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See detailOptoelectronic and Spectroscopic Characterization of Vapour-Transport Grown Cu2ZnSnS4 Single Crystals
Tat Ming Ng; Weller, Mark T.; Kissling, Gabriela P. et al

in Journal of Materials Chemistry A (2017)

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See detailPhotoelectrochemical Screening of Solar Cell Absorber Layers: Electron Transfer Kinetics and Surface Stabilization
Colombara, Diego UL; Dale, Phillip UL; Kissling, Gabriela P. et al

in Journal of Physical Chemistry C (2016)

edox electrolyte contacts offer a simple way of testing the photocurrent generation/collection efficiency in partially completed thin-film solar cells without the need to complete the entire fabrication ... [more ▼]

edox electrolyte contacts offer a simple way of testing the photocurrent generation/collection efficiency in partially completed thin-film solar cells without the need to complete the entire fabrication process. However, the development of a reliable quantitative method can be complicated by the instability of the semiconductor/electrolyte interface. In the case of Cu(In,Ga)Se2 (CIGSe) solar cells, these problems can be overcome by using samples that have undergone the next processing step in solar cell fabrication, which involves chemical bath deposition of a thin (ca. 50 nm) CdS buffer layer. The choice of redox system is also critical. The frequently used Eu3+/2+ redox couple is not suitable for reliable performance predictions since it suffers from very slow electron transfer kinetics. This leads to the buildup of photogenerated electrons near the interface, resulting in electron–hole recombination. This effect, which can be seen in the transient photocurrent response, has been quantified using intensity-modulated photocurrent spectroscopy (IMPS). The study has demonstrated that the more oxidizing Fe(CN)63–/4– redox system can be used when a CdS buffer layer is deposited on the CIGSe absorber. The wide bandgap CdS acts as a barrier to hole injection, preventing decomposition of the CIGSe and formation of surface recombination centers. The IMPS response of this system shows that there is no recombination; i.e., electron scavenging is very rapid. It is shown that measurements of the external quantum efficiency made using the Fe(CN)63–/4– redox couple with CdS-coated CIGSe layers can provide reliable predictions of the short-circuit currents of the complete solar cells. Similar results have been obtained using CdS-coated GaAs layers, suggesting that the new approach may be widely applicable. [less ▲]

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See detailSynthesis, Characterization, and Electronic Structure of Single-Crystal SnS, Sn2S3, and SnS2
Burton, Lee A.; Colombara, Diego UL; Abellon, Ruben D. et al

in Chemistry of Materials (2013), 25(24), 4908-4916

Tin sulfide is being widely investigated as an earth-abundant light harvesting material, but recorded efficiencies for SnS fall far below theoretical limits. We describe the synthesis and characterization ... [more ▼]

Tin sulfide is being widely investigated as an earth-abundant light harvesting material, but recorded efficiencies for SnS fall far below theoretical limits. We describe the synthesis and characterization of the single-crystal tin sulfides (SnS, SnS2, and Sn2S3) through chemical vapor transport, and combine electronic structure calculations with time-resolved microwave conductivity measurements to shed light on the underlying electrical properties of each material. We show that the coexistence of the Sn(II) and Sn(IV) oxidation states would limit the performance of SnS in photovoltaic devices due to the valence band alignment of the respective phases and the ''asymmetry'' in the underlying point defect behavior. Furthermore, our results suggest that Sn2S3, in addition to SnS, is a candidate material for low-cost thin-film solar cells. [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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See detailRocking disc electro-deposition of CuIn alloys, selenisation, and pinhole effect minimisation in CISe solar absorber layers
Cummings, Charles Y.; Zoppi, Guillaume; Forbes, Ian et al

in Electrochimica Acta (2012), 79

The co-electrodeposition of copper and indium from a pH 3 tartrate bath onto 4.8 cm × 2.5 cm Mo and MoSe2 substrates is studied and conditions are optimised for CuIn alloy films. Selenisation at ca. 500 ... [more ▼]

