以昇陳

Surface passivation reduces non-radiative charge recombination and interfacial charge accumulation in perovskite photovoltaics. Carbazole, functionalized with ammonium iodide and alkyl chains, forms hydrophobic passivation layers on FAPbI₃ perovskite films, improving stability and efficiency. This approach minimizes trap-assisted recombination and enhances hole transfer, achieving 24.8% PCE and maintaining 95% of its initial efficiency after 1000 h under the ISOS-L1 protocol.

Abstract

Surface passivation has been widely employed to suppress non-radiative charge recombination and prevent interfacial charge accumulation in perovskite photovoltaics. In this report, carbazole modified with ammonium iodide connected via alkyl chains of different lengths (i.e., ethyl, butyl, and hexyl chains) is used to form passivation layers on formamidinium lead triiodide FAPbI₃-based perovskite films to improve operational stability. Owing to the strong hydrophobicity of the carbazole moiety, it is observed that the perovskite films with a carbazole passivation layer retain their initial properties even after direct contact with a water droplet for 100 s. In addition, carbazole treatment reduces the rate of trap-assisted recombination at the surface and grain boundaries of the perovskite layer. Furthermore, it accelerates interfacial hole transfer from the perovskite to the charge transport layer. As a result, devices treated with carbazole hexylammonium iodide achieve a power conversion efficiency (PCE) of up to 24.3% during quasi-steady-state (QSS) measurements with extraordinary long-term operational stability under conditions of the ISOS-L-1 protocol, maintaining 95% of their initial efficiency after 1000 h.

The cooling mechanism of hot carriers in 2D/3D metal halide perovskites is found to be modulated by electron–phonon coupling between bending and stretching phonon branches. The coupling depends on quantum confinement, with high frequency modes dominating for confined systems.

Abstract

The cooling mechanism of hot carriers (HC) in metal halide perovskites is a topic of debate which gathered huge attention due to its critical role in the performance of perovskite-based optoelectronics. HC cooling in 2D perovskites is faster than in its 3D counterpart, whereas in 2D/3D perovskites cooling becomes faster with decreasing the thickness of the inorganic quantum wells. Using state-of-the art first principles calculations it is showed that the modulation of electron–phonon (e-ph) coupling strength between bending and stretching phonon branches can explain this observation. Starting from the prototype BA₂PbI₄ and PEA₂PbI₄ 2D perovskites, e-ph coupling of individual phonon modes is investigated for 2D/3D perovskites with n = 1 and 3, along with a vis-à-vis comparison with the prototypical 3D MAPbI₃ system. This study shows that e-ph coupling with high-frequency stretching phonon modes in the 60–120 cm⁻¹ range is highest for n = 1 while it decreases with increasing the quantum well layers, by approaching the 3D bulk limit where e-ph coupling with low-frequency bending phonon modes (<60 cm⁻¹) is dominant. Longer spacer cations with identical quantum well structures have a limited impact on the e-ph coupling, highlighting that the primary factor governing HC cooling is the quantum confinement within the inorganic sublattice. This study provides an advancement in the understanding of the mode-specific e-ph mediated HC cooling mechanism in metal-halide perovskites and can provide a route map toward tuning the e-ph interaction, which is instrumental for effectively gathering HC in solar cell devices.

The state-of-the-art PSCs employ α-FAPbI₃ in spite of its metastable crystalline phase at RT. In this review, the intrinsic structural stability of α-FAPbI₃ is discussed from the collective perspective based on various experimental results which are closely examined to understand fundamental origins and their role in maintaining the lattice structure, particularly by assessing the contribution between entropy and enthalpy term.

Abstract

Since the certified power conversion efficiency (PCE) of perovskite solar cells (PSCs) has reached 26.1%, exactly equal to that of crystalline silicon solar cells, a strong demand for ensuring the long-term stability of PSCs has arisen for commercialization. The intrinsic stability of the perovskite layer must be guaranteed as a top priority to ensure the whole device's stability. Recently, the state-of-the-art PSCs, performing a high PCE, employ α-FAPbI₃ (FA = formamidinium) for the perovskite layer in spite of its metastable tendency to spontaneously transform into its photoinactive polymorph at PSC operating temperature. In this review paper, the intrinsic structural stability of α-FAPbI₃ soft lattice is understood from the thermodynamic point of view, with key parameters to restrain the undesirable phase transition. Besides, reported experimental results are closely examined to find fundamental origins, derive the enhanced phase stability in each experiment, and understand their role in maintaining the lattice structure from the collective perspective.

