157 research outputs found
New Routes to Sustainable Materials for Photovoltaic Cells
No full textDue to the availability and low cost of the elements, the semiconductor systems Cu-Sb-Bi-S(e) and Cu-Zn-Sn-S(e) are being studied as sustainable alternatives to the expensive absorber material based on CuIn(Ga)S(e)2.
The research is focussed on two main areas:
1) Acquisition of the basic information of the ideal compounds by growth of single crystals of the solid solutions Cu2ZnSnSxSe(4-x) and CuBixSb(1-x)S2 via Chemical Vapour Transport technique.
2) Deposition of thin films of the materials by means of a variety of electrochemical techniques such as one-step electrodepositions from non aqueous solutions containing the metal precursors and elemental S, and electroplating/evaporation routes followed by annealing in S/Se rich environments.
The characterization of the properties of both single crystals and thin films of the new materials by a range of structural, electrical and photoelectrochemical techniques are being performed in order to establish their suitability as absorber layer materials for solar energy conversion. Photoactive compounds have been synthesised, with band-gap energy matching the Shockley-Queisser requirements for the efficient harvesting of solar spectrum. Further studies are now carried out in order to improve the photon to current efficiency of these materials
Synthesis of K2Se solar cell dopant in liquid NH3 by solvated electron transfer to elemental selenium
No full textThis study explores the rich chemistry of elemental selenium reduction to monoselenide anions. The simplest possible homogeneous electron transfer occurs with free electrons, which is only possible in plasmas; however, alkali metals in liquid ammonia can supply unbound electrons at much lower temperatures, allowing in situ analysis. Here, solvated electrons reduce elemental selenium to K2Se, a compound relevant for alkali metal doping of Cu(In,Ga)Se2 solar cell material. It is proposed that the reaction follows pseudo first-order kinetics with an inner-sphere or outer-sphere oxidation semi reaction mechanism depending on the concentration of solvated electrons
Synthesis, Kinetics, Characterization and Application of Sodium and Potassium (poly)Selenides for Chalcogenide Semiconductor Doping
No full textTowards a photoelectrochemical tool for comprehensive quality assessment of solar cell absorber layers
No full textBeing able to predict the optoelectronic properties of thin film solar cell by analysis of the absorber layers – i.e. before a number of deposition steps are carried out – would be a clear advantage both at academic research level and for the implementation of procedures for process monitoring in industry.
Recently we have demonstrated that the short circuit current density of CIGSe devices can be reasonably predicted by assessing photoelectrochemically the photocurrent density of the respective absorber layers on conductive substrates through a Eu3+ electrolyte junction. In such a junction the Eu3+ acts as a scavenger for the electrons generated on the p type semiconductor upon irradiation with photon whose energy is greater than the band-gap of the semiconductor.
In presence of a redox couple with suitable standard potential with respect to the semiconductor Fermi level, the junction can also be assessed in forward bias and important information can be extracted.
In this work we demonstrate that the reverse saturation current of cise solaf cell devices can be peedicteb by meeasuring ghe forward bias characteristics of the cise eu2+/3+ juncfion
The aim of this work is to identify photoelectrochemical parameters for the reliable assessment of the optoelectronic properties of thin absorber films for photovoltaic applications. The ultimate goal is to develop an on-line testing tool capable of evaluating the suitability of solar cell absorbers such as Cu(In,Ga)(S,Se)2 or Cu2ZnSn(S,Se)4 before these are processed further into complete devices by addition of n-type, window and front contact layers. This would allow monitoring the stability of part of the production plant process with inherent advantages in terms of material usage, energy and time.
By formation of virtually reversible electrolyte (Schottky) junctions [1] it is possible to interrogate semiconductor thin films and extract information about properties such as majority carrier type [2, 3], band-gap and flat-band potential [4], doping density [5], as well as insights on the presence of optically absorbing phases on the film surface [6].
In solid state devices the short circuit current density is related to the generation of carriers, their transport and their subsequent collection at the interface. This is also true for a Schottky junction.
The parallel resistance of solar cells is associated to the presence of conducting (shorting) paths; the dark current measured in solution under reversed bias should give an estimate of such paths.
The voltage of a device measured under open circuit conditions is proportional to the quasi-Fermi level splitting within the absorber. The consequence of this statement applies also to the semiconductor/electrolyte case [7].
In this work we investigate if a sound correlation between the solid state device properties (short circuit current, parallel resistance and open circuit voltage) and the corresponding parameters accessible through a transparent electrolyte junction can be established. To this end three Cu(In,Ga)Se2 absorber layers obtained by physical vapour deposition were split into two. Half were completed into solar cell devices and the other half were tested photoelectrochemically. The chosen absorber layers gave solid state device power conversion efficiencies of 6, 9 and 12.5% [8]. The photoelectrochemical experiments were performed with a three electrode setup in an equimolar solution of Eu3+/2+ and consisted of chronoamperometric and voltammetric analyses under pulsed illumination, as well as photocurrent spectroscopy.
