Interface Engineering in Solution-Processed Thin-Film Solar Cells

ConspectusAlong with the rapid industrialization of human society over the past century, incessant energy consumption and endless damage to the environment have aroused growing attention for seeking clean and renewable energy sources. Photovoltaics (PV) that can directly harvest and transform sunlight into electricity have shown great potential in achieving this goal. Especially for solution-processed thin-film solar cells, their extremely cost-effective and facile processing methods compatible with different substrates at large scales exhibit unique advantages over conventional PVs based on crystalline silicon. Various types of solution-processed thin-film PVs have been achieving or already exceeded 15% power conversion efficiency (PCE) through the numerous efforts of researchers. Organic solar cells (OSCs) and organic–inorganic hybrid perovskite solar cells (PVSCs) are the most well-known emerging solution-processed thin-film solar cells that have attracted great interest recently (the PCE of PVSCs soared form 3.8% to over 25% in the past decade). Usually, photogenerated excitons will form as a response to illumination in the active layer, then dissociate into charge carriers, travel in between layers, and finally get collected by electrodes of the device. Besides the broad exploration of active layer materials, suitably matched charge-transporting layers and electrodes also play a vital role in achieving high PCE and stability in PV devices. Furthermore, interfaces between different functional layers created during solution processing need to be carefully addressed to ensure efficient charge transport and prevent degradation. The utilization of proper interfacial materials to modify the chemical and electrical properties at interfaces has become an effective strategy to enhance the performance of PV. Therefore, it is important to develop a comprehensive understanding into the correlation between interfacial properties and charge carrier dynamics and establish molecular design principles for interfacial materials to realize commercialization of emerging PVs.In this Account, we first introduce the fundamental roles of interfaces in PVs, including the modulation of film formation, together with management of charge transport and recombination. Detailed analysis of interfaces and related surface science are also discussed to provide better understanding. Then, we highlight our research on interfacial materials with different functionalities including self-assembled monolayers, dopants, functional molecules for post-treatment, and composite materials. Combining with the fundamental mechanisms and design criteria of interfacial materials, new materials and interface engineering strategies can be integrated into other PV systems to achieve high PCE and stability. In the end, the main challenges and future perspectives toward the commercialization of solution-processed thin-film PVs are discussed to inspire more novel material designs and interface engineering.