Near-infrared absorbing acceptor with suppressed triplet exciton generation enabling high performance tandem organic solar cells

Phenazine-Based Ultra-Narrow Bandgap Acceptors for Efficient Transparent Organic Photovoltaic

Developing ultra-narrow bandgap electron acceptors is an effective approach to achieving transparent organic photovoltaics (TOPVs). In this study, two phenazine based non-fullerene acceptors, namely PA-2H and PA-2Br, are synthesized by merging core bromination and extended conjugation. Applying extra ethylene double bonds as π bridge makes the absorption onsets of films red shift to 1021 and 1041 nm for PA-2H and PA-2Br, respectively. Single-crystal data illustrated that PA-2Br exhibits a tight and ordered 3D network packing with improved charge transport, different from the 2D step-like packing of PA-2H. Therefore, PA-2Br-based opaque organic photovoltaics achieves an excellent power conversion efficiency (PCE) of 13.7%. Notably, the TOPV attains a PCE of 4.60% with an average visible transmittance (AVT) of 70.2%, which exhibits promise in efficient TOPVs. This work demonstrates the importance of core bromination in the design of high-performance ultra-narrow bandgap electron acceptors and provides the opportunity to fabricate efficient TOPVs.

Multiple-Asymmetric Molecular Engineering Enables Regioregular Selenium-Substituted Acceptor with High Efficiency and Ultra-low Energy Loss in Binary Organic Solar Cells

Asymmetric molecular engineering is utilized for developing efficient small molecular acceptors (SMAs), whereas adopting multiple asymmetric strategies at the terminals, side chains, and cores of efficient SMAs remains a challenge, and effects on reducing energy loss (Eloss) have been rarely investigation. Herein, four regioregular multiple-asymmetric SMAs (DASe-4F, DASe-4Cl, TASe-2Cl2F, and TASe-2F2Cl) are constructed by delicately manipulating the number and position of F and Cl on end groups. Triple-asymmetric TASe-2F2Cl not only exhibits a unique and most compact 3D network crystal stacking structure but also possesses excellent crystallinity and electron mobility in neat film. Surprisingly, the PM1:TASe-2F2Cl-based binary organic solar cells (OSCs) yield a champion power conversion efficiencies (PCEs) of 19.32%, surpassing the PCE of 18.27%, 17.25%, and 16.30% for DASe-4F, DASe-4Cl, and TASe-2Cl2F-based devices, which attributed to the optimized blend morphology with proper phase separation and more ordered intermolecular stacking and excellent charge transport. Notably, the champion PCE of 19.32% with ultralow nonradiative recombination energy loss (ΔE3) of 0.179 eV marks a record-breaking result for selenium-containing SMAs in binary OSCs. Our innovative multiple-asymmetric molecular engineering of precisely modulating the number and position of fluorinated/chlorinated end groups is an effective strategy for obtaining highly-efficient and minimal ΔE3 of selenium-substituted SMAs-based binary OSCs simultaneously.

An n-Doped Organic Cross-Linked Electron Transport Layer with High Electrical Conductivity for High-Efficiency Tandem Organic Photovoltaics

With merits of good solution processability, intrinsic flexibility, etc, organic/organic interconnecting layers (ICLs) are highly desirable for tandem organic photovoltaics (OPVs). Herein, an n-doped cross-linked organic electron transport layer (ETL), named c-NDI-Br:PEI is developed, via a simple in situ quaternization reaction between bromopentyl-substituted naphthalene diimide derivative (NDI-Br) and polyethylenimine (PEI). Due to strong self-doping, c-NDI-Br:PEI films exhibit a high electrical conductivity (0.06 S cm-1), which is important for efficient hole and electron reombination in ICL of tandem OPVs. In addition, the cross-linked ETLs show strong work function modulation ability, and good solvent-resistance. The above features enable c-NDI-Br:PEI to function as an efficient ETL not only for single-junction OPVs, but also for tandem devices without any metal layer in ICL. Under solar radiation, the single-junction device with c-NDI-Br:PEI as ETL achieves a power conversion efficiency (PCE) of 18.18%, surpassing the ZnO-based device (17.09%). The homo- and hetero-tandem devices with m-PEDOT:PSS:c-NDI-Br:PEI as ICL exhibit remarkable PCEs of 19.06% and 20.06%, respectively. Under 808 nm laser radiation with a photon flux of 57 mW cm-2, the homo-tandem device presents a superior PCE of 38.5%. This study provides a new ETL for constructing all-solution-processed organic/organic ICL, which can be integrated in flexible and wearable devices.

Advances in Single-Crystal Films: Synergistic Insights from Perovskites and Organic Molecules for High-Performance Optoelectronics

Semiconductor single-crystal thin films are crucial for the advancement of high-performance optoelectronic devices. Despite significant progress in fabricating perovskite and organic single-crystal films, interdisciplinary insights between these domains remain unexplored. This review aims to bridge this gap by summarizing recent advances in fabrication strategies for perovskite and organic molecular single-crystal films. Five preparation methods-solution-phase epitaxy, solid-phase epitaxy, meniscus-induced crystallization, antisolvent-induced crystallization, and space-confined growth-are analyzed with a focus on their principles, functional properties, and distinct advantages. By comparing these approaches across material systems, this review identifies transferable insights that can drive the development of large-scale, high-quality single-crystal films. Furthermore, the optoelectronic applications of these films are explored, including solar cells, photodetectors, light-emitting devices, and transistors, while addressing challenges such as scalability, defect control, and integration. This work highlights the importance of cross-disciplinary innovation and provides an effective pathway for integrating perovskite and organic molecular processing to advance the next generation of single-crystal film technologies.

