Cu2SnS3 based thin film solar cells from chemical spray pyrolysis

in Thin Solid Films (2019), 669

Synthesis, theoretical and experimental characterisation of thin film Cu2Sn1-xGexS3 ternary alloys (x = 0 to 1): Homogeneous intermixing of Sn and Ge

in Acta Materialia (2018), 151

Cu2Sn1-xGexS3 is a p-type semiconductor alloy currently investigated for use as an absorber layer in thin film solar cells. The aim of this study is to investigate the properties of this alloy in thin ... [more ▼]

Cu2Sn1-xGexS3 is a p-type semiconductor alloy currently investigated for use as an absorber layer in thin film solar cells. The aim of this study is to investigate the properties of this alloy in thin film form in order to establish relationships between group IV composition and structural, vibrational and opto-electronic properties. Seven single phase Cu2Sn1-xGexS3 films are prepared from x ¼ 0 to 1, showing a uniform distribution of Ge and Sn laterally and in depth. The films all show a monoclinic crystal structure. The lattice parameters are extracted using Le Bail refinement and show a linear decrease with increasing Ge content. Using density-functional theory with hybrid functionals, we calculate the Raman active phonon frequencies of Cu2SnS3 and Cu2GeS3. For the alloyed compounds, we use a virtual atom approximation. The shift of the main Raman peak from x ¼ 0 to x ¼ 1 can be explained as being half due to the change in atomic masses and half being due to the different bond strength. The bandgaps of the alloys are extracted from photoluminescence measurements and increase linearly from about 0.90 to 1.56 eV with increasing Ge. The net acceptor density of all films is around 1018 cm 3. These analyses have established that the alloy forms a solid solution over the entire composition range meaning that intentional band gap grading should be possible for future absorber layers. The linear variation of the unit cell parameters and the band gap with group IV content allows composition determination by scattering or optical measurements. Further research is required to reduce the doping density by two orders of magnitude in order to improve the current collection within a solar cell device structure. [less ▲]

Sodium enhances indium-gallium interdiffusion in copper indium gallium diselenide photovoltaic absorbers

in Nature Communications (2018)

Deliberate and Accidental Gas-Phase Alkali Doping of Chalcogenide Semiconductors: Cu(In,Ga)Se2

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 ▲]

Valence band splitting in Cu2(Sn,Ge, Si)S3: effect on optical absorption spectra

in Physica Status Solidi. Rapid Research Letters (2017)

We perform a detailed analysis of the valence band splitting (VBS) effect on the absorption spectra of monoclinic Cu2(Sn,Ge,Si)S3 combining theory and experiment. We cal- culate the imaginary part of the ... [more ▼]

We perform a detailed analysis of the valence band splitting (VBS) effect on the absorption spectra of monoclinic Cu2(Sn,Ge,Si)S3 combining theory and experiment. We cal- culate the imaginary part of the dielectric function for all three compounds using hybrid functionals and maximally lo- calized Wannier functions in remarkably dense k-meshes to ensure an accurate description of the low energy spectral regime. We find that the VBS will affect the absorption spectra of these materials leading to multiple absorption onsets. Our experimental spectra on Cu2(Sn,Ge)S3, analysed using both Tauc plots and inflection points, verify this prediction. A good agreement between theory and experiment in terms of VBS values is recorded. [less ▲]

Nanometre-scale optical property fluctuations in Cu2ZnSnS4 revealed by low temperature cathodoluminescence

in Solar Energy Materials & Solar Cells (2017), 174

Electrodeposition of germanium-containing precursors for Cu2(Sn,Ge)S3 thin film solar cells

in Electrochimica Acta (2017)

Crystallographic and optoelectronic properties of the novel thin film absorber Cu2GeS3

in Proceedings of SPIE (2016, September)

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

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 ▲]

Electrodeposition and selenization of brass/tin/germanium multilayers for Cu2Zn(Sn1-xGex)Se4 thin film photovoltaic devices

in Electrochimica Acta (2016), 198