Jason Baxter - Academia.edu (original) (raw)
Papers by Jason Baxter
ACS Applied Materials & Interfaces, 2015
ZnS is a wide band gap semiconductor whose many applications, such as photovoltaic buffer layers,... more ZnS is a wide band gap semiconductor whose many applications, such as photovoltaic buffer layers, require uniform and continuous films down to several nanometers thick. Chemical bath deposition (CBD) is a simple, low-cost, and scalable technique to deposit such inorganic films. However, previous attempts at CBD of ZnS have often resulted in nodular noncontinuous films, slow growth rates at low pH, and high ratio of oxygen impurities at high pH. In this work, ZnS thin films were grown by adding hexamethylenetetramine (HMTA) to a conventional recipe that uses zinc sulfate, nitrilotriacetic acid trisodium salt, and thioacetamide. Dynamic bath characterization showed that HMTA helps the bath to maintain near-neutral pH and also acts as a catalyst, which leads to fast nucleation and deposition rates, continuous films, and less oxygen impurities in the films. Films deposited on glass from HMTA-containing bath were uniform, continuous, and 90 nm thick after 1 h, as opposed to films grown without HMTA that were ∼3 times thinner and more nodular. On Cu2(Zn,Sn)Se4, films grown with HMTA were continuous within 10 min. The films have comparatively few oxygen impurities, with S/(S + O) atomic ratio of 88%, and high optical transmission of 98% at 360 nm. The Zn(S,O,OH) films exhibit excellent adhesion to glass and high resistivity, which make them ideal nucleation layers for other metal sulfides. Their promise as a nucleation layer was demonstrated with the deposition of thin, continuous Sb2S3 overlayers. This novel HMTA chemistry enables rapid deposition of Zn(S,O,OH) thin films to serve as a nucleation layer, a photovoltaic buffer layer, or an extremely thin continuous coating for thin film applications. HMTA may also be applied in a similar manner for solution deposition of other metal chalcogenide and oxide thin films with superior properties.
Solar Energy Materials and Solar Cells, 2006
ZnO nanowires and structures that combine nanowires and nanoparticles were used as the wide band ... more ZnO nanowires and structures that combine nanowires and nanoparticles were used as the wide band gap semiconducting photoelectrode in dye-sensitized solar cells (DSSCs). The nanowires provide a direct path from the point of photogeneration to the conducting substrate and offer alternative semiconductor network morphologies to those possible with sintered nanoparticles. Growing nanowires with dendrite-like branched structure greatly enhances their surface area, leading to improved light harvesting and overall efficiencies. Hybrid cells based on a combination of nanowires and nanoparticles can be tailored to take advantage of both the high surface area provided by the nanoparticles and the improved electron transport along a nanowire network. Solar cells made from branched nanowires showed photocurrents of 1.6 mA/cm 2 , internal quantum efficiencies of 70%, and overall efficiencies of 0.5%. Solar cells made from appropriate hybrid morphologies show photocurrents of 3 mA/cm 2 and overall efficiencies of 1.1%, while both the nanowire and hybrid cells show larger open circuit voltages than nanoparticle cells.
ACS Applied Materials & Interfaces, 2015
ZnS is a wide band gap semiconductor whose many applications, such as photovoltaic buffer layers,... more ZnS is a wide band gap semiconductor whose many applications, such as photovoltaic buffer layers, require uniform and continuous films down to several nanometers thick. Chemical bath deposition (CBD) is a simple, low-cost, and scalable technique to deposit such inorganic films. However, previous attempts at CBD of ZnS have often resulted in nodular noncontinuous films, slow growth rates at low pH, and high ratio of oxygen impurities at high pH. In this work, ZnS thin films were grown by adding hexamethylenetetramine (HMTA) to a conventional recipe that uses zinc sulfate, nitrilotriacetic acid trisodium salt, and thioacetamide. Dynamic bath characterization showed that HMTA helps the bath to maintain near-neutral pH and also acts as a catalyst, which leads to fast nucleation and deposition rates, continuous films, and less oxygen impurities in the films. Films deposited on glass from HMTA-containing bath were uniform, continuous, and 90 nm thick after 1 h, as opposed to films grown without HMTA that were ∼3 times thinner and more nodular. On Cu2(Zn,Sn)Se4, films grown with HMTA were continuous within 10 min. The films have comparatively few oxygen impurities, with S/(S + O) atomic ratio of 88%, and high optical transmission of 98% at 360 nm. The Zn(S,O,OH) films exhibit excellent adhesion to glass and high resistivity, which make them ideal nucleation layers for other metal sulfides. Their promise as a nucleation layer was demonstrated with the deposition of thin, continuous Sb2S3 overlayers. This novel HMTA chemistry enables rapid deposition of Zn(S,O,OH) thin films to serve as a nucleation layer, a photovoltaic buffer layer, or an extremely thin continuous coating for thin film applications. HMTA may also be applied in a similar manner for solution deposition of other metal chalcogenide and oxide thin films with superior properties.
Solar Energy Materials and Solar Cells, 2006
ZnO nanowires and structures that combine nanowires and nanoparticles were used as the wide band ... more ZnO nanowires and structures that combine nanowires and nanoparticles were used as the wide band gap semiconducting photoelectrode in dye-sensitized solar cells (DSSCs). The nanowires provide a direct path from the point of photogeneration to the conducting substrate and offer alternative semiconductor network morphologies to those possible with sintered nanoparticles. Growing nanowires with dendrite-like branched structure greatly enhances their surface area, leading to improved light harvesting and overall efficiencies. Hybrid cells based on a combination of nanowires and nanoparticles can be tailored to take advantage of both the high surface area provided by the nanoparticles and the improved electron transport along a nanowire network. Solar cells made from branched nanowires showed photocurrents of 1.6 mA/cm 2 , internal quantum efficiencies of 70%, and overall efficiencies of 0.5%. Solar cells made from appropriate hybrid morphologies show photocurrents of 3 mA/cm 2 and overall efficiencies of 1.1%, while both the nanowire and hybrid cells show larger open circuit voltages than nanoparticle cells.