Enhancing the Built-In Electric Field of Thickness-Insensitive Small Molecule Cathode Interlayers for High-Efficiency and Stable Organic Solar Cells

The built-in electric field (BEF) is proposed as a critical design parameter for optimizing small-molecule cathode interlayer materials (SM-CIMs) in organic solar cells (OSCs). By strategically transforming imidazole-functionalized triads from a donor-acceptor-donor (D-A-D) to an A-D-A configuration and replacing the A unit with a more electron-deficient moiety, we developed three triads: (TBT)2NDI, (NDI)2TBT, and (PDI)2TBT, each exhibiting progressively enhanced BEF, along with improved conductivity, work function (WF) adjustability, energy level alignment, and crystallinity. Additionally, the A-D-A triads facilitate superior electronic communication with both non-fullerene acceptors (NFAs) and polymer donors, enhancing photoexcitation utilization and reducing triplet state formation. Consequently, transitioning from (TBT)2NDI to (NDI)2TBT and then to (PDI)2TBT significantly boosts OSC efficiency and operational stability. Notably, devices with (PDI)2TBT and (NDI)2TBT retain 85.0% and 82.3% of their peak efficiencies, respectively, far exceeding the (TBT)2NDI-based device (65.9%) at an interlayer thickness of approximately 105 nm. Furthermore, (PDI)2TBT exhibits excellent compatibility with various active layers, and an outstanding performance of 20.10% is recorded in the PM6:L8-BO:BTP-eC9 system. This comprehensive study, encompassing molecular design, theoretical simulation, device fabrication, and fundamental device physics, highlights the importance of strategic donor-acceptor (D-A) electronic framework modifications to enhance BEF, thereby advancing the development of sophisticated SM-CIMs for OSCs.

Giant Near-Infrared Induced Polarization Change via a Long-Lived Hidden Phase of a Valence Tautomeric Complex

Light-induced polarization change has attracted significant attention due to its rapid response and nondestructive nature, positioning it as a promising candidate for next-generation molecular storage devices and energy harvesting. However, achieving substantial photoconversion that results in giant polarization changes via a hidden phase under near-infrared light irradiation remains a formidable challenge. In this study, we successfully synthesized a novel [CrCo] complex with an enantiopure ligand. Unlike previously reported Co valence tautomeric (VT) complexes, this complex exhibits light-induced VT (LIVT) with nearly complete photoconversion ratio upon irradiation with a 1340 nm laser. Additionally, the molecules pack in the P21 polar space group with an optimized arrangement, leading to a giant NIR-induced polarization change (1.71 μC cm-2), which surpasses that of other nonferroelectric crystals. Importantly, electric measurements and single-crystal X-ray analysis after irradiation revealed that the induced polarization change is related to not only the directional electron transfer but also the displacement of anions, which render a distinct hidden metastable phase compared to the thermally approachable one. Moreover, pyroelectric measurement was first used to characterize relaxation kinetics after light irradiation.

Efficient Infrared-Detecting Organic Semiconductors Featuring a Tetraheterocyclic Core with Reduced Ionization Potential

Infrared organic semiconductors are crucial in organic optoelectronics, yet high-performance materials with photoresponse beyond 1.1 μm (the limit of crystalline silicon) remain scarce due to the limit of building blocks including strong electron-donating units. Here, we report an asymmetric tetraheterocycle (TPCT) with a reduced ionization potential of 6.18 eV relative to those reported dithiophene-based electron-donating blocks, and TPCT-2F and TPCTO-2F constructed with TPCT as the core exhibit absorption onset up to 1 μm and 1.4 μm, respectively. Especially, TPCTO-2F possesses a narrow band gap of 1.00 eV and displays a small Urbach energy of 22.0 meV comparable to or even lower than those of some typical inorganic short-wave infrared (SWIR) semiconductors (13-44 meV). The organic photodetectors (OPDs) based on TPCT-2F achieve a peak detectivity (D*) of 2.2×1013 Jones at 810 nm under zero bias, among the highest values for reported OPDs and on par with commercial silicon photodetectors. Impressively, TPCTO-2F-based OPDs demonstrate a wide response from 0.3 to 1.4 μm and high D* comparable to germanium photodetector at wavelengths <1.2 μm with a maximum D* of 2.3×1011 Jones at 1.06 μm in SWIR region.

Electron-Rich Heptacyclic S,N Heteroacene Enabling C-Shaped A-D-A-type Electron Acceptors With Photoelectric Response beyond 1000 Nm for Highly Sensitive Near-Infrared Photodetectors

A highly electron-rich S,N heteroacene building block is developed and condensed with FIC and Cl-IC acceptors to furnish CT-F and CT-Cl, which exhibit near-infrared (NIR) absorption beyond 1000 nm. The C-shaped CT-F and CT-Cl self-assemble into a highly ordered 3D intermolecular packing network via multiple π-π interactions in the single crystal structures. The CT-F-based organic photovoltaic (OPV) achieved an impressive efficiency of 14.30% with a broad external quantum efficiency response extending from the UV-vis to the NIR (300-1050 nm) regions, outperforming most binary OPVs employing NIR A-D-A-type acceptors. CT-Cl possesses a higher surface energy than CT-F, promoting vertical phase segregation and resulting in its preferential accumulation near the bottom interface of the blend. This arrangement, combined with the lower HOMO energy level of CT-Cl, effectively reduces undesired hole and electron injection under reverse voltage. The PM6:CT-Cl-based organic photodetectors (OPDs) devices achieved an ultra-high shot-noise-limited specific detectivity (Dsh*) values exceeding 1014 Jones in the NIR region from 620 to 1000 nm, reaching an unprecedentedly high value of 1.3 × 1014 Jones at 950 nm. When utilizing a 780 nm light source, the PM6:CT-Cl-based OPDs show record-high rise/fall times of 0.33/0.11 µs and an exceptional cut-off frequency (f-3dB) of 590 kHz at -1 V.