Nature Photonics, Published online: 09 January 2025; doi:10.1038/s41566-024-01570-4

A mixed post-treatment strategy combining 2-thiopheneethylammonium chloride and ethylenediamine is proposed to modify the perovskite surface, promote the formation of a pure-phase 2D layer, and homogenize the surface potential. This approach results in hybrid evaporation-solution-processed perovskite solar cells with a power conversion efficiency of 24.20% and the lowest open-circuit voltage deficit of just 0.36 V.

Abstract

Perovskite solar cells (PSCs) have garnered significant attention for their outstanding optoelectronic properties, yet surface defects remain a major obstacle to achieving optimal performance, especially in scalable hybrid evaporation-solution fabrication methods. Conventional passivation techniques often struggle with shallow penetration of passivation agents, limiting their effectiveness. Here, an advanced post-treatment strategy is introduced that synergistically combines 2-thiopheneethylammonium chloride with a trace amount of ethylenediamine to achieve superior surface passivation. ethylenediamine acts as a “penetration facilitator,” mildly etching the perovskite surface and enabling deeper infiltration of 2-thiopheneethylammonium chloride, which results in the formation of a uniformly distributed and pure-phase 2D perovskite layer. This deeply penetrating passivation layer effectively suppresses nonradiative recombination at the perovskite/electron transport layer interface. As a result, inverted PSCs fabricated using the hybrid evaporation-solution method achieved a power conversion efficiency of 24.20%, accompanied by an open-circuit voltage of 1.189 V and an open-circuit voltage deficit of 0.36 V. Additionally, this post-treatment strategy demonstrates broad performance enhancements across PSCs with various bandgaps and fabrication methods, offering a versatile and promising pathway to boost both the efficiency and stability of PSCs.

TADF sensitizers targeting deep-blue emitters are designed by combining the advantages of short-range and long-range charge-transfer excited states. The resulting sensitizers enable high-performance deep-blue OLEDs with BT. 2020 blue gamut together with external quantum efficiency approaching 40%.

Abstract

The hyperfluorescence (HF) technology holds great promise for the development of high-quality organic light-emitting diodes (OLEDs) for their excellent color purity, high efficiency, and low-efficiency roll-off. Sensitizer plays a crucial role in the performance of HF devices. However, designing sensitizers with simultaneous high photoluminescence quantum yield (PLQY), rapid radiative decay (k _r), and fast reverse intersystem crossing rate (k _RISC) poses a great challenge, particularly for the thermally activated delayed fluorescence (TADF) sensitizers targeting deep-blue HF device. Herein, by introducing a boron-containing multi-resonance-type acceptor into the multi-tert-butyl-carbazole encapsulated benzene molecular skeleton, two TADF emitters featuring hybridized multi-channel charge-transfer pathways, including short-range multi-resonance, weakened through-bond, and compact face-to-face through-space charge-transfer. Benefiting from the rational molecular design, the proof-of-concept sensitizers exhibit simultaneous rapid k _r of 5.3 × 10⁷ s⁻¹, fast k _RISC up to 5.9 × 10⁵ s⁻¹, a PQLY of near-unity, as well as ideal deep-blue emission in both solution and film. Consequently, the corresponding deep-blue HF devices not only achieve chromaticity coordinates that fully comply with the latest BT. 2020 standards, but also showcase record-high maximum external quantum efficiencies nearing 40%, along with suppressed efficiency roll-off.

Vacuum-processable TAA-tetramer is introduced as a hole-transport layer (HTL) in all-vacuum-processed inverted perovskite solar cells (PSCs). Through the reduced structure, energy disorder, and improved surface features of the HTL, enhanced performance and operational stability of the PSCs are realized. Furthermore, large-area single cells and modules are successfully demonstrated with minimal efficiency loss during their scale-up.

