Timothy J. Peshek

Thin film tandem photovoltaic cell from II-IV-V chalcopyrites

Using quasiparticle self-consistent GW (QSGW) theory, we analyze materials properties of the II-IV-V family of chalcopyrite semiconductors consisting of compounds and alloys based on (Mg,Zn,Cd)(Si,Ge,Sn)(P,As)2, and show how they may offer excellent opportunities for the development of tandem thin-film solar cells. The constituent elements are abundant and nearly lattice-matched compounds can be found with near optimum band gaps. We show the close connection to band structures of other fourfold coordinated compounds that have led to the highest efficiency devices, and suggest potentially optimum alloys for tandem thin-film cells.

ZnGeAs 2 thin films properties: A potentially useful semiconductor for photovoltaic applications

We have studied the chalcopyrite compound ZnGeAs<inf>2</inf> to access its potential as a novel photovoltaic material. Thin films of ZnGeAs2 have been produced by pulsed laser depositionThe films are deposited at 315 °C and are amorphous. They crystallize above 450 °C and improve in crystallinity up to and including 600 °C. At that temperature the Hall mobility is 55 ± 2 cm²/Vs , which is within uncertainty to the highest mobility ever reported for this material. We find a rather high carrier concentration, of order 10¹⁸ – 10¹⁹ for the annealed films, presumably due to the presence of Zn vacancies. The material is an effective light absorber, with an absorption coefficient of order 10⁴ 1/cm at 1.2 eV. These properties suggest ZnGeAs<inf>2</inf> may be used to produce cost effective and efficient solar cells.

Characterization of ZnGeAs 2 thin films produced by pulsed laser deposition

We have characterized the properties of chalcopyrite ZnGeAs2 thin films produced over a wide range of growth conditions using pulsed laser deposition. By using a Zn-enriched target, stoichiometric films could be produced up to a substrate temperature of 315° C; above which the films were Zn and As deficient. Optical absorption measurements indicate that bandgap of the ZnGeAs2 thin films is direct with a value of ∼1.15 eV. Hot point probe indicate that the as-deposited and annealed thin films are both p-type. Hall measurements confirm this and also indicate that the carrier mobility, μp, is over 50 cm2/V·sec in the 600° C annealed samples. Channeling Rutherford Backscattering Spectroscopy (RBS) indicates that the structurally best films are achieved after 450 °C annealing with a channeling yield, ?min, of 50%. Our results, in combination with the observation that the constituents are abundant elements, suggest that ZnGeAs2 is an ideal candidate for photovoltaic applications.

Zero added oxygen for high quality sputtered ITO: A data science investigation of reduced Sn-content and added Zr

The authors demonstrate mobilities of >45 cm2/V s for sputtered tin-doped indium oxide (ITO) films at zero added oxygen. All films were deposited with 5 wt. % SnO2, instead of the more conventional 8–10 wt. %, and had varying ZrO2 content from 0 to 3 wt. %, with a subsequent reduction in In2O3 content. These films were deposited by radio-frequency magnetron sputtering from nominally stoichiometric targets with varying oxygen partial pressure in the sputter ambient. Anomalous behavior was discovered for films with no Zr-added, where a bimodality of high and low mobilities was discovered for nominally similar growth conditions. However, all films showed the lowest resistivity and highest mobilities when the oxygen partial pressure in the sputter ambient was zero. This result is contrasted with several other reports of ITO transport performance having a maximum for small but nonzero oxygen partial pressure. This result is attributed to the reduced concentration of SnO2. The addition of ZrO2 yielded the highe...

Mg-IV-V chalcopyrites in thin film tandem photovoltaic cells

Tandem cells made out II-IV-V chalcopyrites consisting of alloys and compounds of (Mg,Zn,Cd)(Si,Ge,Sn)(P,As)2 are a unique set of candidate materials, that can potentially be optimal for solar cell design. While the Zn- and Cd- based compounds have all been synthesized, little is known about the Mg compounds. We analyze the energy band structure theoretically using a recently developed Quasiparticle Self-consistent GW theory, which enables us to accurately address the electronic structure from first principles.