Solar Cells from Multinary Nanocrystal Inks
Abstract
Solar energy is an abundant, distributed resource requiring continued reductions in manufacturing costs before widespread adoption will occur on economic grounds. Thin film photovoltaics represent a viable technology to economically harness this solar energy, but the formation of the light absorbing layer remains as a critical challenge. This work focuses on the development of a process involving the printing of nanocrystal inks followed by a sintering step to form photovoltaic quality light absorbing layers. Nanocrystal ink deposition is accomplished using a low cost coating technique amenable to scale up for the heavily researched Cu(In,Ga)(S,Se)2 light absorbing layer as well as a relatively new thin film photovoltaic material, Cu 2ZnSn(S,Se)4. External Quantum Efficiency measurements in conjunction with modeling reveal the effect of deep traps in the CdS layer for solar cells consisting of a CdS/CuIn(S,Se)2 pn junction. Nanocrystals synthesized with various Cu and In salt precursors are fabricated into solar cells and the choice of precursor is determined to have no significant effect on the resulting device performance. The nature of a particle-like layer that forms during the nanocrystal sintering process is extensively investigated, and demonstrated to be mitigated by controlling nanocrystal size. The relatively new Cu 2ZnSn(S,Se)4 material system is expanded to include Ge, forming Cu2Zn(Sn,Ge)(S,Se)4. This photovoltaic material is shown to be suitable for fabrication of efficient solar cells, with a band gap readily controlled by manipulation of the germanium content.
Degree
Ph.D.
Advisors
Hillhouse, Purdue University.
Subject Area
Chemical engineering
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