The co-electrodeposition of copper and indium from a pH 3 tartrate bath onto 4.8 cm × 2.5 cm Mo and MoSe2 substrates is studied and conditions are optimised for CuIn alloy films. Selenisation at ca. 500 °C for 30 min in selenium vapour gives CuInSe2 (or CISe). Mapping using the photo-electrochemical reduction of Eu(NO3)3 is used to asses the relative photoactivity as a function of position and surface treatment.Etching of detrimental CuxSe phases is investigated with 5% and 0.5% (w/w) aqueous KCN. The slower 0.5% (w/w) KCN etch allows better process control, and re-annealing at 500 °C for 30 min followed by further etching significantly improved the photo-activity. However, over the large area local pinhole recombination effects are substantial. An alternative low temperature film optimisation method is proposed based on (i) KCN over-etch, (ii) hypochlorite (5%, w/w) pinhole removal (Mo etch), and (iii) a final KCN etch to give good and more uniform activity. [less ▲]

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See detailThermodynamic Aspects of the Synthesis of Thin-Film Materials for Solar Cells
Scragg, Jonathan J.; Dale, Phillip UL; Colombara, Diego UL et al

in Chemphyschem : A European Journal of Chemical Physics and Physical Chemistry (2012), 13(12), 30353046

A simple and useful thermodynamic approach to the prediction of reactions taking place during thermal treatment of layers of multinary semiconductor compounds on different substrates has been developed ... [more ▼]

A simple and useful thermodynamic approach to the prediction of reactions taking place during thermal treatment of layers of multinary semiconductor compounds on different substrates has been developed. The method, which uses the extensive information for the possible binary compounds to assess the stability of multinary phases, is illustrated with the examples of Cu(In,Ga)Se2 and Cu2ZnSnSe4 as well as other less-studied ternary and quaternary semiconductors that have the potential for use as absorbers in photovoltaic devices. [less ▲]

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See detailFormation of Cu3BiS3 thin films via sulfurization of Bi–Cu metal precursors
Colombara, Diego UL; Peter, Laurence M.; Hutchings, Kyle et al

in Thin Solid Films (2012), 520(16), 51655171

Thin films of Cu3BiS3 have been produced by conversion of stacked and co-electroplated Bi–Cu metal precursors in the presence of elemental sulfur vapor. The roles of sulfurization temperature and heating ... [more ▼]

Thin films of Cu3BiS3 have been produced by conversion of stacked and co-electroplated Bi–Cu metal precursors in the presence of elemental sulfur vapor. The roles of sulfurization temperature and heating rate in achieving single-phase good quality layers have been explored. The potential loss of Bi during the treatments has been investigated, and no appreciable compositional difference was found between films sulfurized at 550 °C for up to 16 h. The structural, morphological and photoelectrochemical properties of the layers were investigated in order to evaluate the potentials of the compound for application in thin film photovoltaics. [less ▲]

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See detailStructural and electronic properties of CuSbS2 and CuBiS2: potential absorber materials for thin-film solar cells
Dufton, Jesse T.R.; Walsh, Aron; Panchmatia, Pooja M. et al

in Physical Chemistry Chemical Physics [=PCCP] (2012), 14(20), 7229-7233

As the demand for photovoltaics rapidly increases, there is a pressing need for the identification of new visible light absorbing materials for thin-film solar cells that offer similar performance to the ... [more ▼]

As the demand for photovoltaics rapidly increases, there is a pressing need for the identification of new visible light absorbing materials for thin-film solar cells that offer similar performance to the current technologies based on CdTe and Cu(In,Ga)Se2. Metal sulphides are the ideal candidate materials, but their band gaps are usually too large to absorb significant fractions of visible light. However, by combining Cu+ (low binding energy d10 band) and Sb3+/Bi3+ (low binding energy s2 band), the ternary sulphides CuSbS2 and CuBiS2 are formed, which have been gathering recent interest for solar cell applications. Using a hybrid density functional theory approach, we calculate the structural and electronic properties of these two materials. Our results highlight the stereochemical activity of the Sb and Bi lone pair electrons, and predict that the formation of hole carriers will occur in the Cu d10 band and hence will involve oxidation of Cu(I). [less ▲]

