Date on Master's Thesis/Doctoral Dissertation

5-2012

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Chemical Engineering

Committee Chair

Fu, Xiao-An

Author's Keywords

Photovoltaic; Microfabrication; Sputter; Solar cell; Germanium; Multijunction

Subject

Solar cells; Thin films

Abstract

Microfabricated planar solar cells with an active solar collection area of 0.04cm2 were fabricated on n-type silicon wafers to test the viability of sputtered amorphous thin film photovoltaics for potential use in amorphous multijunction cells or inexpensive laser detectors. Several variants based on the same photovoltaic cell design were produced using amorphous silicon, amorphous germanium, and amorphous germanium-tin to explore band gap depression phenomenon in amorphous thin films that had been previously described in crystalline germanium-tin and germanium-silicon-tin alloys. UV/VIS spectroscopy and Tauc Plot band gap analysis indicated that tin inclusion led to band gap depression of 0.046 eV for every percentage increase in tin content in co-sputtered germanium-tin films. In sputtered amorphous germanium-tin films, increases in average incident photon conversion efficiency of 1.93% for Sn.05Ge.95 and 2.95% for Sn.10Ge.90 as compared to germanium only films were observed. Overall cell efficiency increases were also observed with the inclusion of tin by 0.68% for Sn.05Ge.95 and 0.78% for Sn.10Ge.90 when compared to germanium films. Comparing sputtered germanium films to PECVD deposited amorphous silicon films, the sputtered germanium films displayed significantly lower overall conversion efficiencies and incident photon conversion efficiencies. When comparing to amorphous silicon thin films, improved absorption of longer wavelength radiation in the IR and NIR range was expected with germanium and tin thin films exhibiting band gap depression phenomenon.

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