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Metal halide perovskite solar cells have demonstrated a high power conversion efficiency (PCE), and further enhancement of the PCE requires a reduction of the bandgap-voltage offset (WOC) and the non-radiative recombination photovoltage loss (ΔVOC,nr). Here, we report an effective approach for reducing the photovoltage loss through the simultaneous passivation of internal bulk defects and dimensionally graded two-dimensional perovskite interface defects. Through this dimensionally graded perovskite formation approach, an open-circuit voltage (VOC) of 1.24 V was obtained with a champion PCE of 21.54% in a 1.63 eV perovskite system (maximum VOC = 1.25 V, WOC = 0.38 V and ΔVOC,nr = 0.10 V); we further decreased the WOC to 0.326 V in a 1.53 eV perovskite system with a VOC of 1.21 V and a PCE of 23.78% (certified 23.09%). This approach is equally effective in achieving a low WOC (ΔVOC,nr) in 1.56 eV and 1.73 eV perovskite solar cell systems, and further leads to the substantially improved operational stability of perovskite solar cells.The use of a dimensionally graded 2D perovskite interface and passivation results in perovskite solar cells with very low photovoltage loss.

Doping has been widely used to control the charge carrier concentration in organic semiconductors. However, in conjugated polymers, n-doping is often limited by the tradeoff between doping efficiency and charge carrier mobilities, since dopants often randomly distribute within polymers, leading to significant structural and energetic disorder. Here, we screen a large number of polymer building block combinations and explore the possibility of designing n-type conjugated polymers with good tolerance to dopant-induced disorder. We show that a carefully designed conjugated polymer with a single dominant planar backbone conformation, high torsional barrier at each dihedral angle, and zigzag backbone curvature is highly dopable and can tolerate dopant-induced disorder. With these features, the designed diketopyrrolopyrrole (DPP)-based polymer can be efficiently n-doped and exhibit high n-type electrical conductivities over 120 S cm −1 , much higher than the reference polymers with similar chemical structures. This work provides a polymer design concept for highly dopable and highly conductive polymeric semiconductors. In conjugated polymers, n-doping is often limited by the tradeoff between doping efficiency and charge carrier mobilities, since dopants often randomly distribute within polymers, leading to significant structural and energetic disorder. Here, the authors screen a large number of polymer building block combinations and explore the possibility of designing n-type conjugated polymers with good tolerance to dopant-induced disorder.

The development of advanced perovskite emitters has considerably improved the performance of perovskite light-emitting diodes (LEDs). However, the further development of perovskite LEDs requires ideal device electrical properties, which strongly depend on its interfaces. In perovskite LEDs with conventional p-i-n structures, hole injection is generally less efficient than electron injection, causing charge imbalance. Furthermore, the popular hole injection structure of NiO x /poly(9-vinylcarbazole) suffers from several issues, such as weak interfacial adhesion, high interfacial trap density and mismatched energy levels. In this work, we insert a self-assembled monolayer of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid between the NiO x and poly(9-vinylcarbazole) layers to overcome these challenges at the organic/inorganic heterointerfaces by establishing a robust interface, passivating interfacial trap states and aligning the energy levels. We successfully demonstrate blue (emission at 493 nm) and green (emission at 515 nm) devices with external quantum efficiencies of 14.5% and 26.0%, respectively. More importantly, the self-assembled monolayer also gives rise to devices with much faster response speeds by reducing interfacial capacitance and resistance. Our results pave the way for developing more efficient and brighter perovskite LEDs with quick response, widening their potential application scope. The hole injection and device stability rely heavily on the inorganic/organic interface in perovskite light-emitting diodes. The authors enhanced the NiO x /PVK interface with a self-assembled monolayer, resulting in blue and green devices with maximum efficiencies of 14.5% and 26.0%, respectively.

Organic photovoltaic cells using Y6 non-fullerene acceptors have recently achieved high efficiency, and it was suggested to be attributed to the charge-transfer (CT) nature of the excitations in Y6 aggregates. Here, by combining electroabsorption spectroscopy measurements and electronic-structure calculations, we find that the charge-transfer character already exists in isolated Y6 molecules but is strongly increased when there is molecular aggregation. Surprisingly, it is found that the large enhanced charge transfer in clustered Y6 molecules is not due to an increase in excited-state dipole moment, Δμ, as observed in other organic systems, but due to a reduced polarizability change, Δp. It is proposed that such a strong charge-transfer character is promoted by the stabilization of the charge-transfer energy upon aggregation, as deduced from density functional theory and four-state model calculations. This work provides insight into the correlation between molecular electronic properties and charge-transfer characteristics in organic electronic materials. The performance of Y6-containing donor-acceptor active layers in organic solar cells is highly related to the charge-transfer nature in Y6 aggregates. Here, authors study charge-transfer characteristics of excitations of isolated and aggregated Y6 molecules through electroabsorption spectroscopy.

