UCLA

Thin film solar cells have attracted considerable attentions due to their lightweight, low material consumption, ease of fabrication, and potentially high power-conversion efficiency. However, significant cost reductions as well as large-scale production are necessary to compete with the conventional utility power. To reduce cost, vacuum-free manufacture process for each solar cell component is needed. This dissertation focus on novel and cost-effective methods on solution processes of thin film solar cells, ranged from top transparent electrode, the various absorbing layers, and eventually achieving high performance devices. For the transparent electrode, our focus is on the silver nano-wires, and the nano-junction within the network. For the absorbing layer, our targets are: Cu2ZnSn(S,Se)4 (CZTS), and CH3NH3PbX3 (MAX, X= I, Cl, Br) perovskite materials, respectively. In Chapter 2, a formation of Ag-NW contacts was proven to be an efficient method to reduce the contact resistance using the Joule heating, current crowding, and electromigration effect. Transparent electrodes have been applied to optoelectronic devices. Chapter 3, a metal nanowire composite layer was demonstrated to achieve fully solution-processed as a component of CuIn(S,Se)4 (CISS) solar cells. The high performance of the nanowire composite and the role of such electrodes in high performance solar devices were elucidated. Further improvement of the nanowire network to achieve better stability was also demonstrated. Chapter 4 presented a doping control method to investigate the effect of sodium dopant to the CZTS solar cells in terms of device performance, properties, and film formation. A novel synthesis method of CZTS:Na nanocrystal was demonstrated. Sodium incorporation method successfully improved the efficiency by around 50%. In addition, the role of sodium incorporation was investigated. In Chapter 5, the transformation of solution-processed MAX3 perovskite solar cells was investigated and possible reaction pathways were proposed. Secondary phases from this process were identified and the corresponding physical properties during the transformation were further studied.