Preparation of Dual-Asymmetric Acceptors via Selenium Substitution Combined with Terminal Group Optimization Strategy for High Efficiency Organic Solar Cells

Improving both the open-circuit voltage (VOC) and short-circuit current density (JSC) through the development of photovoltaic materials to achieve high power conversion efficiency (PCE) is critical and a significant challenge for organic solar cells (OSCs). Here, we designed novel dual-asymmetric acceptors A-SSe-TCF and A-SSe-LSF by simultaneously asymmetrically regulating the backbone and terminal groups and investigated their synergistic effects on photovoltaic performance in comparison with the monoasymmetric acceptor A-SSe-4F. The dual-asymmetric acceptors exhibit broader spectral absorption and larger half-molecule dipole moment differences, which favored the enhancement of JSC and the reduction of energy loss (Eloss). Among the binary blends, PM6:A-SSe-TCF exhibits superior phase separation, vertical phase distribution morphology, and more ordered π-π stacking compared to PM6:A-SSe-LSF and PM6:A-SSe-4F. As a result, OSCs based on PM6:A-SSe-TCF achieved a higher PCE of 18.53% with both higher VOC and JSC due to the suppressed nonradiative recombination and enhanced charge extraction capabilities. Furthermore, by incorporating A-SSe-TCF as the third component, the PM6:L8-BO:A-SSe-TCF-based device achieves a champion PCE of 19.73% without VOC loss on account of the decrement of Eloss. The novel dual-asymmetric strategy provides new insights into the molecular design and the improvement of PCE for OSCs.

Construction of Linear Tetramer-Type Acceptors for High-Efficiency and High-Stability Organic Solar Cells

Thanks to the development of non-fullerene acceptor (NFA) materials, the photovoltaic conversion efficiency (PCE) of organic solar cells (OSCs) has exceeded 20 %, which has met the requirements for commercialisation. In the current stage, the main focus is to balance the performance and stability. It has been shown that all-polymer formulation can improve device stability, however, PCE is not in satifsfaction, and the batch-to-batch variation leads to quality control issues. In this work, we constructed monodispersed tetramer NFA materials named G-1 and G-2, to best integrate the merits of small molecule and polymer. Density functional theory (DFT) calculations and experimental results showed that different connecting units at the centre could significantly affect the molecular planarity and thin film morphology. The alkene-bonded tetramer G-1 had a more regioregular structure, which leads to better molecular planarity, and more ordered packing in thin film. More importantly, the oligomeration induced a favourable face-on orientation, achieved a lower binding energy and exhibited a higher photoluminescence yield. As a result, the exciton and charge carrier kinetics was optimized with reduced non-radiative energy loss. The OSC based on PM6 : G-1 achieved a PCE of 19.6 %, which is the highest PCE reported so far for oligomer-based binary OSC. In addition, the device stability was largely improved, showing a lifetime over 10000 hours in the inverted OSC device.

Benzothiadiazole-Fused Cyanoindone: A Superior Building Block for Designing Ultra-Narrow Bandgap Electron Acceptor with Long-Range Ordered Stacking

There are great demands of developing ultra-narrow bandgap electron acceptors for multifunctional electronic devices, particularly semi-transparent organic photovoltaics (OPVs) for building-integrated applications. However, current ultra-narrow bandgap materials applied in OPVs, primarily based on electron-rich cores, exhibit defects of high-lying energy levels and inferior performance. We herein proposed a novel strategy by designing the benzothiazole-fused cyanoindone (BTC) unit with ultra-strong electron-withdrawing ability as the terminal to synthesize the acceptor BTC-2. The BTC unit imparts red-shifted absorption up to 1000 nm to BTC-2, attributed to enhanced intramolecular charge transfer and the quinoid resonance effect. Additionally, BTC-2 features deep-lying energy levels with the highest occupied molecular orbital level of -5.81 eV, due to the ultra-strong electron-withdrawing ability of BTC. Furthermore, BTC-2 exhibits long-range ordering in both molecular packing and macroscopic blend morphology, resulting from shoulder-to-shoulder packing of two BTC units, leading to an ultra-long exciton lifetime over 1.1 ns. These superiorities facilitated a 17.17 % efficiency in the binary OPV device with an extremely high photocurrent of 30.34 mA cm-2, representing the best performance for ultra-narrow bandgap electron acceptors, and a record light utilization efficiency of 4.88 % in binary semi-transparent systems. Overall, BTC is a superior building block for designing ultra-narrow bandgap electron acceptors.

Revealing Intrinsic Free Charge Generation: Promoting the Construction of Over 19% Efficient Planar p-n Heterojunction Organic Solar Cells

Due to high binding energy and extremely short diffusion distance of Frenkel excitons in common organic semiconductors at early stage, mechanism of interface charge transfer-mediated free carrier generation has dominated the development of bulk heterojunction (BHJ) organic solar cells (OSCs). However, considering the advancements in materials and device performance, it is necessary to reexamine the photoelectric conversion in current-stage efficient OSCs. Here, we propose that the conjugated materials with specific three-dimensional donor-acceptor conjugated packing potentially exhibit distinctive charge photogeneration mechanism, which spontaneously split Wannier-Mott excitons to free carriers in pure phases. Subsequently, the pure planar p-n heterojunction (PHJ) OSCs based on green orthogonal solvents were prepared and exhibited comparable even greater performance to that of BHJ OSCs. More interestingly, by introducing PVDF-TrFE as intrinsic region to regulate built-in electric field of the device, the planar p-i-n PHJ OSCs achieved much higher efficiency (>18%) and stability. Moreover, a prominent efficiency of over 19% has been obtained via ternary optimization, which is the new efficiency record for PHJ OSCs up to date. This study points towards the distinguishing intrinsic free charge generation mechanism, opens up a new avenue for OSCs to collectively realize high-efficiency, long-term duration, and simplified device engineering for future commercialization.