The theoretical correlations are complicated by experimental issues including the non-ideality of surface structures and of the current collection [9]. In fact, in agreement with the literature [5, 10, 11], our work shows that photoelectrochemical assessments can also be performed in the absence of active electrolyte redox species. Nevertheless, we highlight their importance if reversibility and longtime reproducibility of the measurements are a strict requirement.
References
[1] L.M. Peter, Semiconductor Electrochemistry, in: J.M. Feliu-Martinez, V.C. Paya (Eds.) Electrochemistry, Encyclopedia of Life Support Systems, Oxford, 2010.
[2] P. Dale, A. Samantilleke, G. Zoppi, I. Forbes, S. Roncallo, L. Peter, Deposition and Characterization of Copper Chalcopyrite Based Solar Cells using Electrochemical Techniques, Electrochemical Society Transactions, 6 (2007) 535-546.
[3] J. Kessler, D. Schmid, R. Schaffler, H.W. Schock, S. Menezes, Electro-optical and photoelectrochemical studies of CuIn3Se5 chalcopyrite films, in: Photovoltaic Specialists Conference (PVSC), 1993 23rd IEEE, 1993, pp. 549 - 554.
[4] J.J. Scragg, P.J. Dale, L.M. Peter, Towards sustainable materials for solar energy conversion: Preparation and photoelectrochemical characterization of Cu2ZnSnS4, Electrochemistry Communications, 10 (2008) 639-642.
[5] D. Lincot, H. Gomez Meier, J. Kessler, J. Vedel, B. Dimmler, H.W. Schock, Photoelectrochemical study of p-type copper indium diselenide thin films for photovoltaic applications, Solar Energy Materials, 20 (1990) 67-79.
[6] D. Colombara, L.M. Peter, K. Hutchings, K.D. Rogers, S. Schäfer, J.T.R. Dufton, M.S. Islam, Formation of Cu3BiS3 thin films via sulfurization of Bi–Cu metal precursors, Thin Solid Films, 520 (2012) 5165-5171.
[7] R. Memming, Semiconductor Electrochemistry, Wiley, 2001.
[8] V. Depredurand, Y. Aida, J. Larsen, T. Eisenbarth, A. Majerus, S. Siebentritt, Surface treatment of CIS solar cells grown under Cu-excess, in: Photovoltaic Specialists Conference (PVSC), 2011 37th IEEE, 2011, pp. 000337-000342.
[9] H. Gerischer, The role of semiconductor structure and surface properties in photoelectrochemical processes, Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 150 (1983) 553-569.
[10] C. Guillen, J. Herrero, D. Lincot, Photovoltaic activity of electrodeposited p-CuInSe2/electrolyte junction, Journal of Applied Physics, 76 (1994) 359-362.
[11] O. Solorza-Feria, R. Rivera-Noriega, Photoelectrochemical response and characterization of p-CuInSe2 electrodeposited with different citrate ion concentrations, Journal of Materials Science, 30 (1995) 2616-2619.
Acknowledgements
LPV, LEM and Nexcis team members are gratefully acknowledged for help and discussion.
Prof. Laurence M. Peter is thanked for initiating the authors’ interest in Photoelectrochemistry.
The research leading to these results has received funding from the European Union’s Seventh Framework Programme FP7/2007-2013 under grant agreement no 28448
Thermochemical and kinetic aspects of the sulfurization of Cu–Sb and Cu–Bi thin films
No full textpeer reviewedCuSbS2 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.Supergen: Photovoltaic Materials for the 21st Century EP/F029624/
Revani diffusion model in Cu(In,Ga)Se2
No full textThe commercial attractiveness of Cu(In,Ga) (S,Se)(2) (CIGS) photovoltaics is still curtailed by the R&D gap that separates it from silicon. Overcoming the gap requires the pursuit of strategic approaches, leaving plenty of room for R&D at both industrial and lab scale. Yet, its technological progress hinges on our understanding of the diffusion phenomena that occur during and after the absorber growth, particularly in combination with alkali metal doping. This contribution introduces a simplified model of atomic diffusion in CIGS based on insights drawn from recent and older (but crucial) literature. The concept of anisotropy-induced fluctuations emerges. We hypothesize that grain-dependent inhomogeneities arise in CIGS devices because of crystallographic dependent alkali metal diffusivities. Numerical simulations reveal that inhomogeneous doping density and CdS buffer layer thickness may impair the device performance by up to more than 1% absolute efficiency
Unravelling the co-precipitation of spinel iron oxide nanoparticles via pH potentiometric titrations
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