Regulating the Sequence Structure of Conjugated Block Copolymers Enables Large-Area Single-Component Organic Solar Cells with High Efficiency and Stability

Organosilica Nanodots Doped ZnO Cathode Interface Layer for Highly Efficient and Stable Inverted Polymer Solar Cells

Interfacial engineering is essential to achieve optical efficiencies and facilitate the industrialization of organic solar cells (OSCs). By doping organosilica nanodots (OSiNDs) into zinc oxide (ZnO), we have developed a hybrid ZnO/OSiNDs (4 wt %) cathode interface layer (CIL) that significantly enhances the overall performance of inverted organic solar cells (i-OSCs). In the PM6/BTP-eC9 active layer system, i-OSC devices with a ZnO/OSiNDs (4 wt %) CIL exhibit a superior power conversion efficiency (PCE) of 17.49%, surpassing that of reference devices with a pure ZnO CIL (15.88%). The OSiNDs not only modulate the work function of ZnO, thereby facilitating the carrier transport between ZnO interface and active layer, but also enhance device stability. After exposure to 1200 min of 100 mW/cm2 illumination, including UV light, the devices retain 89.4% of their initial PCE, whereas devices based solely on ZnO retain only 57.7% under identical conditions. In this study, we present pioneering insights into the selection of environmentally friendly and cost-effective OSiNDs for modifying ZnO to create organic-inorganic hybrid coordination complexes as effective CILs.

Enhanced Intramolecular Hole Transfer in Block Copolymer Enables >15% and Operational Stable Single-Material-Organic Solar Cells

Recent studies on narrow bandgap all-conjugated block copolymer (BCP) single-material-organic solar cells (SMOSCs) have made unprecedented progress in power conversion efficiency (PCE); however, it still lacks understanding of the structure-property relationship in these highly mixed materials. Herein, the impact of different synthetic protocols (direct synthesis (d-BCP) versus sequential synthesis (s-BCP)) is first investigated on the relevant photovoltaic properties. Targeting the same BCP, namely PBDB-T-b-PYIT, it is found that the change in polymerization reaction leads to quite different optical and transport properties. The d-BCP outputs a record-high PCE of 15.02% for SMOSCs as well as enhanced operation stability under simulated 1-sun illumination, which is significantly higher than that of s-BCP (10.33%) and even close to its bulk heterojunction (BHJ) counterparts. Detailed transient absorption spectroscopy reveals ultrafast dynamics of charge transfer (CT) and exciton dissociation in BCP. In together with morphology characterization, it is revealed that the d-BCP has more phase pure composition, enhanced molecular ordering, and higher intramolecular CT efficiency relative to those of s-BCP. These findings gain insight into both the structure and carrier dynamic of BCP and demonstrate the possibility of achieving high-efficiency and stable SMOSCs.

Molecular Design of Active Layer for High-Performance Stretchable Organic Solar Cells

Stretchable organic solar cells (SOSCs) have advanced rapidly in the last few years as power sources required to realize portable and wearable electronics become available. Through rational material and device engineering, SOSCs are now able to retain their photovoltaic performance even when subjected to repeated mechanical deformations. However, reconciling a high efficiency and an excellent stretchability is still a huge challenge, and the development of SOSCs has lagged far behind that of flexible OSCs. In this perspective article, recent strategies for imparting mechanical robustness to SOSCs while maintaining high power conversion efficiency are reviewed, with emphasis on the molecular design of active layers. Initially, an overview of molecular design approaches and recent research advances is provided in improving the stretchability of active layers, including donors, acceptors, and single-component materials. Subsequently, another common strategy for regulating photovoltaic and mechanical properties of SOSCs, namely multi-component system, is summarized and analyzed. Lastly, considering that SOSCs research is in its infancy, the current challenges and future directions are pointed out.

Non-Fused Star-Shape Giant Trimer Electron Acceptors for Organic Solar Cells with Efficiency over 19

Organic solar cells (OSCs) based on giant molecular acceptors (GMAs) have attracted extensive attention due to their excellent power conversion efficiency (PCE) and operation stability. However, the large conjugated plane of GMAs poses great challenges in regulating the solubility, over-size aggregation and yield, which in turn further constrains their development in commercial products. Herein, we employ a non-fused skeleton strategy to develop novel non-fused star-shape trimers (3BTT6F and 3BTT6Cl) for improving device performance. Single-bond linkage can break the rigid planarity to form a 3D architecture, generating multidimensional charge transfer pathways. Importantly, the non-fused skeleton strategy can not only significantly improve solubility and synthesis yield, but also effectively suppress molecular excessive aggregation. Consequently, due to the optimized film-forming process and charge dynamics, 3BTT6F-based binary device obtains a high PCE of 17.52 %, which is significantly higher than the reported fully fused trimers. Excitingly, 3BTT6F-based ternary device even obtains a top-level PCE of 19.26 %. Furthermore, the non-fused star-shape configuration also endows these acceptors with enhanced intermolecular interaction in the active layer, demonstrating excellent operational stability. Our work emphasizes the potential of non-fused star-shape trimers, providing a new pathway for achieving highly efficient and stable OSCs.

Single-Component Organic Solar Cells with over 14% Efficiency

Single-component organic solar cells (SCOSCs), with covalently linked donor and acceptor, attract considerable attention for their improved thermodynamic stability over traditional bulk heterojunction (BHJ) organic solar cells. Despite the significant potential of SCOSCs, their efficiency has consistently trailed behind that of their BHJ counterparts for years, primarily due to challenges including rapid charge recombination, intricate phase separation, and substantial energy loss. Herein, this work represents a significant milestone in the advancement of SCOSCs based on a single component of PBDB-T-b-PYT, achieving both high efficiency (14.64%) and low energy loss (0.563 eV) through the combined use of thermal and solvent annealing. Optimized devices exhibit not only higher charge carrier mobilities but also a more balanced distribution, facilitating efficient transport and collection of photogenerated charge carriers by individual electrodes, while also demonstrating lower nonradiative recombination losses, thus contributing to superior optoelectronic performance and stability.

