carrier cooling, reducing the effects of the hot phonon bottleneck and Auger reheating. This work provides important insights into how defects influence hot carriers, which will be important for designing materials for hot carrier solar cells, multiexciton generation, and optical gain media. The efficiency of lead-halide perovskite photovoltaics is related to the tolerance of their band-edge charge-carriers to point defects. Here, the authors show that this tolerance can be extended to hot carriers depending on the defect energy level.

The formation of core-shell heterostructures allows direct contact of two components for more efficient energy transfer while requires exquisite lattice match. Lattice mismatch is one of the most challenging obstacles for combining two components with different phases. In this work, we develop a strategy to overcome the limitation of lattice mismatch and grow α-phase lead halide perovskites (LHPs) onto β-phase lanthanide-doped nanoparticles (LnNPs) by seeding sub-8 nm LnNPs. This LnNP@LHP heterostructure effectively passivates the surface defects of LnNPs to obtain enhanced upconversion performance and enables two-way energy transfer within the heterostructures. We identify and prove that core size along with a high reaction temperature, instead of phase, is critical to overcome the lattice mismatch. Our strategy uncovers insights into the key factor of direct growth for heterostructures and we believe the current synthesis strategy for high-quality heterostructures will have strong application potential in optoelectronics, anticounterfeiting and light detection. Lattice mismatches are a difficult obstacle in the formation of core-shell heterostructures. Here, the authors develop a strategy to overcome the lattice mismatch and grow α-phase lead halide perovskites onto β-phase lanthanide-doped nanoparticles.

Perovskite quantum dot light-emitting diodes have rapidly achieved high external quantum efficiencies of over 25%; however, hindered by limited operating stability originating from surface defects or ion migration in quantum dots. Here, we design a lattice-matched anchoring molecule, tris(4-methoxyphenyl)phosphine oxide (TMeOPPO- p ), to anchor the multi-site defects and stabilise the lattice. The target quantum dots exhibit high exciton recombination features with near-unity photoluminescence quantum yields (97%), and the as-fabricated quantum dot light-emitting diodes present a maximum external quantum efficiency of up to 27% at 693 nm, a low efficiency roll-off (over 20% at a current density of 100 mA cm −2 for the typical device) and an operating half-life of over 23,000 h. Besides, the air-processed devices maintain a maximum external quantum efficiency of over 26% with good storage stability. We expect this work to exert a profound influence on rational and on-demand molecule design for perovskite QDs, indicating great promise in optoelectronic applications. Chen et al. report a lattice-matched molecule, tris(4-methoxyphenyl) phosphine oxide, to anchor multi-site defects and stabilise the lattice of perovskite quantum dots, enabling deep-red LEDs with efficiency up to 26.91% at 693 nm. The air-processed devices can still maintain an efficiency of 26.28%.

I-V-VI 2 ternary chalcogenides are gaining attention as earth-abundant, nontoxic, and air-stable absorbers for photovoltaic applications. However, the semiconductors explored thus far have slowly-rising absorption onsets, and their charge-carrier transport is not well understood yet. Herein, we investigate cation-disordered NaBiS 2 nanocrystals, which have a steep absorption onset, with absorption coefficients reaching >10 5  cm −1 just above its pseudo-direct bandgap of 1.4 eV. Surprisingly, we also observe an ultrafast (picosecond-time scale) photoconductivity decay and long-lived charge-carrier population persisting for over one microsecond in NaBiS 2 nanocrystals. These unusual features arise because of the localised, non-bonding S p character of the upper valence band, which leads to a high density of electronic states at the band edges, ultrafast localisation of spatially-separated electrons and holes, as well as the slow decay of trapped holes. This work reveals the critical role of cation disorder in these systems on both absorption characteristics and charge-carrier kinetics. Ternary chalcogenides are gaining interest as nontoxic, stable solar absorbers. Here, the authors investigate NaBiS 2 , finding cation disorder to be a critical parameter that enables its high absorption strength and unusual charge-carrier kinetics.

Reducing interfacial non-radiative recombination at the perovskite/electron transport layer interface remains a critical challenge for achieving high performance and stable perovskite/silicon tandem solar cells. This study analyzes energy losses and design bilayer passivation for enhancing the performance and durability of tandem solar cells. Our experimental results confirm that, the bilayer passivation strategy, precisely modulates perovskite energy level alignment, reduces defect density, and suppresses interfacial non-radiative recombination. Moreover, the ALD-AlO x forms a homogeneous film on the perovskite grain surface while creating island-like structures at grain boundaries, enabling nanoscale local contact areas for subsequent PDAI 2 deposition. While serving as an ion diffusion barrier, this structure facilitates moderate n-type doping and enhances charge extraction and transport efficiency. Monolithic perovskite/silicon tandem solar cells incorporating AlO x /PDAI 2 treatment achieve a power conversion efficiency of 31.6% (certified at 30.8%), utilizing industrial silicon bottom cells fabricated with Q CELLS’ Q.ANTUM technology. Furthermore, our device exhibits 95% efficiency retention after 1000 hours of maximum power point tracking at 25 o C. Reducing non-radiative recombination at the perovskite/electron transport layer interface remains a critical challenge for achieving efficient perovskite/TOPCon silicon tandem solar cells. Here, authors employ bilayer passivation using AlOx/PDAI2 treatment, achieving device efficiency of 31.6%.

Traditional white light-emitting diodes operate by exciting phosphors using blue light-emitting diodes, leading to the absence of specific colour bands compared with the visible light region of the sunlight spectrum (400–780 nm), and excess blue light increases the risk of harmful effects on ecosystems and organisms. Here, we precisely design and regulate heterophase γ / δ -CsPb(I/Cl) 3 at the nanoscale for uniform heterophase distribution, balanced flow of charges and tunable spectrum. Then, γ / δ -CsPb(I/Cl) 3 directly excited by electricity shows full-spectrum white electroluminescence covering 400–780 nm with standard Commission Internationale de l’Eclairage coordinates of (0.33, 0.33), a Colour Rendering Index of 95, a Correlated Colour Temperature of 5829 K and a Delta u,v of −3 × 10 −4 , accompanied with balanced white light composition (Melanopic ratio = 1.004). The match indices of such five core indicators to standard sunlight reach 100%, 95% (97% for R 9 ), 99.5%, 99.97% and 99.6%, respectively, far ahead of as-fabricated commercial white light-emitting diodes. Chen et al. report a large-area white LED with sunlight-like emission by regulating the heterophase γ/σ-CsPb(I/Cl) 3 at nanoscale, in which a fraction of carriers recombines in γ-CsPbI 3 for deep-red emission, while other carriers diffuse to the heterophase interface for broadband emission.