Date on Master's Thesis/Doctoral Dissertation

8-2017

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemical Engineering

Degree Program

Chemical Engineering, PhD

Committee Chair

Sunkara, Mahendra

Committee Co-Chair (if applicable)

Druffel, Thad

Committee Member

Fu, Xiao-an

Committee Member

Starr, Thomas

Committee Member

Atre, Sundar

Author's Keywords

solar cells; photovoltaics; cadmium telluride; perovskite; thin film; electrodeposition

Abstract

A growing population along with developing nations are increasing the demand for energy. The International Energy Agency forecasts a global electricity demand increase of 70 percent by 2040. This is an increase from nearly 18 TW to over 30 TW. The sun can be a great clean source of achieving this energy demand. Despite the large solar industry development, the market is still growing as solar energy only accounted for 0.87% of the global energy production in 2013. The opportunity exists to manufacture more affordable solar energy that can penetrate more of the global energy market. In this dissertation, a photonic-based manufacturing technique called intense pulsed light (IPL) was investigated to enhance the photovoltaic properties of CdTe, better understand the CdCl2 treatment used to create higher efficiency CdTe solar devices, enable the first sintering and efficiency enhancement of perovskite solar cell (PSC), and study the possible conversion of a stable 2D perovskite to a 3D perovskite. CdTe thin films grown by low temperature electrodeposition were treated for the first time with IPL. The low temperature electrodeposition growth resulted in films consisting of nanoparticles, with reduced melting point temperatures. In combination with the high temperature rise produced by the pulses of light, the lower melting temperature resulted in pores/voids being filled as well as enhanced grain growth. As a result, pin-holes and grain boundary recombination were diminished. Subsequently the fill factors of PV devices created using this technology significantly increased. In addition, the IPL also successfully improved the crystallinity in the CdTe films by photonically initiating the popular CdCl2 treatment. To understand the mystery behind the mechanism of the CdCl2 treatment, low temperature PL was utilized and new electrodeposition precursors resulting from the study improved device efficiencies. Photoactive perovskite CH3NH3PbI3 layers were successfully sintered with a novel IPL treatment with efficiencies exceeding 12%. The processing time was reduced to 2 ms, which was significantly faster than those from previous reports. Additionally, the average performance of the IPL-processed samples showed an improvement compared to the hot- plate-processed samples. This advance creates an exciting new method to quickly create dense layers of perovskite, eliminating the rate-limiting annealing step detrimental to industry adoption, and shows the first known occurrence of sintering in CH3NH3PbI3 perovskite particles. Lastly, the fast photonic processing of the IPL enabled the first conversion of a stable 2D perovskite structure into a 3D structure. This caused an band gap shift from 2.0 eV to 1.6 eV and showed the capabilities of band gap tuning enabled by the IPL. While this work is the first documentation of band gap tuning enabled by a photonic effect, it presents a possible inexpensive manufacturing technique that could use one material to create several different colors for the future development of pixel-based LED displays.

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