In the pursuit of advancing the commercialization of organic solar cells (OSCs), stability emerges as a paramount challenge. Herein, we show that the electron transport connectivity is a key factor determining the electron transport and device stability of OSCs. When compared to small molecular acceptors (SMAs), the larger-size polymeric acceptors (PAs) are likely to establish an electron transport network with superior connectivity. This enhanced connectivity enables more robust electron transport during potential device degradation. Our findings indicate that PA-integrated devices sustain elevated electron mobilities, even under reduced acceptor ratios (or higher impurity doping) over prolonged device operation. Furthermore, we employ the refined Su-Schrieffer-Heeger tight-binding model, in tandem with a random electron passing test and algebraic connectivity evaluations of molecular configurations, to conclusively validate the pivotal role played by the electron transport connectivity. These revelations are poised to offer new perspectives for material choices and methodologies for improving stability of OSCs. The commercialization of organic solar cells has been hindered by the limited device stability. Here, authors show that the connectivity of electron transport network is a key factor determining electron transport and device stability, with polymeric acceptors likely to establish such a network.

Quasi‐homojunction (QHJ) organic solar cells (OSCs) offer a promising alternative architecture that combines the advantages of bulk heterojunction (BHJ) and homojunction (HJ) designs. By blending a minimal fraction of donor material (a few wt%) into a nonfullerene acceptor matrix, QHJ devices can be designed to achieve efficient charge separation and transport while avoiding the morphological complexity and instability of BHJs. This study demonstrates that Y6‐based QHJ OSCs, incorporating only 4 wt% donor content, achieve a power conversion efficiency of 7.1%. This performance enhancement is enabled by replacing the PEDOT:PSS anode with a novel self‐assembled monolayer anode, which induces vertical phase separation, positioning the donor polymer at the anode interface to enhance charge extraction. The optimized vertical morphology not only facilitates efficient charge transport but also ensures excellent stability, maintaining consistent performance across active layer thicknesses of 55–180nm. This highlights the potential of QHJ architecture to combine the simplicity of HJ with the performance advantages of BHJ. Quasi‐homojunction (QHJ) organic solar cells combine the simplicity of homojunctions with the performance benefits of bulk heterojunctions. Using only 4 wt% donor material and a novel self‐assembled monolayer anode, Y6‐based QHJ devices achieve 7.1% efficiency. The optimized vertical phase separation enhances charge extraction and stability, offering a robust design across varying active layer thicknesses.

Organic semiconductors in electronic devices usually have poor thermal conduction which could trap considerable amount of heat, inducing operational instability and reducing device lifetime, limiting commercialization potential. Despite the technological essence to understand and enhance device heat‐dissipation, related studies on organic semiconductors are very limited. In this study, the authors show that the scanning photothermal deflection technique can be employed to study the thermal transport in thin films of organic photovoltaic (OPV) polymers and bulk‐heterojunctions (BHJs), with a simple empirical correction for the extrinsic experimental configuration. Phonons are identified to dominate the thermal transport due to the low carrier mobility. For OPV semiconductors, the positive correlation between the thermal diffusivity and the molecular planarity, π–π stacking and crystallinity is demonstrated. High‐performance 2D polymers such as PM6 can possess values comparable to alloys like stainless steel. In BHJs, using a polymeric acceptor can retain high thermal diffusivities compared to fullerene and ITIC acceptors, attributed to the efficient heat transfer within the polymer chains. The results offer not only a simple, highly customizable but sensitive experimental method for thermal transport in OPV systems, but also insights into the phonon dynamics and clinical investigations for thermal stability, pushing forward strategic material design. Thermal stability of organic photovoltaics relies on high thermal diffusivity which indicates promising heatrelief capability. Scanning photothermal deflection serves as a highly sensitive probe for the thermal properties. Phonon transport in semiconducting polymers is found to increase with their planarity and π–π stacking. Using polymeric acceptors in bulk‐heterojunctions can retain efficient heat transfer along the polymer chains.

