Recent progress in organic solar cells (Part II device engineering)

Organic solar cells (OSCs) have gained a rapid development in the past two decades and the power conversion efficiency (PCE) of single-junction OSC has recently approached 20%. The novel materials and device engineering are two key factors of this evolution. In this review, the device engineering, including morphology characterization and optimization, device physics, flexible and large-area OSCs, and stability of OSCs are systematically summarized. In addition, the current challenges, problems and future developments are also discussed.