Highly Efficient Light Harvesting for High-Performance Polymer Solar Cells

Abstract

Polymer solar cells (PSCs) have gained a lot of attention due to their promising merits such as low cost, mechanical flexibility and solution processability for large area fabrication. Of various strategies, the surface plasmon resonance (SPR) effect using metal nanoparticles (MNPs), morphology control by processing additives, and ternary blend based bulkheterojunction (BHJ) are promising and efficient method to lead to maximizing the performance of PSCs. First, SPR effect from a localized electromagnetic surface wave at the metal and dielectric interface is effective way to enable active layer to absorb more incident light by field enhancement near MNPs. Second, morphology control by processing additives is one of the efficient methods to improve the PSCs accompanied with various morphology engineerings such as nanofibrilar structure, smooth surface, vertical phase separation etc.. Third, ternary blend sytem of PSCs is also promising engineering to achicve many advantages including compensated light absorption and tuning of built-in potential of BHJ. Here, I report the SPR effect using PEDOT electrode incorporated with silver nanopartices (Ag NPs) for highly efficient ITO-free PSCs and polymer light-emitting diodes (PLEDs). Ag NPs can be easily synthesized and then dissolved in PEDOT:PSS electorode. This PEDOT:PSS electrode with Ag NPs electrode contributes to increments in light absorption/emission in the active layer, respectively, by enhanced electric field distribution. I also report morphology engineering of active layer using various conjugated polymers and processing additives with thick active layer to obtain more light absorption and higher efficieny with thick active layer. PSCs based on semi-crystalline, low band gap (LBG) polymers are fabricated with single-cell architecture using diphenyl ether (DPE) as a processing additive. By using DPE additive, the semi-crystalline polymer, PPDT2FBT, form a well-distributed nano-fibrillar networked morphology with PC71BM with balanced hole and electron mobilities. Notably, PPDT2FBT:PC71BM with DPE shows high efficiency event at ~ 1μm film thickness with well-formed isotropic morphology. DTDPPTT (P2) polymer also demonstrate bicontinuous interpenetrating donor:acceptor (D:A) network in both lateral and vertical direction of thick BHJ film with DPE additive. Finally, I present efficient ternary PSCs via the incorporation of both PC61BM and PC71BM mixture as mixed acceptors and the conjugated polymer, PTBT as a donor. This ternary blend system results in a remarkable improvement in the power conversion efficieny compared to binary mixtures of the components via enhanced light absorption by PC71BM and balanced chargetransport by PC61BM. These virious and efficient methods using plasmonic MNPs, morphology engineering, and ternary blend may offer possibility for commercialization of PSCs.