Radical-Triggered Bicyclization and Aryl Migration of 1,7-Diynes with Diphenyl Diselenide for the Synthesis of Selenopheno[3,4-c]quinolines

The translocation of an aryl group from selenium into carbon enabled by the cleavage of the C-Se bond is reported by using nitrogen atom-linked 1,7-diynes and diaryl diselenides as starting materials, leading to various selenophene derivatives in a regioselective manner. This method enables the construction of two C-Se bonds and two C-C bonds through sequential radical bicyclization and 1,2-aryl migration under metal-free conditions. Control experiments and mechanistic studies suggest that this reaction proceeds through the cleavage of the inert C(Ph)-Se bond, facilitating the aryl translocation process. This transformation enables the one-step conversion of simple diselenides into diverse selenopheno[3,4-c]quinolines via a radical-promoted process, holding significant potential for new seleniferous heterocycles.

Reinforcing Bulk Heterojunction Morphology through Side Chain-Engineered Pyrrolopyrrole-1,3-dione Polymeric Donors for Nonfullerene Organic Solar Cells

Organic solar cells (OSCs) are attracting significant attention due to their low cost, lightweight, and flexible nature. The introduction of nonfullerene acceptors (NFAs) has propelled OSC development into a transformative era. However, the limited availability of wide band gap polymer donors for NFAs poses a critical challenge, hindering further advancements. This study examines the role of developed wide band gap halogenated pyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (PPD)-based polymers, in combination with the Y6 nonfullerene acceptor, in bulk heterojunction (BHJ) OSCs. We first focus on the electronic and absorbance modifications brought about by halogen substitution in PPD-based polymers, revealing how these adjustments influence the HOMO/LUMO energy levels and, subsequently, photovoltaic performance. Despite the increased V oc of halogenated polymers due to the optimal band alignment, power conversion efficiencies (PCEs) were decreased due to suboptimal blend morphologies. We second implemented PPD as a solid additive to PM6:Y6, forming ternary OSCs and further improving the PCE. The study provides a nuanced understanding of the interplay between molecular design, device morphology, and OSC performance and opens insights for future research to achieve an optimal balance between band alignment and favorable blend morphology for high-efficiency OSCs.

Integrated Omnidirectional Design of Non-Volatile Solid Additive Enables Binary Organic Solar Cells with Efficiency Exceeding 19.5

Solid additives have drawn great attention due to their numerous appealing benefits in enhancing the power conversion efficiencies (PCEs) of organic solar cells (OSCs). To date, various strategies have been reported for the selection or design of non-volatile solid additives. However, the lack of a general design/evaluation principles for developing non-volatile solid additives often results in individual solid additives offering only one or two efficiency-boosting attributes. In this work, we propose an integrated omnidirectional strategy for designing non-volatile solid additives. By validating the method on the 4,5,9,10-pyrene diimide (PyDI) system, a novel non-volatile solid additive named PyMC5 was designed. PyMC5 is capable of enhancing device performance by establishing synergistic dual charge transfer channels, forming appropriate interactions with active layer materials, reducing non-radiative voltage loss and optimizing film morphology. Notably, the binary device (PM6 : L8-BO) treated by PyMC5 achieved a PCE over 19.5 %, ranking among the highest reported to date. In addition, the integration of PyMC5 mitigated the degradation process of the devices under photo- and thermal-stress conditions. This work demonstrates an efficient integrated omnidirectional approach for designing non-volatile solid additives, offering a promising avenue for further advancements in OSC development.

Unlocking high-performance near-infrared photodetection: polaron-assisted organic integer charge transfer hybrids

Room temperature femtowatt sensitivity remains a sought-after attribute, even among commercial inorganic infrared (IR) photodetectors (PDs). While organic IR PDs are poised to emerge as a pivotal sensor technology in the forthcoming Fourth-Generation Industrial Era, their performance lags behind that of their inorganic counterparts. This discrepancy primarily stems from poor external quantum efficiencies (EQE), driven by inadequate exciton dissociation (high exciton binding energy) within organic IR materials, exacerbated by pronounced non-radiative recombination at narrow bandgaps. Here, we unveil a high-performance organic Near-IR (NIR) PD via integer charge transfer between Poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (C-14PBTTT) donor (D) and Tetrafluorotetracyanoquinodimethane (TCNQF4) acceptor (A) molecules, showcasing strong low-energy subgap absorptions up to 2.5 µm. We observe that specifically, polaron excitation in these radical and neutral D-A blended molecules enables bound charges to exceed the Coulombic attraction to their counterions, leading to an elevated EQE (polaron absorption region) compared to Frenkel excitons. As a result, our devices achieve a high EQE of ∼107%, femtowatt sensitivity (NEP) of ~0.12 fW Hz-1/2 along a response time of ~81 ms, at room temperature for a wavelength of 1.0 µm. Our innovative utilization of polarons highlights their potential as alternatives to Frenkel excitons in high-performance organic IR PDs.

