New Materials for Intermediate Band Photovoltaic Cells. Theoretical and Experimental Approaches (original) (raw)
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Towards an ab-initio characterization of novel intermediate band photovoltaic materials
2008 Conference on Optoelectronic and Microelectronic Materials and Devices, 2008
An ab-initio study of novel photovoltaic materials with enhanced optoelectronic properties is presented in this contribution. Predictions of absorption coefficients agree completely with the characterization of the first experimental samples grown in the laboratory. Compounds selected for the study are derived from chalcogenide semiconductors in which several atoms are substituted by transition elements. These atoms modify the electronic band structure in such a way that a new narrow band appears inside the parent semiconductor band-gap. Partial occupation of this band enables that additional carriers could be obtained from absorption of photons with energy lower than that of the band-gap, thus enhancing the photovoltaic conversion properties of the material. It was estimated than a photovoltaic solar cell designed from this novel concept could reach a thermodynamic efficiency of 63.2% compared to 43.1% corresponding to the thermodynamic efficiency limit of conventional semiconductor based solar cells. Results show a significant enhancement of the absorption coefficient respecting to the corresponding parent semiconductor in the main emission region of the solar spectrum. For some of the theoretically proposed compounds, optoelectronic properties of recently synthesized samples have been obtained experimentally. Comparison of experimental absorption measurements with results of the calculations presented here shows a very good agreement.
Thin Solid Films, 2007
Electronic structure calculations are carried out for CuGaS 2 partially substituted with Ti, V, Cr or Mn to ascertain if some of these systems could provide an intermediate band material able to give a high efficiency photovoltaic cell. Trends in electronic level positions are analyzed and more accurate advanced theory levels (exact exchange or Hubbard-type methods) are used in some cases. The Ti-substituted system seems more likely to yield an intermediate band material with the desired properties, and furthermore seems realizable from the thermodynamic point of view, while those with Cr and Mn might give half-metal structures with applications in spintronics.
Chemistry of Materials, 2008
Current photovoltaic (PV) devices and photocatalysts can use solar light through a process in which the absorption of one photon by a semiconductor leads in the latter to the promotion of an electron from the valence band (VB) to the conduction band (CB) with the subsequent production of electric current or chemical reactions. Within this mechanism, photons with energy lower than the forbidden band gap width E g cannot be used. In recent years it has been proposed 1 that the insertion of an additional level (the intermediate band, IB) in the forbidden gap could provide an additional path for attaining the same final excitation result through the absorption of two photons with energy lower than E g , similarly to what happens in natural photosynthesis ( ). Photogenerated holes and electrons are then extracted from the VB and CB at the corresponding electron potential: in a photovoltaic cell, with electrical contacts (thick black lines in ) having proper Fermi levels, and in photocatalysis, via transfer to adsorbed molecules having proper redox states, driving chemical reactions.
Thin-film intermediate band chalcopyrite solar cells
Thin Solid Films, 2009
The feasibility of implementing the intermediate-band (IB) concept into a relevant thin-film technology has been assessed. Compounds belonging to the group of I-III-VI2 chalcopyrites, currently used as absorbers in the leading thin-film technology, appear as promising candidates for the realization of IB-devices. In this paper we first analyze the expected performance of such a thin-film intermedíate band solar cell (TF-IBSC) by considering different levéis of idealization. In the second part of the paper some issues relevant for the practical realization of IBs in chalcopyrites are discussed and impurities acting as potential IB-precursors in the chalcopyrite sulfide host identified.
ASEPE-2013
One possible way for enhancing the efficiency of photovoltaic (PV) cells is the use of materials with more than one band gap. In the intermediate band gap solar cell (IBSC) an intermediate narrow metallic band (IB) is placed in the traditional forbidden band gap which can extend absorption region. This generates extra electron–hole pairs and thus increases the current without decreasing the output voltage and therefore increases the quantum efficiency. Substitution of transition metal atoms (TM) in the 3C-SiC may give rise to a type of high-efficiency photovoltaic materials with intermediate bands to absorb low energy photons. In the present study comprehensive analysis is carried out on this kind of materials. Theoretical studies confirm the formation of suitable mini-bands within 3C-SiC band gap by doping of transition metals in 3C-SiC crystal structure. The mini bands mainly are created by 3d orbitals of the transition metals. Absorption coefficient, density of states and band structure are three important features of the proposed materials. Here, we calculated these characteristics for the 3C-SiC doped with TM=Fe as candidates for presenting an isolated partially-filled narrow bands between the valance band and the conduction band of 3C-SiC. The results show that a Fe3+ doped3C-SiC is a good candidate for high efficiency solar cell.
Properties of Novel Non-Silicon Materials for Photovoltaic Applications: A First-Principle Insight
Materials, 2018
Due to the low absorption coefficients of crystalline silicon-based solar cells, researchers have focused on non-silicon semiconductors with direct band gaps for the development of novel photovoltaic devices. In this study, we use density functional theory to model the electronic structure of a large database of candidates to identify materials with ideal properties for photovoltaic applications. The first screening is operated at the GGA level to select only materials with a sufficiently small direct band gap. We extracted twenty-seven candidates from an initial population of thousands, exhibiting GGA band gap in the range 0.5–1 eV. More accurate calculations using a hybrid functional were performed on this subset. Based on this, we present a detailed first-principle investigation of the four optimal compounds, namely, TlBiS2, Ba3BiN, Ag2BaS2, and ZrSO. The direct band gap of these materials is between 1.1 and 2.26 eV. In the visible region, the absorption peaks that appear in the ...
Thin Solid Films, 2008
The optical properties of a novel potential high-efficiency photovoltaic material have been studied. This material is based on a chalcopyritetype semiconductor (CuGaSa) with some Ga atom substituted by Ti and is characterized by the formation of an isolated transition-metal band between the valence band and the conduction band. We present a study in which ab-initio density functional theory calculations within the generalized gradient approximation are carried out to determine the optical reflectivity and absorption coefficient of the materials of interest. Calculations for the host semiconductor are in good agreement with experimental results within the limitations of the approach. We find, as desired, that because of the intermediate band, the new Ti-substituted material would be able to absorb photons of energy lower than the band-gap of the host chalcopyrite. We also analyze the partial contributions to the main peaks of its spectrum.
Solar Energy Materials and Solar Cells, 2010
We present absorption properties enhancement for two CuGaS2-based intermediate-band materials, as promising compounds for high efficiency, lower-cost photovoltaic devices. Previous band diagrams calculations predicted that these materials present a partially filled localized band within the band gap of the host semiconductor, which would increase the absorption of low-energy photons, creating additional electron-hole pairs respect to a conventional semiconductor. This could ideally result in an increase of the photocurrent of the cell without the fall of the open-circuit voltage. In this paper we show, using density functional methods, the effect of this intermediate band on the optical properties of the derived alloys. We highlight the significant enhancement of the absorption coefficient observed in the most intense range of the solar emission and we study the reflectance and transmittance properties of the materials in order to understand the effect of the thickness of the sample on the optical properties. We compare two different substituents of the Ga atoms in CuGaS 2 , namely, Ti and Cr atoms, able to form the intermediate-band material, and their interest for photovoltaic applications.