Simultaneous improvements in self-cleaning and light-trapping abilities of polymer substrates for flexible organic solar cells

Organic solar cells (OSCs) supported on mechanically flexible and optically transparent polymer substrates have been receiving increased attention owing to their noticeable merits of low cost, light weight, and flexible design that are unattainable by their existing counterparts supported on rigid glass substrates. However, technical issues such as relatively low photon-to-electron conversion efficiencies and long-term stabilities of OSCs on polymer substrates require the enhancement and maintenance of the efficiency of OSCs. In this study, a simple, direct vacuum deposition strategy was used to fabricate a multifunctional silica nanoparticle array (SNA) layer on polymer substrates for improving and maintaining the light harvesting efficiencies of OSCs; this induces simultaneous and significant enhancements in the light-scattering and contaminant-repelling (or self-cleaning) properties of the substrate. The SNA layer led to improved light scattering features, representing haze transmittances ranging from 3.4% to 80.4% in the visible spectral range with strong influences of its geometrical features on the hydrophobic/oleophobic characteristics of the substrate. Any contaminant-induced reduction in the performance of OSCs could be successfully prevented by the strong contaminant-repelling feature, characterized by high contact angles (>150 degrees) and low sliding angles (<15 degrees) for water and ethylene glycol, without compromising the optical transparency of the polymer substrate. A combination of the SNA layer and oxide/metal/oxide (OMO) electrode coating on each side of the polymer substrate provides a promising solution to improve the performance of OSCs. The power conversion efficiency was enhanced by 13.31% compared to that of an OSC based on the same polymer substrate without the SNA layer.