title: Investigation of cost effective III-V semiconductor solar energy device architecture
Creators: name: Gupta, Bikesh
Publisher: name: The Australian National University
Year: 2024

description: This thesis is dedicated to exploring novel device structures and strategies for cost-effective III-V semiconductor solar energy devices. It includes experimental work and addresses fundamental constraints to develop high-efficiency, cost-effective III-V semiconductor solar devices. The thesis is structured as follows: Chapter 2: This chapter identifies and analyzes the factors contributing to the high cost of III-V semiconductor photovoltaic devices. It aims to overcome cost-related challenges through innovative designs that improve efficiency and economic viability. Chapter 3: This chapter introduces the experimental methods and fabrication techniques used in subsequent chapters (Chapters 4 to 7) to demonstrate high-efficiency and cost-effective InP solar energy devices. Chapter 4: In this chapter, InP heterojunction solar cells are presented, which utilize carrier selectivity and eliminate the need for costly metal organic chemical vapor deposition. TiO2 serves as the electron-selective layer, and H2 plasma exposure modifies the InP surface, resulting in an efficiency of 19.3% and an open-circuit voltage of approximately 800 mV. The effects of H2 plasma exposure on InP photovoltaic devices are discussed. Chapter 5: This chapter introduces an InP heterojunction solar cell with a simplified, cost-effective approach for processing the electron-selective contact layer. A solution-processed ferrihydrite layer is employed as the electron-selective contact, achieving a noteworthy short-circuit current density of 24.7 mA cm-2, comparable to atomic layer-deposited TiO2 (25.8 mA cm-2). Ferrihydrite also acts as a protective shield against InP photocathode photo-corrosion and offers long-term stability, with a photoelectrochemical half-cell water reduction efficiency of 8.4%. Calculations suggest the potential for exceeding 25% efficiency. Chapter 6: This chapter presents a low bandgap InGaAsP solar cell with an efficiency of 19.1% and an open-circuit voltage of 658 mV, rivaling cutting-edge InGaAsP homojunction solar cells. The role of a thin InP surface passivation layer and a TiO2 electron-selective layer in achieving high efficiency is discussed. A mechanically stacked tandem solar cell configuration is developed, achieving an impressive efficiency of 27.7% and an excellent open-circuit voltage of 1.7 V, eliminating the need for lattice-matched tunnel layers. Chapter 7: This chapter addresses cost concerns associated with III-V semiconductor solar cells, particularly related to the use of entire wafers in the manufacturing process. The technique of mechanical peeling off thin InP films from bulk InP wafers (spalling) is introduced. The chapter includes a meticulous assessment of the surfaces of spalled InP thin films to identify potential surface damage. Successful production of InP heterojunction solar cells with an efficiency of 13.3% using spalled thin films is discussed, as well as the creation of a photoanode with promising water oxidation efficiency. Chapter 8: The final chapter consolidates the primary research findings and analyses from the thesis. It also explores potential future research directions for achieving cost-efficient III-V semiconductor solar energy devices. In summary, this thesis contributes significantly to the field of solar energy technology by improving the efficiency and reducing the cost of III-V semiconductor solar cells. The research presents innovative solutions and insights with the potential to advance sustainable and economically viable solar energy technologies.