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.

Understanding photochemical degradation mechanisms in photoactive layer materials for organic solar cells

Over the past decades, the field of organic solar cells (OSCs) has witnessed a significant evolution in materials chemistry, which has resulted in a remarkable enhancement of device performance, achieving efficiencies of over 19%. The photoactive layer materials in OSCs play a crucial role in light absorption, charge generation, transport and stability. To facilitate the scale-up of OSCs, it is imperative to address the photostability of these electron acceptor and donor materials, as their photochemical degradation process remains a challenge during the photo-to-electric conversion. In this review, we present an overview of the development of electron acceptor and donor materials, emphasizing the crucial aspects of their chemical stability behavior that are linked to the photostability of OSCs. Throughout each section, we highlight the photochemical degradation pathways for electron acceptor and donor materials, and their link to device degradation. We also discuss the existing interdisciplinary challenges and obstacles that impede the development of photostable materials. Finally, we offer insights into strategies aimed at enhancing photochemical stability and discuss future directions for developing photostable photo-active layers, facilitating the commercialization of OSCs.

Three-in-One Strategy Enables Single-Component Organic Solar Cells with Record Efficiency and High Stability

Single-component organic solar cells (SCOSCs) with covalently bonding donor and acceptor are becoming increasingly attractive because of their superior stability over traditional multicomponent blend organic solar cells (OSCs). Nevertheless, the efficiency of SCOSCs is far behind the state-of-the-art multicomponent OSCs. Herein, by combination of the advantages of three-component and single-component devices, this work reports an innovative three-in-one strategy to boost the performance of SCOSCs. In this three-in-one strategy, three independent components (PM6, D18, and PYIT) are covalently linked together to create a new single-component active layer based on ternary conjugated block copolymer (TCBC) PM6-D18-b-PYIT by a facile polymerization. Precisely manipulating the component ratios in the polymer chains of PM6-D18-b-PYIT is able to broaden light utilization, promote charge dynamics, optimize, and stabilize film morphology, contributing to the simultaneously enhanced efficiency and stability of the SCOSCs. Ultimately, the PM6-D18-b-PYIT-based device exhibits a power conversion efficiency (PCE) of 14.89%, which is the highest efficiency of the reported SCOSCs. Thanks to the aggregation restriction of each component and chain entanglement in the three-in-one system, the PM6-D18-b-PYIT-based SCOSC displays significantly higher stability than the corresponding two-component (PM6-D18:PYIT) and three-component (PM6:D18:PYIT). These results demonstrate that the three-in-one strategy is facile and promising for developing SCOSCs with superior efficiency and stability.

Construction of Layer-Blocked Covalent Organic Framework Heterogenous Films via Surface-Initiated Polycondensations with Strongly Enhanced Photocatalytic Properties

Imine-linked covalent organic frameworks (COFs) usually show high crystallinity and porosity, while vinyl-linked COFs have excellent semiconducting properties and stability. Therefore, achieving the advantages of imine- and vinyl-linkages in a single COF material is highly interesting but remains challenging. Herein, we demonstrate the fabrication of a layer-blocked COF (LB-COF) heterogeneous film that is composed of imine- and vinyl-linkages through two successive surface-initiated polycondensations. In brief, the bottom layer of imine-linked COF film was constructed on an amino-functionalized substrate via Schiff-base polycondensation, in which the unreacted aldehyde edges could be utilized for initiating aldol polycondensation to prepare the second layer of vinyl-linked COF film. The resultant LB-COF film displays excellent ordering due to the crystalline templating effect from the bottom imine-linked COF layer; meanwhile, the upper vinyl-linked COF layer could strongly enhance its stability and photocatalytic properties. The LB COF also presents superior performance in photocatalytic uranium extraction (320 mg g-1), which is higher than the imine-linked (35 mg g-1) and the vinyl-linked (295 mg g-1) counterpart. This study provides a novel surface-initiated strategy to synthesize layer-blocked COF heterogeneous films that combine the advantages of each building block.

Single-component organic solar cells-Perspective on the importance of chemical precision in conjugated block copolymers

Organic photovoltaics (OPV) present a promising thin-film solar cell technology with particular benefits in terms of weight, aesthetics, transparency, and cost. However, despite being studied intensively since the mid 90's, OPV has not entered the mass consumer market yet. Although the efficiency gap with other thin-film photovoltaics has largely been overcome, active layer stability and performance reproducibility issues have not been fully resolved. State-of-the-art OPV devices employ a physical mixture of electron donor and acceptor molecules in a bulk heterojunction active layer. These blends are prone to morphological changes, leading to performance losses over time. On the other hand, in "single-component" organic solar cells, the donor and acceptor constituents are chemically connected within a single material, preventing demixing and thereby enhancing device stability. Novel single-component materials affording reasonably high solar cell efficiencies and improved lifetimes have recently emerged. In particular, the combination of donor and acceptor structures in conjugated block copolymers (CBCs) presents an exciting approach. Nevertheless, the current CBCs are poorly defined from a structural point of view, while synthetic protocols remain unoptimized. More controlled synthesis followed by proper structural analysis of CBCs is, however, essential to develop rational structure-property-device relations and to drive the field forward. In this perspective, we provide a short overview of the state-of-the-art in single-component organic solar cells prepared from CBCs, reflect on their troublesome characterization and the importance of chemical precision in these structures, give some recommendations, and discuss the potential impact of these aspects on the field.