Carrier transport study of organic/inorganic solar cells based on device simulation

Abstract

The increasing demand for energy in modern society and the finite storage of traditional fossil fuels have been asking the development of new sustainable energy sources for a long time. Solar energy is one of the promising candidates. In recent years, the solar cell technique develops rapidly, and several kinds of emerging solar cells have been proposed. Focusing on central requirements of low cost and high performance, organic solar cells, and perovskite solar cells are believed to have the potential taking place the role of silicon solar cells. Working as the light absorption layer in solar cells, organic blend and perovskite material have their unique optical and electrical properties. To achieve higher performance, it is desirable to better understand the device physics of the two kinds of cells, particularly the carrier transport mechanism inside the devices, which will directly influence the output power. Here, we aimed to study the carrier generation, transport, and recombination in organic/inorganic solar cells, together with excitonic processes (in organic solar cells) and mobile ion transport (in perovskite solar cells). A new transient simulator based on the modification of drift-diffusion equations was developed to support the theoretical study. Based on the device simulation, the research involved the following work: 1. Exciton delocalization incorporated drift-diffusion study on the bulk-heterojunction organic solar cells Exciton delocalization mechanism in high performance organic solar cells was studied theoretically through device simulation. Exciton kinetics including delocalization, diffusion, and dissociation were incorporated in the drift-diffusion equations, and we comprehensively analyzed the effect of exciton delocalization on the device performance. 2. Theoretical and experimental study of carrier generation and transport for achieving high-performance ternary blend organic solar cells We studied the roles of the carrier generation (e.g. exciton transfer between the components, delocalization, and dissociation), and carrier transport (particularly the hole transport between donors) on the performance of the ternary blend organic solar cells. We analyzed the optical and electrical losses of the device, and critical design rules for improving the device performance were concluded. 3. Transient photovoltage measurements and simulations on perovskite solar cells with varied defect concentrations and inhomogeneous recombination rates We discussed the carrier recombination mechanisms of perovskite solar cells by analyzing the fundamental device physics behind the transient photovoltage measurement. We measured Bi-containing recombination-tunable perovskite solar cells and performed the transient drift-diffusion simulation. It was confirmed by measurement and simulation that transient photovoltage of the normal cells does not carry more information than current-voltage curves, but its decay lifetime can show the inhomogeneities of carrier generation and recombination. 4. Diagnosis of Perovskite Solar Cells by Studying the Characteristic Hysteresis The relations between characteristic J-V hysteresis features and the device flaws caused in the experiments, e.g. bulk or surface defects, low conductivity layers, were comprehensively analyzed through the ion-incorporated transient drift-diffusion simulation. In this work, we assigned the different hysteresis features to several origins and offered a simple and efficient diagnosis method of PSCs through examining the hysteresis features of J-V curves.