Earth-Abundant Thin-Film Devices for Photovoltaic and Electrochemical Applications

Abstract

Humanity faces a host of unprecedented challenges in the 21st century which will require inexpensive, scalable technological solutions. This thesis focuses on the technological development of devices which address two of these 21st-century challenges: global climate change and increasing pharmaceutical contamination of water supplies. Solution-processed Cu2ZnSnSe4 (CZTS) photovoltaic (PV) devices are a promising technology for next-generation PV devices because of their earth-abundant constituents and ability to be scaled up with roll-to-roll processing. This work identifies critical processing parameters during CZTS solution deposition to prevent the formation of amorphous carbon nitride impurity phases which ruin device performance. Discovery of new complexation chemistries in CZTS solutions allowed for the stabilization of a wide range of metal chloride species via Lewis acid-base interactions. This facilitated a novel silver and germanium co-alloying strategy in CZTS which led to devices with record high performance metrics. Electrochemical oxidation is a promising technology to remediate pharmaceuticals in wastewaters, but current technologies lead to the inadvertent generation of ClO3-, ClO4-, and other toxic byproducts (TBPs) which are more hazardous than many pharmaceuticals. This work is the first to identify that the high nitrogen content in human urine (which contain the majority of excreted pharmaceuticals) suppress ClO3- and ClO4- formation by 3 orders of magnitude. A novel, inexpensive device scheme was developed to treat pharmaceutical-contaminated urine at the source of generation. This device consists of a series of divided electrochemical cells which control pH via H2 and O2 evolution, and sequence oxidation/reduction such that pharmaceuticals are oxidized while ClO3-, ClO4-, and other TBPs are reduced.