The development of semi‐transparent organic solar cells (ST‐OSCs) for building‐integrated photovoltaics is fundamentally constrained by the inherent trade‐off between transparency and efficiency. To achieve a breakthrough, it is imperative to maintain high transparency while mitigating the concomitant efficiency loss in low‐donor‐content devices. Herein, we address this challenge by implementing a strategy that optimizes dual‐channel photoelectric conversion, which synergistically integrates the respective advantages of both the heterojunction (HJ) channel and the spontaneously formed photo‐charge (SP) channel. The results reveal that the HJ channel primarily governs hole transport and thus the fill factor, whereas the SP channel is pivotal for charge generation, directly influencing the short‐circuit current density. Strategic acceptor selection and dual‐additive‐assisted morphology control effectively minimize electrical losses from insufficient charge generation and severe recombination, enabling a remarkable power conversion efficiency of 11.3% in PTB7‐Th:BTP‐eC9 (1:4) devices that outperforms their bulk heterojunction (BHJ) counterparts (10.4%), without losing the high transparency (>65%). The general applicability of this strategy was further validated in PM6:BTP‐eC9 (1:3) based ST‐OSCs, yielding a competitive light utilization efficiency of 4.67% and demonstrating the generalizability of our approach across different active layer systems. This study reveals the crucial role of dual‐channel photoelectric conversion in realizing high‐performance ST‐OSCs. The respective roles of the heterojunction (HJ) and spontaneously formed photo‐charge (SP) channels in low‐donor‐content devices have been decoupled and subjected to a targeted optimization strategy. A breakthrough of light utilization efficiency (LUE) in semi‐transparent organic solar cells (ST‐OSCs) is achieved.

This thesis describes the interaction of low energy photons (1-5 eV) with adsorbed molecules on surfaces of single crystals under ultrahigh vacuum conditions. This subject of study is important in understanding the fundamental mechanisms of photon induced reactions on surfaces. Low power (1-4000 mW), cw radiation was used to induce desorption and/or dissociation of adsorbed molecules. The surface before and after photon irradiation was characterized by thermal desorption spectroscopy and high resolution electron energy loss spectroscopy, and electronic electron energy loss spectroscopy. Molybdenum hexacarbonyl (Mo(CO) $\\sb6$ ) interacts weakly with Ag(111) and the basal plane of graphite. The electronic structure of the molecule is found to differ little from that of the gas phase. Photodissociation of Mo(CO) $\\sb6$occurs under low power UV irradiation. In contrast to the gas phase, the photodissociation is incomplete due to the presence of the substrate. The photodissociation spectra of different coverages of Mo(CO) $\\sb6$are shown to resemble that of the gas phase. The mechanism of photodissociation is identified to be the direct photoelectronic excitation of the adsorbed molecule. In the case of Ag(111), enhanced photodissociation appears near 325 nm due to enhanced surface electric field associated with the$d$ -band to the Fermi level transition. In contrast, both photodesorption and photodissociation occur for NO adsorbed on GaAs(110) under visible photon irradiation. By considering the photon power and wavelength dependences, the photoreaction mechanism is attributed to a substrate mediated mechanism involving photogenerated hot carriers interacting with the adsorbed NO. On the noble metal surfaces (Ag(111) and Cu(111)), only photodesorption of NO occurs. A more weakly adsorbed NO species is selectively photodesorbed. A photoreaction mechanism involving photogenerated hot carriers can be used to explain the photodesorption for photon energies$<$ 3 eV. For higher photon energies, additional reaction channels, which can be related to excitation of the NO adsorbate-surface complex, become available for photoreactions.

Sodium‐ion batteries (SIBs) are considered as a low‐cost complementary or alternative system to prestigious lithium‐ion batteries (LIBs) because of their similar working principle to LIBs, cost‐effectiveness, and sustainable availability of sodium resources, especially in large‐scale energy storage systems (EESs). Among various cathode candidates for SIBs, Na‐based layered transition metal oxides have received extensive attention for their relatively large specific capacity, high operating potential, facile synthesis, and environmental benignity. However, there are a series of fatal issues in terms of poor air stability, unstable cathode/electrolyte interphase, and irreversible phase transition that lead to unsatisfactory battery performance from the perspective of preparation to application, outside to inside of layered oxide cathodes, which severely limit their practical application. This work is meant to review these critical problems associated with layered oxide cathodes to understand their fundamental roots and degradation mechanisms, and to provide a comprehensive summary of mainstream modification strategies including chemical substitution, surface modification, structure modulation, and so forth, concentrating on how to improve air stability, reduce interfacial side reaction, and suppress phase transition for realizing high structural reversibility, fast Na+ kinetics, and superior comprehensive electrochemical performance. The advantages and disadvantages of different strategies are discussed, and insights into future challenges and opportunities for layered oxide cathodes are also presented. Recent progress in layered oxide cathodes for sodium‐ion batteries (SIBs) from air stability, interface chemistry, and phase transition are comprehensively summarized. The intrinsic degradation mechanisms behind electrochemical performance and mainstream modification strategies are systematically sorted out and analyzed. The remaining challenges, promising optimization strategies as well as endeavor directions to break current limitations are also presented for the future design of high‐performance layered oxide cathodes for SIBs.