Solution processed Cu(In,Ga)S2 thin film and nanowire photovoltaics

Solar energy conversion is a highly attractive process for clean and renewable power for the future. Cu(In,Ga)(Se,S)2/CdS/ZnO has proven itself to be a worthwhile photovoltaic combination achieving record efficiencies upwards of 20%. These record efficiencies have been obtained through vacuum-based approaches. However, the high cost of vacuum-based fabrication processes become a barrier to affordable solar cells as an energy source. As a result, solution-based approaches have become the focus of many studies which have achieved record efficiencies of 15%. These solution-based approaches have not matched up with the vacuum-based approaches. In this work, we investigate methods to improve the solution-based Cu(In,Ga)(Se,S)2 solar cell.;We have fabricated thin film devices with efficiencies on par to the record solution processed devices at 12.48%. This was achieved through direct control over elemental compositions, ideally Cu and Ga, and crystallinity of the thin film. Inverted thin films, called superstrate structures, were fabricated yielding device performance of 1.38%. The goal of this project is to incorporate nanowires into superstrate structures to improve the device performance by increasing the light conversion.;An emerging solar cell design is to transfer the typical 2-dimensional structure into a 3-dimensional one by utilizing 1-dimensional nanostructures to build devices in an "up and out" fashion. ZnO nanostructures have been of high interest in the research community due to their enhanced physical properties in comparison to bulk materials. This makes them an ideal structure to incorporate them into the foundation of the solar cell. The benefit of utilizing the 3-dimensional design into these Cu(In,Ga)(Se,S)2 solar cells is to enhance the light absorption through light trapping, increase the surface area of the device, and enhance the charge collection. These all hold a key into increasing the device performance. Device structures were fabricated and the performance exceeded the superstrate devices with power conversion efficiencies up to 4.1%.;We can also improve the device by making it more environmentally friendly by replacing the harmful and toxic CdS buffer layer. Mg doped ZnO, an abundant and environmentally friendly material, is an emerging material that has shown to be useful as a buffer layer in solar cell applications. MgZnO buffer layers yielded similar results as CdS for thin film devices with 12.4% efficiency. And MgZnO showed to be a better choice than CdS in the superstrate and nanowire designs due to an increased thermal stability.;This is the first report of improving solution-based CIGS solar cells by enhancing the material properties and also by incorporating a new design, 3-dimensioned structures, into the devices.