Abstract

As perovskite solar cells (PSCs) require higher standards for commercial applications, all vacuum-processed PSCs should become a key in future manufacturing processes of scalable PSCs compared to their currently dominating research types based on solution processes. In fact, vacuum deposition of high-quality organic hole-transport layers (HTLs) is crucial for successful fabrication of all vacuum-processed scalable PSCs. Here, the study develops a triarylamine-based single oligomer (TAA-tetramer)−a miniaturized-molecular form of the well-known poly(triarylamine) (PTAA)−as a vacuum-processable HTL in inverted PSCs. The well-defined structure and monodisperse nature of the TAA-tetramer render strong intermolecular π−π interactions and/or molecular ordering, resulting in simultaneously enhanced quasi-Fermi level splitting and hole-transport efficiency of the perovskite. The resulting all-vacuum-processed inverted PSCs exhibits a high power conversion efficiency (PCE) of 23.2%, which is record-high performance reported among all-vacuum-processed PSCs, with exceptional device stabilities. Furthermore, the all-vacuum-deposition process allows the fabrication of efficient PSCs and modules with reliable scalability and minimized efficiency loss during scale-up. Notably, the proposed HTL enabled high-efficiency large-area (25 cm²) single-PSC with a PCE of 12.3%, representing one of the largest active areas and the highest performance ever reported for the large-area device. A promising strategy for developing efficient, stable, and scalable PSCs for all-vacuum processes is presented.

Sterical aryl immobilizing groups are incorporated (phenyl and pyridine) at the C8 site of the rigid fluorene spacer. These immobilizing groups restrict both rotational and rocking motions. The completely confined conformation demonstrates enhanced TADF performance.

Abstract

Intramolecular through-space charge-transfer (TSCT) excited states have emerged as promising candidates for thermally activated delayed fluorescence (TADF) emitters. This study addresses the challenges in tuning excited state dynamics through conformational engineering, which significantly impacts exciton utilization. An effective strategy is presented to enhance the performance of TSCT-TADF molecules by restricting the lateral rocking of the spiro unit via immobilizing groups, which indirectly adjusts the conformations of the donor and acceptor subunits. This approach is successfully illustrated with two TSCT-TADF emitters, 8PhDM-B and 8PyDM-B, featuring sterical aryl phenyl and pyridine substitutions at the C8 site of a rigid spiro-fluorene bridge. Organic light-emitting diodes (OLEDs) utilizing these emitters demonstrated impressive maximum external quantum efficiencies of 33.1% and 31.0%, respectively. The findings underscore the importance of the rocking confined strategy in refining excited state dynamics, thereby providing valuable insights for the design of highly efficient OLED emitters.

Nicotinamide derivatives with multi-functional groups modulate crystal growth and mitigate defects in wide-bandgap perovskite, favoring the photovoltaically preferred (100) facet and energy band alignment, enabling efficient and stable single-junction wide-bandgap and all-perovskite tandem solar cells with efficiencies of 19.34% and 28.57%, respectively.

Abstract

Wide-bandgap perovskite solar cells (WBG PSCs) have promising applications in tandem devices yet suffer from low open-circuit voltages (V _OCs) and less stability. To address these issues, the study introduces multifunctional nicotinamide derivatives into WBG PSCs, leveraging the regulation on photovoltaically preferential orientation and optoelectronic properties via diverse functional groups, e.g., carbonyl, amino. Isonicotinamide (IA) molecule emerges as the most effective agent, enhancing crystallization kinetics and defect passivation due to its unique planar spatial configuration. Incorporating IA into WBG perovskites improves the (100) preferred crystal orientation, reduces trap density, and enables well-matched energy band alignment. High-performance 1.77 eV WBG PSCs are achieved with a champion power conversion efficiency of 19.34% and a V _OC of 1.342 V, leading to the fabrication of the best-performing all-perovskite tandem solar cell with a PCE of 28.53% (certified 28.27%) and excellent operational stability, maintaining over 90% of the initial efficiency under 1 sun illumination for 600 h.

This work describes the development of a non-volatile optical memristor enabled by the electro-optic (EO) effect in ferroelectric PMN-PT, which supports deterministic, repeatable multilevel EO states for phase modulation. A tunable waveplate achieving phase shifts from 0 to π/2 is presented, demonstrating the potential of relaxor ferroelectrics in non-volatile memory and photonic networks.

