Organic Solar Cells Surpassing 20% Power Conversion Efficiency: Material Innovations, Device Engineering, and Pathways to Flexible Power Suppliers
Organic solar cells (OSCs) have transitioned from <1% initial power conversion efficiency (PCE) to a benchmark exceeding 20% in single-junction and tandem architectures, marking a critical milestone for solution-processable photovoltaics. This review consolidates recent reports (2022–2025) on OSCs with PCE >20%, analyzing key strategies: photoactive material innovation (wide-bandgap polymer donors, narrow-bandgap non-fullerene acceptors), multi-component system construction, deposition protocol optimization, solid/solvent additive engineering, and hole/electron transport layer development. Empirical data from 15 high-impact studies reveal PCEs of 20.0–20.6% in single-junction devices and 20.2–26% in perovskite/organic tandem cells, with interfacial engineering (e.g., yttrium phosphotungstate, carbazole-modified 2PACz, naphthalene diimide interlayers) suppressing bimolecular recombination and enabling scalable large-area fabrication. Operational stability remains a bottleneck: amide-based cathode interlayers achieve 20% PCE with dual-modification mechanisms, while self-assembled monolayers enable hole transport layer-free devices with 18% efficiency and improved stability. The review identifies next-stage challenges: reducing voltage losses (to <0.5 V), scaling deposition uniformity beyond 100 cm², and achieving cost parity with silicon (<$0.30/Wp). These issues are critical for flexible and wearable power suppliers, where mechanical durability (<5% PCE degradation after 1000 bending cycles) and low-temperature processing (<150°C) are mandatory. The analysis provides a roadmap for industrial translation, emphasizing that material–device co-optimization, rather than isolated breakthroughs, will determine commercial viability.