Vacancy defects and optoelectrical properties for fluorine tin oxide thin films with various SnF2 contents

Abstract

Fluorine doped tin oxide (FTO) thin films were deposited on glass substrates by e-beam evaporation. Much higher carrier concentration, broader optical band gap, and average transmittance over 80% were obtained with SnF2 doped SnO2 thin films. Positron annihilation results showed that there are two kinds of vacancy clusters with different sizes existing in the annealed FTO thin films, and the concentration of the larger vacancy clusters of VSnO in the thin films increases with increasing SnF2 contents. Meanwhile, photoluminescence spectra results indicated that the better electrical and optical properties of the FTO thin films are attributed to FO substitutions and oxygen vacancies with higher concentration, which are supported by positron annihilation Doppler broadening results and confirmed by X-ray photoelectron spectroscopy. The results showed that widening of the optical band gap of the FTO thin films strongly depends on the carrier concentration, which is interpreted for the Burstein-Moss effect and is associated with the formation of FO and oxygen vacancies with increasing SnF2 content.

Correlated effects of fluorine and hydrogen in fluorinated tin oxide (FTO) transparent electrodes deposited by sputtering at room temperature

“…The dependence on H 2 is due to generation of oxygen vacancies by Sn 2+ in the SnO 2 mother structure. This explanation is in agreement with the reported band structure in [46] and explains small variations of energy level values as shown in Fig. 9(c), giving F O energy levels at ~0.4 eV below the CB and V O 2+ energy level at ~0.6 eV above the VB.…”

“…Alternatively, Trani et al [45] ascribed this band in SnO 2 to the appearance of a fully occupied flat energy level lying at about 1 eV above the valence band and an empty level resonant with the conduction band. Moreover, based on positron annihilation experiments, Zhou et al [46] have supported the origin of this 2.5 eV band as electron transitions from a V O + energy hybridized with the conduction band to a V O 2+ energy level.…”

“…In order to explain the effect of H 2 on the electronic structure of FTO, we have considered the reported SnO 2 and FTO band structures [46] Additionally, the intensity of the broad absorption at 400 nm (~3.1 eV) (Fig. 3 and Ref.…”

“…Fluorinated tin oxide (FTO) is a typical n-type TCM with excellent optical properties (high transmittance and wide band gap) and suitable conductivity. Among other deposition techniques, such as spray pyrolysis or pulsed laser deposition [5][6][7][8][9], sputtering has been used to prepare FTO from different starting materials as metallic Sn [10], blended SnF 2 -Sn [11], mixed oxide fluoride SnO 2 -SnF 2 [12,13]. Independently of the deposition technique, preparation at nearly room temperature is a requirement for films supported on organic substrates.…”

A hot phonon bottleneck observed upon incorporation of SnF2 to MASnI3 films and its possible role in increasing photocarrier diffusion length

“…11 Zhou et al found reduction in Sn vacancies defects in MASnI 3 solar cells, the carrier injection enhancement, and the energy bandgap widening resulting in suppressing I-V hysteresis. 12 It is challenging to obtain a stable tin-based perovskite cell with higher PCE. 13 In 2012, Chung et al first showed that the solution-processable p-type direct bandgap semiconductor CsSnI 3 can be used for hole conduction in lieu of a liquid electrolyte and the conversion efficiencies of up to 10.2% (8.51% with a mask).…”