Optimizing Light Absorption and Nanomorphology in Organic Solar Cells and Near-IR Photodetectors with Ternary Blend Approaches

Abstract

Solution-processed Organic Solar cells (OSCs) are a promising renewable energy solution due to their solution-processable roll-to-roll fabrication, semitransparency, lightweight, and flexibility. Significant efforts have been focused on designing efficient electron-donating polymers to blend with fullerene and non-fullerene-based electron acceptors. While OSCs have achieved power conversion efficiency (PCE) close to 20%, they still lag behind silicon and perovskite solar cells. The active layer, composed of a donor-acceptor mixture, suffers from many challenges, such as limited absorption coverage within the solar spectrum, uncontrolled nanomorphology, and high non-radiative recombination losses. Interestingly, the ternary blend approach offers a way to address the narrow-band absorption issue, and along with that, it also affects the nanomorphology. This demands the rational approach to choose a third component to optimize both nanomorphology and light absorption. In my thesis, I have thoroughly investigated the selection of a third component in binary blend OSCs, highlighting its benefits such as enhanced light harvesting, improved short-circuit current density (JSC), and tunable open-circuit voltage (VOC) through energy level alignment and reduced recombination losses. We demonstrated how the inclusion of linearly linked perylene diimide (PDI) chromophores impacts the bulk heterojunction morphology, leading to enhanced device performance. Additionally, I studied the critical role of interface modification in charge extraction, showing how it helps to minimize recombination losses. By optimizing the interface, we significantly reduced non-radiative recombination losses. Lastly, with the improved nanomorphology of our ternary blend bulk heterojunction, I successfully suppressed dark current density and enhanced photodetection in near-IR organic photodetectors.