Solution Deposition of Semiconductor Thin Films for Photovoltaics

Download or read book Solution Deposition of Semiconductor Thin Films for Photovoltaics written by Steven Michael Herron and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Thin film photovoltaics are among the most promising clean, renewable energy technologies and have the potential to meet future world energy demand by covering only a small fraction of the earth's surface. To meet this challenge, annual production of photovoltaic modules, despite recent escalation, must still increase several orders of magnitude, and the development of inexpensive and scalable thin film deposition methods is of crucial importance to this effort. The cost and scalability limitations of the standard high-vacuum thin film deposition methods may be overcome by using solution-based methods. Furthermore, the transition from photovoltaic materials containing cadmium, indium, and tellurium to materials comprised of earth-abundant, non-toxic elements is expected to accelerate their large-scale deployment. Here, I present several strategies for the improvement of inorganic thin films synthesized by solution deposition. In this work, two low-cost, solution-based methods (chemical bath deposition and nanocrystal inks) were applied to the deposition of thin films of ZnS, SnS, and Cu2ZnSnS4 (CZTS), all potential earth-abundant non-toxic materials for photovoltaics. First, through the chemical bath deposition of SnS, I show how film quality is a function of deposition kinetics and can be manipulated through control of bath compositions and post-annealing parameters to improve film properties In the same SnS system, using nanocrystal inks, I show that control over nanocrystal morphology can be used as a strategy for improving thin film quality. A selective synthesis was developed for the production of high-aspect ratio sheet-like nanocrystals. Nanocrystal inks formulated from these crystals were capable of producing extremely highly-oriented thin films through the lamellar stacking of SnS sheets, which yielded favorable optical and electronic properties. The second major study in nanocrystal inks examined the efficacy of inorganic ligand exchanges and the resulting effect on film formation. Ammonium polysulfides were demonstrated as a novel species for ligand exchange on cubic ZnS nanocrystals, where they were shown to remove native ligands with high efficacy and improve film quality. Finally, this ligand exchange was applied to CZTS nanocrystal inks with promising implications for the deposition solar absorber layers. The use of these ligands has the potential to improve efficiency and lower costs in the production of CZTS photovoltaics and other chalcogenide thin films.