Next generation thin film photovoltaics [electronic resource] : study and application of surface modification and atomic layer deposition

Solar energy is the most abundant renewable energy resource and is compatible with both utility scale and distributed power applications. Silicon photovoltaics are well established and dominate the market today; however, as silicon technology approaches practical efficiency limitations, we must look toward the next generation of photovoltaic materials. Two promising candidates are quantum dots and metal halide perovskites that have advantages such as low-cost solution processing, a direct and tunable band gap with a high absorption coefficient, and tolerance to defects and impurities. These materials offer the potential to not only reduce the levelized cost of electricity through low-cost manufacturing, but also to increase efficiency through tandem or multi-junction architectures. However, improvements to the stability and efficiency of these devices are required for commercialization. The surfaces and interfaces are critically important to the recombination and charge transport properties that dictate the operation of these thin film devices. In this research, we work to better understand the effects of organic surface species and atomic layer deposition (ALD) processing applied to quantum dot and metal halide perovskite materials. The knowledge gained from these studies is applied to improve thin film photovoltaic devices. Herein, we demonstrate a method to fabricate a graded band structure in colloidal quantum dot photovoltaics through ligand dipole tuning. Proper choice of quantum dot surface ligands creates a favorable alignment between quantum dot layers in order to improve charge separation and device performance. We also present a study of tin oxide ALD on metal halide perovskite thin films and the effects of fullerene layers at the perovskite surface. A low-temperature ALD tin oxide method is developed that enables the sputtering of a transparent indium-tin-oxide electrode on wide-gap perovskite solar cells with high optical transmission in the infrared. This device architecture is shown to have impressive stability, passing the International Electrotechnical Commission (IEC) 61215 accelerated lifetime testing protocol applied to silicon modules. Furthermore, the semitransparent perovskite device is fabricated on top of an infrared-optimized silicon heterojunction solar cell to form a monolithic perovskite/silicon tandem device with a high open circuit voltage of 1.65 V and a certified solar conversion efficiency of 23.6 %, the highest reported monolithic tandem perovskite solar cell efficiency to date. The high photovoltage of this device is sufficient to drive photoelectrochemical water splitting, enabling the conversion of solar energy to chemical bonds for energy storage in the form of hydrogen gas. ALD TiO2 and polymer coatings were applied to demonstrate perovskite-based PEC device operation in aqueous electrolyte for 1 hour and an unassisted initial solar-to-hydrogen conversion efficiency of 4 %.

Keywords: Chemical Engineering.
Advisor: Bent Stacey primary advisor. Thesis advisor
Bao Zhenan advisor. Thesis advisor
McGehee Michael