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See detailThermochemical and kinetic aspects of the sulfurization of Cu–Sb and Cu–Bi thin films
Colombara, Diego UL; Peter, Laurence M.; Rogers, Keith D. et al

in Journal of Solid State Chemistry (2011)

CuSbS2 and Cu3BiS3 are being investigated as part of a search for new absorber materials for photovoltaic devices. Thin films of these chalcogenides were produced by conversion of stacked and co ... [more ▼]

CuSbS2 and Cu3BiS3 are being investigated as part of a search for new absorber materials for photovoltaic devices. Thin films of these chalcogenides were produced by conversion of stacked and co-electroplated metal precursor layers in the presence of elemental sulfur vapour. Ex-situ XRD and SEM/EDS analyses of the processed samples were employed to study the reaction sequence with the aim of achieving compact layer morphologies. A new “Time-Temperature-Reaction” (TTR) diagram and modified Pilling–Bedworth coefficients have been introduced for the description and interpretation of the reaction kinetics. For equal processing times, the minimum temperature required for CuSbS2 to appear is substantially lower than for Cu3BiS3, suggesting that interdiffusion across the interfaces between the binary sulfides is a key step in the formation of the ternary compounds. The effects of the heating rate and sulfur partial pressure on the phase evolution as well as the potential losses of Sb and Bi during the processes have been investigated experimentally and the results related to the equilibrium pressure diagrams obtained via thermochemical computation. [less ▲]

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See detailFormation of CuSbS2 and CuSbSe2 thin films via chalcogenisation of Sb–Cu metal precursors
Colombara, Diego UL; Peter, Laurence M.; Rogers, Keith D. et al

in Thin Solid Films (2011), 519(21), 74387443

Due to the availability and low cost of the elements, the ternary Cu–Sb–S and Cu–Sb–Se semiconductor systems are being studied as sustainable alternative absorber materials to replace CuIn(Ga)(S,Se)2 in ... [more ▼]

Due to the availability and low cost of the elements, the ternary Cu–Sb–S and Cu–Sb–Se semiconductor systems are being studied as sustainable alternative absorber materials to replace CuIn(Ga)(S,Se)2 in thin film photovoltaic applications. Simple evaporation of the metal precursors followed by annealing in a chalcogen environment has been employed in order to test the feasibility of converting stacked metallic layers into the desired compounds. Other samples have been produced from aqueous solutions by electrochemical methods that may be suitable for scale-up. It was found that the minimum temperature required for the complete conversion of the precursors into the ternary chalcogen is 350 °C, while binary phase separation occurs at lower temperatures. The new materials have been characterised by structural, electrical and photoelectrochemical techniques in order to establish their potential as absorber layer materials for photovoltaic applications. The photoactive films consisting of CuSbS2 and CuSbSe2 exhibit band-gap energies of ~ 1.5 eV and ~ 1.2 eV respectively, fulfilling the Shockley–Queisser requirements for the efficient harvesting of the solar spectrum. [less ▲]

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See detailSynthesis and characterization of Cu2ZnSnS4 absorber layers by an electrdeposition-annealing route
Scragg, Jonathan J.; Dale, Phillip UL; Peter, Laurence M.

in Thin Solid Films (2009), 517(7), 2481-2484

An electrodeposition-annealing route to films of the promising p-type absorber material Cu2ZnSnS4 (CZTS) using layered metal precursors is studied. The dependence of device performance on composition is ... [more ▼]

An electrodeposition-annealing route to films of the promising p-type absorber material Cu2ZnSnS4 (CZTS) using layered metal precursors is studied. The dependence of device performance on composition is investigated, and it is shown that a considerable Cu-deficiency is desirable to produce effective material, as measured by photoelectrochemical measurements employing the Eu3+/2+ redox couple. The differing effects of using elemental sulphur and H2S as sulphur sources during annealing are also studied, and it is demonstrated that H2S annealing results in films with improved crystallinity. [less ▲]

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See detailCu2ZnSnSe4 thin film solar cells produced by selenisation of magnetron sputtered precursors
Zoppi, Guillaume; Forbes, Ian; Miles, Robert W. et al

in Progress in Photovoltaics (2009), 17(5), 315-319

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