Top electrode and interfacial engineering for high-performance photovoltaics

Abstract

Environmental and storage issues make photovoltaic technology critical in next-generation energy consumption. The rapid developments of various photovoltaics—such as silicon-based, thin-film, and emerging solar cells—have recently attracted much attention. Compared with silicon-based and thin-film solar cells, the emerging solar cells exhibit low cost, superior flexibility, and competitive power conversion efficiency (PCE). The main components of emerging photovoltaic technologies are organic and perovskite solar cells, which have achieved PCEs of over 19% and 25% for single-junction cells, contributed by the well-developed material science and structure design. However, the typical deposition methods for rear electrodes in solar cells are thermal evaporation and magnetron sputtering, which consume vast amounts of energy and are difficult to employ for scale-up applications. Thus, scale-up deposition methods are essential to realizing the industrialization of solar cells. Solution-processed top electrodes (STEs)—such as conductive polymers, carbon-based nanomaterials, and metal-based materials—are potential candidates. The transparent electrodes are suitable for semi-transparent applications, and the high-reflectance electrodes can act as rear electrodes. Nevertheless, the performance of evaporation-free photovoltaics suffers from poor optical and electrical properties of STEs and severe interfacial issues. Thus, we conducted three studies to solve the issues and drive all solution-processed photovoltaics to the commercial stage. 1. Propose a polymer-anchored silver nanowires electrode with good stability for high-performance semi-transparent organic photovoltaics (OPVs) A one-step post-treatment is introduced to the AgNW networks to achieve high transmittance and good interfacial contact. The high intensity of functional groups can strongly interact with the Ag surface and anchor the AgNWs on an atomic scale, and structured polymers further improve the activation tolerance, resulting in improved thermal, electrical, chemical, and mechanical stabilities of AgNW networks. Semi-transparent OPVs with the treated AgNW electrode simultaneously show high performance and transmittance. Assisted by a cooling mirror with a suitable cutoff wavelength, a competitive light utilized efficiency is achieved. 2. Build a guideline for selecting ligands for solution processed AgNP electrodes with high broadband reflectance. The GA is employed in the synthesis process to achieve uniform particle size, good dispersion in polar solvents, and ideal storage stability of AgNPs. Short chain and multiple functional groups contribute to high packing density of Ag. After annealing at a relatively low temperature, the AgNP films rapidly sinter due to the decarboxylic reaction of GA and present high conductivity and reflectance. The OPVs with AgNP electrodes exhibit high PCEs of 15.23% for a small area and 14.69% for a large area. 3. Uncover the interfacial issues in perovskite solar cells (PSCs) and apply a series of Lewis base molecules with different functional groups to achieve high-performance and stable PSCs Lewis base molecules are introduced to the interface between the electron transporting layer and perovskite to modify the interface for fewer interfacial defects and better energy level alignment. The functional groups with different electron affinities can significantly influence the interfacial modifications. The modified PSCs show an improved PCE and better operational stability. (483 words)