Photoelectrochemical Screening of Solar Cell Absorber Layers: Electron Transfer Kinetics and Surface Stabilization

in Journal of Physical Chemistry. C, Nanomaterials and interfaces (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 ▲]

Crystal growth of Cu2ZnSnS4 solar cell absorber by chemical vapor transport with I2

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 ▲]

Thermodynamic Aspects of the Synthesis of Thin-Film Materials for Solar Cells

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 ▲]

Formation of Cu3BiS3 thin films via sulfurization of Bi–Cu metal precursors

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 ▲]

Formation of CuSbS2 and CuSbSe2 thin films via chalcogenisation of Sb–Cu metal precursors

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 ▲]

Cu2ZnSnSe4 thin film solar cells produced by selenisation of magnetron sputtered precursors

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