Abstract

Memristors enable non-volatile memory and neuromorphic computing. Optical memristors are the fundamental element for programmable photonic integrated circuits due to their high-bandwidth computing, low crosstalk, and minimal power consumption. Here, an optical memristor enabled by a non-volatile electro-optic (EO) effect, where refractive index modulation under zero field is realized by deliberate control of domain alignment in the ferroelectric material Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃(PMN-PT) is proposed. The non-volatile EO memristor is designed exclusively for the modulation of the optical phase without degrading the optical transparency, and it allows the support for deterministic and repeated non-volatile multilevel EO states. A non-volatile tunable waveplate composed of the optical memrisor for free-space optics, which allows for deterministic multilevel, and non-volatile phase shifts from 0 to π/2 is presented. The state switching rate of the memristor is less than 100 ms, with a switching energy consumption of 234 nJ, and the states can be retained for up to 12 h without requiring static power consumption. These results demonstrate a novel approach to fully realizing non-volatile optical memristors, where only optical phase modulation is involved, providing unprecedented opportunities for the development of new ferroelectric memristors.

The formation dynamics of low-dimensional perovskites derived from N-methyl-1-(naphthalen-1-yl)methanamine hydroiodide (M-NMAI) are studied. The exclusively produced thermally stable 1D structure on 3D perovskite films other than heterogeneous nucleation preferred Ruddlesden–Popper 2D perovskite structure benefits the resulting n-i-p perovskite solar cells to achieve a peak efficiency of 25.51% with significantly enhanced thermal stability.

Abstract

Direct understanding of the formation and crystallization of low-dimensional (LD) perovskites with varying dimensionalities employing the same bulky cations can offer insights into LD perovskites and their heterostructures with 3D perovskites. In this study, the secondary amine cation of N-methyl-1-(naphthalen-1-yl)methylammonium (M-NMA⁺) and the formation dynamics of its corresponding LD perovskite are investigated. The intermolecular π–π stacking of M-NMA⁺ and their connection with inorganic PbI₆ octahedrons within the product structures control the formation of LD perovskite. In an N,N-dimethylformamide (DMF) precursor solution, both 1D and 2D products can be obtained. Interestingly, due to the strong interaction between M-NMA⁺ and the DMF solvent, compared to the 1D phase, the formation of 2D perovskites is uniquely dependent on heterogeneous nucleation. Nevertheless, post-treatment of 3D perovskite films with an isopropanol solution of M-NMAI leads to the exclusive formation of thermally stable 1D phases on the surface. The resulting 1D/3D heterostructure facilitates perovskite solar cells (PSCs) to not only achieve a record efficiency of 25.51% through 1D perovskite passivation but also significantly enhance the thermal stability of unencapsulated devices at 85 °C. This study deepens the understanding of the formation dynamics of LD perovskites and offers an efficient strategy for fabricating stable and high-performance PSCs.

A multifunctional additive of 8-pentafluorobenzyloxy quinoline (8-PFBQ) is explored to promote the performance of wide-bandgap perovskite solar cells. The roles of 8-PFBQ in improving the crystallinity and homogenizing the halide components in wide-bandgap perovskite films are comprehensively revealed. Efficient wide-bandgap perovskite solar cells with a high power conversion efficiency of 22.22% and a two-fold enhancement in operational stability are achieved.

Abstract

Wide-bandgap perovskite solar cells, which are essential for tandem photovoltaics, easily suffer from open-circuit voltage (V _OC) losses due to challenges in suppressing halogen heterogeneity and defect-related nonradiative recombination in the active layers. Herein, a multifunctional fluorine-containing additive of 8-pentafluorobenzyloxy quinoline (8-PFBQ) is explored to modulate the crystallization and defect properties of wide-bandgap (1.67 eV) perovskites, enhancing both efficiency and operational stability of ensuing solar cells. It is demonstrated that the quinoline group of 8-PFBQ can strongly coordinate with the lead ions and the fluorinated benzyl group effectively interacts with the organic halides through anion-π and hydrogen bonding interactions simultaneously. These synergistic effects improve crystal quality and composition homogeneity, holistically reducing defects in the perovskite active layers. The resulting wide-bandgap solar cells achieve a champion power conversion efficiency of 22.22%, featuring a high V _OC of 1.243 V and a two-fold enhancement in the operational stability. This work presents an alternative strategy for defect management in wide-bandgap perovskites, offering insights for advancements in both single-junction and tandem photovoltaics.

