Interfacial Engineering and Surface Plasmon Resonance Effect for High-Performance Polymer Solar Cells

Abstract

Polymer solar cells (PSCs) have attracted great attention because of their many advantages including flexibility, light weight, and low fabrication cost. Among various strategies, the interfacial engineering and surface plasmon resonance (SPR) effect of metal nanoparticles (NPs) are promising and efficient ways to maximize performance of PSCs. Interfacial engineering can passivate charge trap sites, control energy level alignment, enhance charge extraction, guide active layer morphology, improve materials compatibility, alter work functions of anode and cathode. In addition, SPR effect of metal NPs can be an effective way to store the incident light energy in localized surface plasmon modes and enhance the photogeneration of excitons. Here, I present various interfacial engineering strategies employing novel charge transport layer, such as combined layer of metal oxide/ionic liquids (IL) and metal oxide/conjugated polyelectrolyte (CPE). Ionic dipoles within IL layer effectively influenced the work function of the metal oxide and thus the electron injection/transport barrier between the conduction band of metal oxide and the LUMO of active layer could be efficiently reduced. In addition, spontaneously oriented interfacial dipoles within the CPE layer lower the energy barrier for electron injection/transport and reduce the interfacial contact resistance and inherent incompatibility between the hydrophilic metal oxide and hydrophobic active layers. Surface modification of metal oxide with fullerene-based self-assembled monolayer (FSAM) reduced the contact resistance and inherent incompatibility at the metal oxide/active layer interface, resulting in an improved device performance. I also present various plasmonic materials, such as carbon dot-supported silver NPs (CD-Ag NPs), silica-coated Ag NPs (Ag@SiO2), and solvent-mediated Ag NPs (Ag@NMP) for high-performance PSCs. Compared to previous plasmonic materials, CD-Ag NPs led to broad light absorption originating from the ensemble of plasmon coupling effect caused by clustering Ag NPs in CD-Ag NPs. Furthermore, incorporating Ag@SiO2 between hole transport layer and active layer led to remarkable improvement in device efficiency caused by increased light absorption and scattering via enhanced electric field distribution. These versatile and effective methods using interfacial engineering and plasmonic materials may offer possibility to commercialize organic optoelectronic devices.