Highly efficient organic solar cells enabled by suppressing triplet exciton formation and non-radiative recombination

The high non-radiative energy loss is a bottleneck issue that impedes the improvement of organic solar cells. The formation of triplet exciton is thought to be the main source of the large non-radiative energy loss. Decreasing the rate of back charge transfer is considered as an effective approach to alleviate the relaxation of the charge-transfer state and the triplet exciton generation. Herein, we develops an efficient ternary system based on D18:N3-BO:F-BTA3 by regulating the charge-transfer state disorder and the rate of back charge transfer of the blend. With the addition of F-BTA3, a well-defined morphology with a more condensed molecular packing is obtained. Moreover, a reduced charge-transfer state disorder is demonstrated in the ternary blend, which decreases the rate of back charge transfer as well as the triplet exciton formation, and therefore hinders the non-radiative recombination pathways. Consequently, D18:N3-BO:F-BTA3-based device produces a low non-radiative energy loss of 0.183 eV and a record-high efficiency of 20.25%. This work not only points towards the significant role of the charge-transfer state disorder on the suppression of triplet exciton formation and the non-radiative energy loss, but also provides a valuable insight for enhancing the performance of OSCs.

Achieving High Efficiency and Stability in Organic Photovoltaics with a Nanometer-Scale Twin p-i-n Structured Active Layer

In pursuing high stability and power conversion efficiency for organic photovoltaics (OPVs), a sequential deposition (SD) approach to fabricate active layers with p-i-n structures (where p, i, and n represent the electron donor, mixed donor:acceptor, and electron acceptor regions, respectively, distinctively different from the bulk heterojunction (BHJ) structure) has emerged. Here, we present a novel approach that by incorporating two polymer donors, PBDBT-DTBT and PTQ-2F, and one small-molecule acceptor, BTP-3-EH-4Cl, into the active layer with sequential deposition, we formed a device with nanometer-scale twin p-i-n structured active layer. The twin p-i-n PBDBT-DTBT:PTQ-2F/BTP-3-EH-4Cl device involved first depositing a PBDBT-DTBT:PTQ-2F blend under layer and then a BTP-3-EH-4Cl top layer and exhibited an improved power conversion efficiency (PCE) value of 18.6%, as compared to the 16.4% for the control BHJ PBDBT-DTBT:PTQ-2F:BTP-3-EH-4Cl device or 16.6% for the single p-i-n PBDBT-DTBT/BTP-3-EH-4Cl device. The PCE enhancement resulted mainly from the twin p-i-n active layer's multiple nanoscale charge carrier pathways that contributed to an improved fill factor and faster photocurrent generation based on transient absorption studies. The PBDBT-DTBT:PTQ-2F/BTP-3-EH-4Cl film possessed a vertical twin p-i-n morphology that was revealed through secondary ion mass spectrometry and synchrotron grazing-incidence small-angle X-ray scattering analyses. The thermal stability (T80) at 85 °C of the twin p-i-n PBDBT-DTBT:PTQ-2F/BTP-3-EH-4Cl device surpassed that of the single p-i-n PBDBT-DTBT/BTP-3-EH-4Cl devices (906 vs 196 h). This approach of providing a twin p-i-n structure in the active layer can lead to substantial enhancements in both the PCE and stability of organic photovoltaics, laying a solid foundation for future commercialization of the organic photovoltaics technology.

Halogenated Dibenzo[f,h]quinoxaline Units Constructed 2D-Conjugated Guest Acceptors for 19% Efficiency Organic Solar Cells

Halogenation of Y-series small-molecule acceptors (Y-SMAs) is identified as an effective strategy to optimize photoelectric properties for achieving improved power-conversion-efficiencies (PCEs) in binary organic solar cells (OSCs). However, the effect of different halogenation in the 2D-structured large π-fused core of guest Y-SMAs on ternary OSCs has not yet been systematically studied. Herein, four 2D-conjugated Y-SMAs (X-QTP-4F, including halogen-free H-QTP-4F, chlorinated Cl-QTP-4F, brominated Br-QTP-4F, and iodinated I-QTP-4F) by attaching different halogens into 2D-conjugation extended dibenzo[f,h]quinoxaline core are developed. Among these X-QTP-4F, Cl-QTP-4F has a higher absorption coefficient, optimized molecular crystallinity and packing, suitable cascade energy levels, and complementary absorption with PM6:L8-BO host. Moreover, among ternary PM6:L8-BO:X-QTP-4F blends, PM6:L8-BO:Cl-QTP-4F obtains a more uniform and size-suitable fibrillary network morphology, improved molecular crystallinity and packing, as well as optimized vertical phase distribution, thus boosting charge generation, transport, extraction, and suppressing energy loss of OSCs. Consequently, the PM6:L8-BO:Cl-QTP-4F-based OSCs achieve a 19.0% efficiency, which is among the state-of-the-art OSCs based on 2D-conjugated Y-SMAs and superior to these devices based on PM6:L8-BO host (17.70%) and with guests of H-QTP-4F (18.23%), Br-QTP-4F (18.39%), and I-QTP-4F (17.62%). The work indicates that halogenation in 2D-structured dibenzo[f,h]quinoxaline core of Y-SMAs guests is a promising strategy to gain efficient ternary OSCs.

