AgGaSe₂thin films grown by chemical close-spaced vapor transport for photovoltaic applications: structural, compositional and optical properties

Abstract

Thin films of chalcopyrite AgGaSe(2) have been successfully grown on glass and glass/molybdenum substrates using the technique of chemical close-spaced vapor transport. The high crystallinity of the samples is confirmed by grazing-incidence x-ray diffraction, scanning and transmission electron microscopy, and optical transmission/reflection spectroscopy. Here, two of the three expected direct optical bandgaps are found at 1.77(2) and 1.88(6) eV at 300 K. The lowest bandgap energy at 4 K is estimated to be 1.82(3) eV. Photoluminescence spectroscopy has further revealed the nature of the point defects within the AgGaSe(2), showing evidence for the existence of very shallow acceptor levels of 5(1) and 10(1) meV, and thus suggesting the AgGaSe(2) phase itself to exhibit a p-type conductivity. At the same time, electrical characterization by Hall, Seebeck and four-point-probe measurements indicate properties of a compensated semiconductor. The electrical properties of the investigated thin films are mainly influenced by the presence of Ag(2)Se and Ga(2)O(3) nanometer-scaled surface layers, as well as by Ag(2)Se inclusions in the bulk and Ag clusters at the layers' rear side.

Photophysics of polymeric carbon nitride: An optical quasimonomer

“…10,12 Steady-state PL spectra were recorded using the custombuilt setup described elsewhere. 18 The powder samples were fixed on a copper plate using rubber cement and mounted inside a He flow cryostat, allowing for temperatures in the range of 3.5 K T 320 K, equipped with spectrosil B windows. PL was excited with the light of a He-Cd laser (λ = 325 nm), and emission was collected with parabolic mirrors and directed to a Czerny-Turner spectrograph with attached Si-CCD camera.…”

“…PL was excited with the light of a He-Cd laser (λ = 325 nm), and emission was collected with parabolic mirrors and directed to a Czerny-Turner spectrograph with attached Si-CCD camera. The recorded spectra were calibrated using a Hg-line lamp and a calibrated tungsten halogen light source, respectively, as described by Merschjann et al 18 Time-resolved PL data were acquired via the time-resolved single photon counting technique (TRSPC) using a pulsed laser diode emitting at λ = 405 nm with a repetition rate of 1 MHz as light source and a Si Geiger mode APD as photodetector. The temporal response function of the instrument was 100 ps full width at half maximum (FWHM).…”

“…17,18 There is to date no consistent explanation for this finding, although one may speculate that, e.g., the 0-0 transitions could be enhanced at higher excitation powers due to processes yet to be identified.…”

Shining a light on transition metal chalcogenides for sustainable photovoltaics

“…109 The silver analogues have similar properties to the Cu compounds, but can be synthesised under milder conditions. 106 The replacement of cheap copper with relatively expensive silver is unlikely to aid the industrial uptake of this class of material.…”

The Optical Property Characterization of AgGaTe2 Prepared by the Two-Step Closed Space Sublimation

“…The bandgap of AgGaTe 2 at room temperature is 1.3 eV, which is almost the optimum value for fabricating solar cells. This material is one of chalcopyrite I‐III‐VI 2 compounds, which have been recently attracted attention as potential components for semiconductor devices, including solar cells, and electro‐optic devices . The closed space sublimation (CSS) method is widely used in the fabrication of mass production solar cells since it has many advantages for the cost reduction .…”