A vacuum-assisted heating treatment strategy is proposed to regulate the high-purity photoactive phase in the mixed cationic perovskite. The interface defects are passivated with buried interface modification and the carrier transport is improved. This work provides a straightforward method for the reproducible fabrication of FA-based perovskite, and can pave the way for the flexible imaging sensing system.

Abstract

Regulating the crystallization process of organic–inorganic halide perovskite is essential for the fabrication of reproducible and efficient optoelectronic devices. Herein, a vacuum-assisted heating treatment strategy for precursor is developed to obtain a high-purity photoactive phase perovskite. By eliminating residual H₂O molecules from raw materials and solvents, the method prevents the Pb–I framework of perovskite from being destroyed. Additionally, the pre-treated precursor possesses high-valence iodoplumbate species leading to preferable crystallization for perovskite films. Furthermore, a high on-off ratio of 1103 is attained under 0 V and 550 nm illumination by employing a vertical n–i–p photodetector based on pure 𝛼-phase perovskite films and interface passivation carried out by incorporating phenethylammonium hydroiodide (PEAI) in the n-type electron transport layer. The photodetector exhibits high sensitivity with the peak responsivity of 0.93 A W⁻¹ and the detectivity of 1.55 × 10¹² Jones in the visible light range, making it a potential candidate for an imaging application. The flexible photodetector fabricated on polyethylene terephthalate (PET) substrate maintains 98.6% photocurrent density after 300 times of bending and preliminarily realizes imaging sensing. The heat-treating strategy improves the adaptability of perovskite to complex environments and enables the preparation of reproducible pure 𝛼-phase perovskite films, which boast enormous potential for optoelectronic applications.

An MR-TADF dendrimer, 2GtBuCzCO₂HDCzB, features an encapsulated MR-TADF core surrounded by a donor-acceptor TADF moiety containing donor dendrons. The non-doped SP-OLEDs with 2GtBuCzCO₂HDCzB exhibit narrowband green emission peaking at 495 nm (FWHM of 30 nm) and show an EQE_max at 24.0% and small efficiency roll-off, with EQE₁₀₀₀ of 20.2%.

Abstract

The development of narrowband emissive, bright, and stable solution-processed organic light-emitting diodes (SP-OLEDs) remains a challenge. Here, a strategy is presented that merges within a single emitter a TADF sensitizer responsible for exciton harvesting and an MR-TADF motif that provides bright and narrowband emission. This emitter design also shows strong resistance to aggregate formation and aggregation-cause quenching. It is based on a known MR-TADF emitter DtBuCzB with a donor-acceptor TADF moiety consisting of either tert-butylcarbazole donors (tBuCzCO₂HDCzB) or second-generation carbazole-based donor dendrons (2GtBuCzCO₂HDCzB) and a benzoate acceptor. The TADF moiety acts as an exciton harvesting antenna and transfers these excitons via Förster resonance energy transfer to the MR-TADF emissive core. The SP-OLEDs with 2GtBuCzCO₂HDCzB and tBuCzCO₂HDCzB thus show very high maximum external quantum efficiencies (EQE_max of 27.9 and 22.0%) and minimal efficiency roll-off out to 5000 cd m⁻².

Schematic illustrating the two dominant processes in tin-iodide perovskites at the band edge: 1) Filling of carriers at the band edge extrema as they cool. 2) Cooling of carriers emitting a longitudinal optical (LO) phonon. The inset shows the dephasing of a longitudinal optical phonon studied by impulsive vibrational spectroscopy in this work.

Abstract

Metal halide perovskites have shown exceptionally slow hot-carrier cooling, which has been attributed to various physical mechanisms without reaching a consensus. Here, experiment and theory are combined to unveil the carrier cooling process in formamidinium (FA) and caesium (Cs) tin triiodide thin films. Through impulsive vibrational spectroscopy and molecular dynamics, much shorter phonon dephasing times of the hybrid perovskite, which accounts for the larger blueshift in the photoluminescence seen at high excitation density for FASnI₃ compared to CsSnI₃ is reported. Density functional theory investigations reveal that the largest contribution to the blueshift is accounted by a giant, dynamic band-filling effect in Sn-based perovskites, which in turn can explain the cooling disparity with the Pb-based counterparts. Several years after the first experimental observations, here a deeper understanding of the cooling mechanism of these materials is provided. Design principles for hot-carrier materials, which may be useful for future implementations of hot-carrier solar cells are further provided.