Highly Efficient and Stable Organic Photovoltaic Cells for Underwater Applications

Organic photovoltaic (OPV) technology holds tremendous promise as a sustainable power source for underwater off-grid systems. However, research on underwater OPV cells is relatively scarce. Here, this gap is addressed by focusing on the exploration and development of OPV cells specifically designed for underwater applications. An acceptor, named ITO-4Cl, with excellent water resistance, is rationally designed and synthesized. Benefiting from its low energetic disorder and an absorption spectrum well-suited to the underwater environment, the ITO-4Cl-based OPV cell achieves an unprecedented power conversion efficiency (PCE) of over 25.6% at a water depth of 1 m. Additionally, under 660 nm laser irradiation, the cell demonstrates a notable PCE of 31.6%, indicating its potential for underwater wireless energy transfer. Due to the mitigation of thermal effects from solar irradiation, the lifetime of the ITO-4Cl-based OPV cell exceeds 7000 h. Additionally, a flexible OPV cell is fabricated that maintains its initial PCE even under exposure to high pressures of 5 MPa. A 32.5 cm2 flexible module achieves an excellent PCE of 17%. This work fosters a deeper understanding of underwater OPV cells and highlights the promising prospects of OPV cells for underwater applications.

Ethylenedioxythiophene-Based Small Molecular Donor with Multiple Conformation Locks for Organic Solar Cells with Efficiency of 19.3

Ternary organic solar cells (T-OSCs) represent an efficient strategy for enhancing the performance of OSCs. Presently, the majority of high-performance T-OSCs incorporates well-established Y-acceptors or donor polymers as the third component. In this study, a novel class of conjugated small molecules has been introduced as the third component, demonstrating exceptional photovoltaic performance in T-OSCs. This innovative molecule comprises ethylenedioxythiophene (EDOT) bridge and 3-ethylrhodanine as the end group, with the EDOT unit facilitating the creation of multiple conformation locks. Consequently, the EDOT-based molecule exhibits two-dimensional charge transport, distinguishing it from the thiophene-bridged small molecule, which displays fewer conformation locks and provides one-dimensional charge transport. Furthermore, the robust electron-donating nature of EDOT imparts the small molecule with cascade energy levels relative to the electron donor and acceptor. As a result, OSCs incorporating the EDOT-based small molecule as the third component demonstrate enhanced mobilities, yielding a remarkable efficiency of 19.3 %, surpassing the efficiency of 18.7 % observed for OSCs incorporating thiophene-based small molecule as the third component. The investigations in this study underscore the excellence of EDOT as a building block for constructing conjugated materials with multiple conformation locks and high charge carrier mobilities, thereby contributing to elevated photovoltaic performance in OSCs.

Efficient and stable hybrid perovskite-organic light-emitting diodes with external quantum efficiency exceeding 40 per cent

Light-emitting diodes (LEDs) based on perovskite semiconductor materials with tunable emission wavelength in visible light range as well as narrow linewidth are potential competitors among current light-emitting display technologies, but still suffer from severe instability driven by electric field. Here, we develop a stable, efficient and high-color purity hybrid LED with a tandem structure by combining the perovskite LED and the commercial organic LED technologies to accelerate the practical application of perovskites. Perovskite LED and organic LED with close photoluminescence peak are selected to maximize photon emission without photon reabsorption and to achieve the narrowed emission spectra. By designing an efficient interconnecting layer with p-type interface doping that provides good opto-electric coupling and reduces Joule heating, the resulting green emitting hybrid LED shows a narrow linewidth of around 30 nm, a peak luminance of over 176,000 cd m-2, a maximum external quantum efficiency of over 40%, and an operational half-lifetime of over 42,000 h.

Metalla-Carbaporphyrinoids Consisting of an Acyclic N-Confused Tetrapyrrole Analogue Served as Stable Near-Infrared-II Dyes

We present herein the synthesis of novel pseudo-metalla-carbaporphyrinoid species (1M: M=Pd and Pt) achieved through the inner coordination of palladium(II) and platinum(II) with an acyclic N-confused tetrapyrrin analogue. Despite their tetrapyrrole frameworks being small, akin to well-known porphyrins, these species exhibit an unusually narrow HOMO-LUMO gap, resulting in an unprecedentedly low-energy absorption in the second near-infrared (NIR-II) region. Density functional theory (DFT) calculations revealed unique dπ-pπ-conjugated electronic structures involving the metal dπ-ligand pπ hybridized molecular orbitals of 1M. Magnetic circular dichroism (MCD) spectroscopy confirmed distinct electronic structures. Remarkably, the complexes feature an open-metal coordination site in the peripheral NN dipyrrin site, forming hetero-metal complexes (1Pd-BF2 and 1Pt-BF2) through boron difluoride complexation. The resulting hetero metalla-carbaporphyrinoid species displayed further redshifted NIR-II absorption, highly efficient photothermal conversion efficiencies (η; 62-65 %), and exceptional photostability. Despite the challenges associated with the theoretical and experimental assessment of dπ-pπ-conjugated metalla-aromaticity in relatively larger (more than 18π electrons) polycyclic ring systems, these organometallic planar tetrapyrrole systems could serve as potential molecular platforms for aromaticity-relevant NIR-II dyes.

Exploring structure-property landscape of non-fullerene acceptors for organic solar cells

We present a comprehensive analysis of the structure-property relationship in small molecule non-fullerene acceptors (NFAs) featuring an acceptor-donor-acceptor configuration employing state-of-the-art quantum chemical computational methods. Our focus lies in the strategic functionalization of halogen groups at the terminal positions of NFAs as an effective means to mitigate non-radiative voltage losses and augment photovoltaic and photophysical properties relevant to organic solar cells. Through photophysical studies, we observe a bathochromic shift in the visible region for all halogen-functionalized NFAs, except type-2, compared to the unmodified compound. Most of these functionalized compounds exhibit exciton binding energies below 0.3 eV and ΔLUMO less than 0.3 eV, indicating their potential as promising candidates for organic solar cells. Selected candidate structures undergo an analysis of charge transport properties using the semi-classical Marcus theory based on hopping transport formalism. Molecular dynamics simulations followed by charge transport simulations reveal an ambipolar nature of charge transport in the investigated NFAs, with equivalent hole and electron mobilities compared to the parent compound. Our findings underscore the crucial role of end-group functionalization in enhancing the photovoltaic and photophysical characteristics of NFAs, ultimately improving the overall performance of organic solar cells. This study advances our understanding of the structure-property relationships in NFAs and provides valuable insights into the design and optimization of organic solar cell materials.

