Graphene as transparent electrodes for solar cells

Abstract

The aim of this thesis is to develop an understanding of the science and engineering in applying chemical vapor deposition (CVD) graphene as the transparent conductor in photovoltaic devices. Transparent conducting oxides currently dominate the transparent conductor market but suffer drawbacks that make them unsuitable certain applications. Graphene is mechanically robust, chemically inert, and has work function that can be tuned by chemical doping, making it a versatile substitute that is compatible many types of devices. We start by demonstrating a scalable method for directly transferring graphene onto a variety of substrates and exploring a doping method that vastly enhances the conductivity of graphene films. These developments improve the attractiveness of CVD graphene for transparent electrode applications. Next, we apply graphene to various types of devices to assess key advantages and challenges. We develop an understanding of the importance of the interface in graphene/silicon Schottky barrier solar cells and apply our understanding to achieve record efficiency in these devices. We also explore graphene/SrTiO₃ Schottky junctions, where the graphene itself is responsible for absorbing visible light and show that these devices can be used as tunable photodetectors. We demonstrate highly-transparent organic solar cells with all-graphene electrode as well as inkjet-printed perovskite solar cells with graphene electrodes. Finally, we use graphene/perovskite Schottky barrier solar cells to gain a better understanding of carrier dynamics in perovskite films.