Electron selective contact in perovskite solar cells

Thesis

Over the last 4 years, perovskite solar cells emerged as an attractive, highly efficient, and low-cost alternative to established, conventional photovoltaic technologies. The power conversion efficiency of these devices recorded an unprecedented rise, currently exceeding certified values of 20%. This thesis covers a number of technological advancements which lead to improved photovoltaic performance, as well as vital insight into some more fundamental aspects of the perovskite device operation. The focus of this body of work is primarily directed towards the electric contact in the PV stack which is responsible for electron collection.

The motivation of the study presented here is given in Chapter 1, and includes a brief summary of the current energy landscape. Chapter 2 introduces the theoretical background of photovoltaic technology, starting from the basics of semiconductor physics, through to the principles of solar cell operation, as well as some characteristic properties of the perovskite materials. Details of the experimental methods used in this study are reported in Chapter 3.

Chapter 4 reports the development of a low temperature process (sub-150 °C) for the manufacture of perovskite solar cells. Dispersions of pre-synthesised, highly crystalline TiO2 nanoparticles were used as an electron selective contact, which eliminated the high temperature sintering step.

Chapters 5, 6 and 7, report the interface modification of an n-type contact, resulting in a substantially improved device operation and suppression of hysteresis phenomenon which is characteristic of perovskite photovoltaics. Fullerene-based materials have been found to make excellent electronic contact with halide perovskite materials, and are shown to be far superior to commonly used metal oxides. The facilitated electron collection allows enhancements in the photovoltaic performance of these devices. Furthermore, the organic layers used in this study can be processed at low temperatures.

Finally, the development of transparent conductive electrodes based on silver nanowires is presented in Chapter 8. The fabricated electrodes exhibit low sheet resistance, high degree of transparency, and can be processed at low temperatures, allowing them to be compatible with processing on flexible substrates and multi-junction architectures. The application of silver nanowires in different perovskite solar cell architectures is also reported.

Authors: Wojciechowski, K

• DOI: 10.5287/ora-e2zarxoe6
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Renewable Energy; Photovoltaics; Condensed Matter Physics; Perovskite Solar Cells