Pyrrole-Based Fully Non-fused Acceptor for Efficient and Stable Organic Solar Cells

Organic solar cells (OSCs) are still suffering from the low light utilization and unstable under ultraviolet irradiation. To tackle these challenges, we design and synthesize a non-fused acceptor based on 1-(2-butyloctyl)-1H-pyrrole as π-bridge unit, denoted as GS70, which serves as active layer in the front-cell for constructing tandem OSCs with a parallel configuration. Benefiting from the well-complementary absorption spectra with the rear-cell, GS70-based parallel tandem OSCs exhibit an improved photoelectron response over the range between 600-700 nm, yielding a high short-circuit current density of 28.4 mA cm-2. The improvement in light utilization translates to a power conversion efficiency of 19.4 %, the highest value among all parallel tandem OSCs. Notably, owing to the intrinsic stability of GS70, the manufactured parallel tandem OSCs retain 84.9 % of their initial PCE after continuous illumination for 1000 hours. Overall, this work offers novel insight into the molecular design of low-cost and stability non-fused acceptors, emphasizing the importance of adopting a parallel tandem configuration for achieving efficient light harvesting and improved photostability in OSCs.

Resolving electron and hole transport properties in semiconductor materials by constant light-induced magneto transport

The knowledge of minority and majority charge carrier properties enables controlling the performance of solar cells, transistors, detectors, sensors, and LEDs. Here, we developed the constant light induced magneto transport method which resolves electron and hole mobility, lifetime, diffusion coefficient and length, and quasi-Fermi level splitting. We demonstrate the implication of the constant light induced magneto transport for silicon and metal halide perovskite films. We resolve the transport properties of electrons and holes predicting the material's effectiveness for solar cell application without making the full device. The accessibility of fourteen material parameters paves the way for in-depth exploration of causal mechanisms limiting the efficiency and functionality of material structures. To demonstrate broad applicability, we further characterized twelve materials with drift mobilities spanning from 10-3 to 103 cm2V-1s-1 and lifetimes varying between 10-9 and 10-3 seconds. The universality of our method its potential to advance optoelectronic devices in various technological fields.

Achieving Desired Pseudo-Planar Heterojunction Organic Solar Cells via Binary-Dilution Strategy

The sequential deposition process has demonstrated the great possibility to achieve a photolayer architecture with an ideal gradient phase separation morphology, which has a vital influence on the physical processes that determine the performance of organic solar cells (OSCs). However, the controllable preparation of pseudo-planar heterojunction (P-PHJ) with gradient distribution has not been effectively elucidated. Herein, a binary-dilution strategy is proposed, the PM6 solution with micro acceptor BO-4Cl and the L8-BO solution with micro donor PM6 respectively, to form P-PHJ film. This architecture exists good donor (D) and acceptor (A) vertical gradient distribution and larger D/A interpenetrating regions, which promotes exciton generation and dissociation, shortens charge transport distance and optimizes carrier dynamics. Moreover, the dilution of PM6 by BO-4Cl promotes the regulation of active layer aggregation size and phase purity, thus alleviating energy disorder and voltage loss. As a result, the P-PHJ device exhibits an outstanding power conversion efficiency of 19.32% with an excellent short-circuit current density of 26.92 mA cm-2 , much higher than planar binary heterojunction (17.67%) and ternary bulk heterojunction (18.49%) devices. This research proves a simple but effective method to provide an avenue for constructing desirable active layer morphology and high-performance OSCs.

Stereoisomeric Non-Fullerene Acceptors-Based Organic Solar Cells

Chiral alkyl chains are ubiquitously observed in organic semiconductor materials and can regulate solution processability and active layer morphology, but the effect of stereoisomers on photovoltaic performance has rarely been investigated. For the racemic Y-type acceptors widely used in organic solar cells, it remains unknown if the individual chiral molecules separate into the conglomerate phase or if racemic phase prevails. Here, the photovoltaic performance of enantiomerically pure Y6 derivatives, (S,S)/(R,R)-BTP-4F, and their chiral mixtures are compared. It is found that (S,S) and (R,R)-BTP-4F molecule in the racemic mixtures tends to interact with its enantiomer. The racemic mixtures enable efficient light harvesting, fast hole transfer, and long polaron lifetime, which is conducive to charge generation and suppresses the recombination losses. Moreover, abundant charge diffusion pathways provided by the racemate contribute to efficient charge transport. As a result, the racemate system maximizes the power output and minimizes losses, leading to a higher efficiency of 18.16% and a reduced energy loss of 0.549 eV, as compared to the enantiomerically pure molecules. This study demonstrates that the chirality of non-fullerene acceptors should receive more attention and be designed rationally to enhance the efficiency of organic solar cells.