This work demonstrates that the introduction of heterogeneous amine as peripheral groups in hole-transport molecule is efficient to improve the efficiency and durability of perovskite solar cells. The newly developed spirobifluorene derivative bearing methoxynaphthalene and 9,9-dimethylfluorene heterogeneous amine peripheral groups enables devices with a champion efficiency of 24.66% and an open-circuit voltage of 1.19 V, and high operational stability under harsh conditions.

Abstract

Achieving efficient perovskite solar cells (PSCs) with high operational durability is a challenging task. Here, by exploiting the heterogeneous amine strategy at the molecular level, a novel spirobifluorene derivative bearing methoxynaphthalene and 9,9-dimethylfluorene heterogeneous amine peripheral groups (N ²,N ^2′,N ⁷,N ^7′-tetrakis(9,9-dimethyl-9H-fluoren-2-yl)-N ²,N ^2′,N ⁷,N ^7′-tetrakis(6-methoxynaphthalen-2-yl)-9,9′-spirobi[fluorene]-2,2′,7,7′-tetraamine, denoted as Spiro-NADF) as a hole transport material (HTM) is developed to address the efficiency and durability issues of PSCs. Compared with 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl)-amine-9,9′-spirobifluorene, Spiro-NADF exhibits not only favorable energy level alignment but also a higher glass transition temperature and strong adhesion to perovskite. Moreover, Spiro-NADF-based transport layer shows excellent morphological stability in devices against damp heat stress. These advantages reduce voltage loss and suppress perovskite decomposition and ion migration. Consequently, PSCs based on Spiro-NADF exhibit a champion efficiency of 24.66% with an open-circuit voltage of 1.19 V. The corresponding cells show greatly enhanced operational durability against harsh environments, retaining over 92% of the initial efficiencies for 500 h aging under a damp heat test (85 °C and 70–90% relative humidity) and illumination under the maximum power point tracking, respectively. This work demonstrates that molecular engineering of HTMs using heterogeneous amines with polycyclic aromatics leaves considerable room for developing efficient and stable PSCs.

The efficiency of perovskite solar cells fabricated using the evaporation method is often limited by incomplete reactions and small grain sizes. The combination of guanidine thiocyanate and methylammonium iodide in the precursors addresses these challenges. The resulting hybrid evaporation-solution-processed perovskite solar cells achieve a remarkable efficiency of 24.72% with a low open-circuit voltage loss of 0.377 V.

Abstract

Perovskite solar cells (PSCs) represent a promising technology for next-generation photovoltaics, yet scaling up from laboratory to industrial production via the solution spin-coating method encounters significant challenges. Vacuum deposition offers a potential alternative but struggles with controlling perovskite phases and ensuring sufficient precursor reactions. Here, the study presents a hybrid evaporation-solution approach using a large cation-based pseudo-halogen anion salt (guanidine thiocyanate) and a compensating cation salt (methylammonium iodide) as co-additives to finely modulate the phase transition process. This approach eliminates the need for intermediate-phase transitions, promotes sufficient precursor reactions, and facilitates the formation of highly oriented α-phase perovskites prior to annealing. Consequently, it prevents detrimental δ-phase formation, yielding enlarged, homogeneous perovskite grains with significantly reduced defects. The resulting p-i-n-structured PSCs achieve a maximum efficiency of 24.72% and a low open-circuit voltage loss of 0.377 V, coupled with significantly improved stability. The work integrates the advantages of vacuum deposition and solution processing, providing new insights into perovskite phase transitions and paving the way for the efficient, scalable production of high-performance PSCs.

In this study, B₂O₃ coating layer is used as a flux for Sb₂Se₃ recrystallization, inducing a vertical orientation growth of the film while suppressing the defect of Se vacancies. The orientation control and passivation of defects enables efficient transport of carriers, resulting in the highest efficiency in Sb₂Se₃ solar cells fabricated by thermal evaporation method.

