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See detailDeliberate and Accidental Gas-Phase Alkali Doping of Chalcogenide Semiconductors: Cu(In,Ga)Se2
Colombara, Diego UL; Berner, Ulrich; Ciccioli, Andrea et al

in Scientific Reports (2017), 7

Alkali metal doping is essential to achieve highly efficient energy conversion in Cu(In,Ga)Se2 (CIGSe) solar cells. Doping is normally achieved through solid state reactions, but recent observations of ... [more ▼]

Alkali metal doping is essential to achieve highly efficient energy conversion in Cu(In,Ga)Se2 (CIGSe) solar cells. Doping is normally achieved through solid state reactions, but recent observations of gas phase alkali transport in the kesterite sulfide (Cu2ZnSnS4) system (re)open the way to a novel gas-phase doping strategy. However, the current understanding of gas-phase alkali transport is very limited. This work (i) shows that CIGSe device efficiency can be improved from 2% to 8% by gas-phase sodium incorporation alone, (ii) identifies the most likely routes for gas-phase alkali transport based on mass spectrometric studies, (iii) provides thermochemical computations to rationalize the observations and (iv) critically discusses the subject literature with the aim to better understand the chemical basis of the phenomenon. These results suggest that accidental alkali metal doping occurs all the time, that a controlled vapor pressure of alkali metal could be applied during growth to dope the semiconductor, and that it may have to be accounted for during the currently used solid state doping routes. It is concluded that alkali gas-phase transport occurs through a plurality of routes and cannot be attributed to one single source. [less ▲]

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See detailA new phase in the Cu–Sn–Zn–S photovoltaic system
Boero, Federica; Delsante, Simona; Colombara, Diego UL et al

in Materials Letters (2015), 145

More than 35 samples of the Cu–Zn–Sn–S system were prepared along the ZnS–Cu2SnS3 section, in order to study the bulk properties of the Cu2ZnSnS4 semiconductor. During the investigation of these samples ... [more ▼]

More than 35 samples of the Cu–Zn–Sn–S system were prepared along the ZnS–Cu2SnS3 section, in order to study the bulk properties of the Cu2ZnSnS4 semiconductor. During the investigation of these samples, a new quaternary phase was detected by Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM/EDS) analyses. The results indicate that the new phase has a range of solubility corresponding to Cu(2-2x)Zn(6+3x)Sn(1-x)S9 with 0 < x < 0.74 and decomposes at 790 °C as determined by Differential Thermal Analysis (DTA). [less ▲]

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See detailCrystal growth of Cu2ZnSnS4 solar cell absorber by chemical vapor transport with I2
Colombara, Diego UL; Delsante, Simona; Borzone, Gabriella et al

in Journal of Crystal Growth (2013), 364

Single crystals of Cu2ZnSnS4 have been produced within sealed quartz ampoules via the chemical vapour transport technique using I2 as the transporting agent. The effects of temperature gradient and I2 ... [more ▼]

Single crystals of Cu2ZnSnS4 have been produced within sealed quartz ampoules via the chemical vapour transport technique using I2 as the transporting agent. The effects of temperature gradient and I2 load on the crystal habit and composition are considered. Crystals have been analyzed with XRD, SEM, and TEM for compositional and structural uniformities at both microscopic and nanoscopic levels. The synthesized crystals have suitable (I2-load dependent) properties and are useful for further solar absorber structural and physical characterizations. A new chemical vapour transport method based on longitudinally isothermal treatments is attempted. Based on a proposed simplistic mechanism of crystal growth, conditions for crystal enlargement with the new method are envisaged. [less ▲]

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