Synergistic Design of Flexible Substrates and Transparent Electrodes for Application in Organic Photovoltaics: A Review

Flexible organic solar cells (FOSCs) are a promising green energy technology due to their mechanical flexibility, light weight, low cost, and compatibility with large-area solution processing. Although the power conversion efficiency (PCE) of rigid organic solar cells has exceeded 20%, a significant performance gap remains for flexible devices, primarily constrained by the limitations of two key components: the flexible substrate and the transparent electrode. This review systematically summarizes recent research progress on flexible substrates, including ultrathin glass, polymer substrates, stretchable substrates, and bio-based substrates, and flexible transparent electrodes, including ITO, conductive polymers, carbon-based nanomaterials, ultrathin metal films, metal grids, and metal nanowire networks. Building on this, the review explores strategies for the synergistic design of substrates and electrodes, analyzing critical pathways for their co-optimization across four dimensions: interface engineering, mechanical compatibility, optical coupling, and process integration. Examining representative case studies from the literature, optimal substrate–electrode pairings for different application scenarios are summarized. Finally, the review outlines a future perspective on the evolution from compatibility toward functional integration, offering a systematic framework for the development of next-generation flexible photovoltaic devices that are efficient, stable, and adaptable to diverse application requirements.