Desirable Uniformity and Reproducibility of Electron Transport in Single-Component Organic Solar Cells

High-Performance Intrinsically-Stretchable Organic Solar Cells Enabled by Electron Acceptors with Flexible Linkers

Intrinsically stretchable organic solar cells (IS-OSCs) are emerging as promising candidates for powering next-generation wearable electronics. However, developing molecular design strategies to achieve both high efficiency and mechanical robustness in IS-OSCs remains a significant challenge. In this work, we present a novel approach by synthesizing a dimerized electron acceptor (DY-FBrL) that enables rigid OSCs with a high power conversion efficiency (PCE) of 18.75 % and a crack-onset strain (COS) of 18.54 %. The enhanced PCE and stretchability of DY-FBrL-based devices are attributed to its extended π-conjugated backbone and elongated side chains. Furthermore, we introduce an innovative polymerized acceptor (PDY-FL), synthesized via the polymerization of DY-FBrL. While PDY-FL-based devices exhibit a slightly lower PCE of 14.13 %, they achieve a significantly higher COS of 23.45 %, representing one of the highest PCEs reported for polymerized acceptors containing only flexible linkers. Consequently, IS-OSCs fabricated using DY-FBrL and PDY-FL achieve notable PCEs of 14.31 % and 11.61 %, respectively. Additionally, the device stretchability improves progressively from Y6 (strain at PCE80%=11 %), to DY-FBrL (strain at PCE80%=23 %), and PDY-FL (strain at PCE80%=31 %). This study presents a promising molecular design strategy for tailoring electron acceptor structures, offering a new pathway to develop high-performance IS-OSCs with enhanced mechanical properties.

α-ZnO Manipulated Growth of Ag Gird on AgNWs Enables High Conductive Flexible Electrode for Large-Area Monolithic Organic Photovoltaics

The conductivity of AgNWs electrodes can be enhanced by incorporating Ag grids, thereby facilitating the development of large-area flexible organic solar cells (FOSCs). Ag grids from vacuum evaporation offer the advantages of simple film formation, adjustable thickness, and unique structure. However, the complex 3D multi-component structure of AgNWs electrodes will exacerbate the aggregation of large Ag particles, causing the device short circuits. To address this issue, the relationship between the surface energy of modification layers and the morphology and conductivity of ultrathin Ag on AgNWs is studied. The amorphous ZnO (α-ZnO) layer promotes Ag growth from Volmer-Weber (VW) to Frank-Van der Merwe (FM), reducing particle aggregation. The 1 µm thick PET/AgNWs/Ag grid electrode with α-ZnO exhibited low contact resistance and high conductivity. As a result, 1 cm2 FOSCs with Ag grids achieve a power conversion efficiency (PCE) of 16.01%. As the area increased to 4 and 9 cm2, the performance of the monolithic FOSCs is 14.70% and 12.69%, showing less efficiency loss during upscaling. The 8 and 16 cm2 modules constructed by series and parallel connection of the monolithic devices yield PCEs of 14.47% and 12.92%, respectively. This study offers valuable insights into constructing Ag grids on AgNWs electrodes for highly efficient large-area FOSCs.

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.

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.

In-depth theoretical analysis of the influence of an external electric field on charge transport parameters

It is important to develop materials with environmental stability and long device shelf life for use in organic field-effect transistors (OFETs). The microscopic, molecular-level nature of the organic layer in OFETs is not yet well understood. The stability of geometric and electronic structures and the regulation of the external electric field (EEF) on the charge transport properties of four typical homogeneous organic semiconductors (OSCs) were investigated by density functional theory (DFT). The results showed that under the EEF, the structural changes in single-bond linked oligomers were more sensitive and complex than those of condensed molecules, and there were non-monotonic changes in their reorganization energy (λ) during charge transport under an EEF consisting of decreases and then increases (Series D). The change in λ under an EEF can be preliminarily and qualitatively determined by the change in the frontier molecular orbitals (FMOs) - the number of C-atoms with nonbonding characteristics. For single-bonded molecules, the transfer integral is basically unchanged under a low EEF, but it will greatly change at a high EEF. Because the structure and properties of the molecule will greatly change under different EEFs, the effect of an EEF should be fully considered when determining the intrinsic mobility of OSCs, which could cause a deviation 0.3-20 times in mobility. According to detailed calculations, one heterogeneous oligomer, TH-BTz, was designed. Its λ can be greatly reduced under an EEF, and the change in the energy level of FMOs can be adjusted to different degrees. This study provides a reasonable idea for verification of the experimental mobility value and also provides guidance for the directional design of stable high-mobility OSCs.