Abstract

Crystallization process is critical for enhancing the crystallinity, regulating the crystal orientation of polycrystalline thin films, as well as repairing defects within the films. For quasi-1D Sb₂Se₃ photovoltaic materials, the preparation of Sb₂Se₃ thin films still faces great challenges in adjusting orientation and defect properties, which limits the device performance. In this study, a novel post-treatment strategy is developed that uses a low melting point B₂O₃ coating layer as a flux to drive the recrystallization of Sb₂Se₃, thereby regulating the micro-orientation of thermal evaporation-derived Sb₂Se₃ films and optimizing their electrical properties. Mechanistic investigations show that B₂O₃ exhibits stronger adsorption with (hk1) planes of Sb₂Se₃ to induce a vertical orientation growth of the film, while blocking the volatilization channels of Se and inhibiting Se vacancy defects by interacting with Sb₂Se₃. The Sb₂Se₃ film with [hk1] preferential orientation and suppressed deep-level defects promotes the effective transport of charge carriers in solar cells. As a result, the B₂O₃-treated device delivers a champion efficiency of 9.37% without MgF₂ anti-reflection coating, which is currently the highest efficiency in Sb₂Se₃ solar cells achieved by thermal evaporation method. This study provides a new method and mechanism for regulating optical and electrical properties of low-dimensional inorganic thin films.

A stable lead-free perovskite, dimethylamine bismuth iodide (DMABI), demonstrates exceptional UVC photodetection. The device exhibits ultralow dark current, high on/off ratio, superior detectivity, and low operating voltage. With high responsivity and external quantum efficiency, DMABI emerges as a promising candidate for high-performance, low-cost deep UV photodetectors, outperforming existing materials in key performance metrics.

Abstract

Ultraviolet (UV) photodetectors (PDs) are essential for various applications, but traditional materials face challenges in cost, fabrication, and performance. This study introduces dimethylamine bismuth iodide (DMABI) as a promising lead-free perovskite for UV PDs, particularly in the UVC region. DMABI demonstrates exceptional device parameters, including an ultralow dark current of 0.12 pA at 0.05 V, a high on/off ratio of 7.1 × 10⁴, and a peak detectivity of 3.18 × 10¹³ Jones. The unique structure of DMABI, with isolated octahedral units, ensures minimal connectivity, significantly reducing dark current. When exposed to high-energy UV light, carriers gain sufficient energy to hop between octahedrally coordinated bismuth centres, resulting in substantial photocurrent. The small size of the organic cation facilitates efficient charge transfer, contributing to high responsivity (1.46 A W⁻¹) and external quantum efficiency (up to 717%). These results establish DMABI as a superior, low-cost candidate for UV photodetection, addressing limitations of existing materials. The study provides insights into the molecular mechanisms driving these characteristics and highlights potential for future advancements in UV PD technology.

This study proposes an advanced design concept for matrix-free hyperfluorescent systems, utilizing anti-quenching TADF materials as hosts to overcome aggregation-induced challenges in traditional MR-TADF emitters by regulating the energy transfer process. Importantly, this strategy avoids complex chemical modifications of MR-TADF emitters, making them universal and low-cost, which will greatly promote the commercialization of hyperfluorescent OLEDs.

Abstract

Organic light-emitting diodes (OLEDs) based on hyperfluorescent system have attracted widespread attention due to their ability to simultaneously achieve improvements in efficiency, lifetime, and color purity by combining the advantages of high exciton utilization sensitizers and high-color purity emitters. Traditional hyperfluorescent systems typically involve three or four components and are severely sensitive to the doping concentration (≈0.5 wt%) of a terminal emitter, which inevitably causes high costs and difficulties in reproducibility. Here, a novel design concept for a matrix-free hyperfluorescent (MFHF) system that employs a combination of an anti-quenching TADF host and a high color purity MR-TADF emitter is proposed. This strategy allows traditional concentration-sensitive MR-TADF emitters to significantly improve exciton utilization and reduce exciton lifetime at high doping levels, without the need for complex molecular modifications. The OLEDs with binary emissive layer achieve pure-green emission, a maximum external quantum efficiency of over 30%, and a high maximum power efficiency of 145 lm W⁻¹. The approach offers a straightforward and universal method to achieve anti-quenching matrix-free hyperfluorescent OLEDs with high color purity, making them promising for commercial applications in low-cost ultra-high-definition (UHD) displays.