Device Physics Study On Antimony Selenide Thin Film Solar Cells

With the increasing requirement for energy and the forthcoming depletion of fossil fuels, as well as the serious environmental pollution caused by fossil fuel burning, researchers around the world are paying greater attention to alternative clean energies, especially on solar cells which convert solar energy to electricity. Even though silicon solar cells are dominant in the current photovoltaic technologies, thin film solar cells(TFSCs) could have special applications for its low weight and excellent flexibility. Despite high solar conversion efficiencies have been achieved, traditional CIGS and Cd Te TFSCs have disadvantages of high cost and toxicity/environmental contamination, respectively. The searching for new materials of TFSCs has been becoming the latest research hot point.Based on deep thinking and literature survey, our group believed that Sb2Se3 is a proper material for optoelectrical devices. Nevertheless, there are very few reports about its application for photovoltaics. Thus, preparation and investigation of Sb2Se3 TFSCs are main focus of this project. In order to achieve high power conversation efficiency, this thesis analyzes device performance from the perspective of device physics, aimed to provide reference for further optimization.The main content of this thesis includes the preparation and device physics analysis of Sb2Se3 TFSCs. Firstly, development of TFSCs, especially Sb2Se3 TFSCs, are introduced. Secondly, focusing on current-voltage, capacitance and external quantum efficiency, the related underlying theory, experimental setup and data analysis are introduced, which laid the foundation for this thesis. Then, this thesis discusses the preparation procedure of Sb2Se3 TFSCs by thermal evaporation and rapid thermal evaporation(RTE), and the optimization process including follow-up annealing and oxygen treatment. Next, I concentrated on carrier transport and loss analysis, and applied the above three characterization methods to calculate device performance, diode and capacitance characteristics of as-fabricated devices. Based on a combination of many theories and a reasonable analysis of characterization results, the key parameters determing open circuit voltage, short circuit current density and fill factor are studied, and the band energy diagram and material characteristics are introduced, preparing for further improvement of device performance.Through optimization, Sb2Se3 TFSCs having 0.33 V open circuit voltage, 22.9 m A/cm2 short circuit current density and 3.58 % efficiency are achieved. Through carrier transport mechanism study, the main limiting factor is belived to be the small open circuit voltage, and the main recombination mechanism is the interface recombination, with the activation energy EA = 0.92 e V. The loss analysis of defect demonstrates that the interface recombination and back contact recombination are two main limiting factors for performance, for the high density of defects detected in these two regions. Furthermore, the analysis of band energy diagram substantiates our recombination theory. Furthermore, the special one-dimensional crystal structure Sb2Se3(composed of(Sb4Se7)n ribbons) is expected to be the essential cause of recombination and loss phenomenon observed in our devices.