Optimized Crystal Framework by Asymmetric Core Isomerization in Selenium-Substituted Acceptor for Efficient Binary Organic Solar Cells

Both the regional isomerization and selenium-substitution of the small molecular acceptors (SMAs) play significant roles in developing efficient organic solar cells (OSCs), while their synergistic effects remain elusive. Herein, we developed three isomeric SMAs (S-CSeF, A-ISeF, and A-OSeF) via subtly manipulating the mono-selenium substituted position (central, inner, or outer) and type of heteroaromatic ring on the central core by synergistic strategies for efficient OSCs, respectively. Crystallography of asymmetric A-OSeF presents a closer intermolecular π-π stacking and more ordered 3-dimensional network packing and efficient charge-hopping pathways. With the successive out-shift of the mono-selenium substituted position, the neat films give a slightly wider band gap and gradually higher crystallinity and electron mobility. The PM1 : A-OSeF afford favourable fibrous phase separation morphology with more ordered molecular packing and efficient charge transportation compared to the other two counterparts. Consequently, the A-OSeF-based devices achieve a champion efficiency of 18.5 %, which represents the record value for the reported selenium-containing SMAs in binary OSCs. Our developed precise molecular engineering of the position and type of selenium-based heteroaromatic ring of SMAs provides a promising synergistic approach to optimizing crystal stacking and boosting top-ranked selenium-containing SMAs-based OSCs.

Correlation of Broad Absorption Band with Small Singlet-Triplet Energy Gap in Organic Photovoltaics

Organic photovoltaics (OPV) are one of the most effective ways to harvest renewable solar energy, with the power conversion efficiency (PCE) of the devices soaring above 19 % when processed with halogenated solvents. The superior photocurrent of OPV over other emerging photovoltaics offers more opportunities to further improve the efficiency. Tailoring the absorption band of photoactive materials is an effective way to further enhance OPV photocurrent. However, the field has mostly been focusing on improving the near-infrared region photo-response, with the absorption shoulders in short-wavelength region (SWR) usually being neglected. Herein, by developing a series of non-fullerene acceptors (NFAs) with varied side-group conjugations, we observe an enhanced SWR absorption band with increased side-group conjugation length. The underpinning factors of how molecular structures and geometries improve SWR absorption are clearly elucidated through theoretical modelling and crystallography. Moreover, a clear relationship between the enhanced SWR absorption and reduced singlet-triplet energy gap is established, both of which are favorable for the OPV performance and can be tailored by rational structure design of NFAs. Finally, the rationally designed NFA, BO-TTBr, affords a decent PCE of 18.5 % when processed with a non-halogenated green solvent.

Progress and Challenges Toward Effective Flexible Perovskite Solar Cells

The demand for building-integrated photovoltaics and portable energy systems based on flexible photovoltaic technology such as perovskite embedded with exceptional flexibility and a superior power-to-mass ratio is enormous. The photoactive layer, i.e., the perovskite thin film, as a critical component of flexible perovskite solar cells (F-PSCs), still faces long-term stability issues when deformation occurs due to encountering temperature changes that also affect intrinsic rigidity. This literature investigation summarizes the main factors responsible for the rapid destruction of F-PSCs. We focus on long-term mechanical stability of F-PSCs together with the recent research protocols for improving this performance. Furthermore, we specify the progress in F-PSCs concerning precise design strategies of the functional layer to enhance the flexural endurance of perovskite films, such as internal stress engineering, grain boundary modification, self-healing strategy, and crystallization regulation. The existing challenges of oxygen-moisture stability and advanced encapsulation technologies of F-PSCs are also discussed. As concluding remarks, we propose our viewpoints on the large-scale commercial application of F-PSCs.

Theoretical investigation on the functional group modulation of UV-Vis absorption profiles of triphenylamine derivatives

Understanding the functional group modulation of electronic structure and excitation is pivotal to the design of organic small molecules (OSMs) for photoelectric applications. In this study, we employed density functional theory (DFT) and time-dependent DFT (TDDFT) calculations to explore the unique absorption character of four triphenylamine photosensitizers. The various conformations were investigated given the multiple single bonds in the compounds, and the resemblance in the electronic structure of different conformations is affirmed because the coplanarity and consequent long-range conjugation is maintained regardless of the orientation of the flexible blocks. Six functionals were evaluated, and MN15 was found to successfully reproduce the intense secondary absorption peak for the double 3,4-ethylenedioxythiophene (EDOT) modified sensitizer over B3LYP, PBE0, M062X, CAM-B3LYP, and ωB97XD. The introduction of EDOT gives rise to a new excited state S4, which is a local excitation constrained in the EDOT substituent triphenylamine block. This new excited state S4, in combination with inherent S2 and S3 derived from prototype molecule TPA-Pyc, jointly contributes to the hump of the secondary absorption peak of ETE-Pyc and finally affects the light-harvesting ability of the dye-sensitized TiO2 photoanode. The current findings provide guidance toward the rational design of OSMs with good light-harvest ability.

All-Polymer Solar Cells Sequentially Solution Processed from Hydrocarbon Solvent with a Thick Active Layer

Organic solar cells (OSCs) have gained increasing attention. Among the various directions in OSCs, all-polymer solar cells (all-PSCs) have emerged as a highly promising and currently active research area due to their excellent film formation properties, mechanical properties, and thermal stabilities. However, most of the high-efficiency all-PSCs are processed from chloroform with an active layer thickness of ~100 nm. In order to meet the requirements for industrialization, a thicker active layer processed from low-vapor pressure solvents (preferentially a hydrocarbon solvent) is strongly desired. Herein, we employ toluene (a hydrocarbon solvent with a much higher boiling point than chloroform) and a method known as sequential processing (SqP) to mitigate the rapid decline in efficiency with increasing film thickness. We show that SqP enables a more favorable vertical phase segregation that leads to less trap-assisted recombination and enhanced charge extraction and lifetime than blend-cast devices at higher film thicknesses.