Ab initioelectronic structure calculations for metallic intermediate band formation in photovoltaic materials

Abstract

A metallic isolated band in the middle of the band gap of several III-V semiconductors has been predicted as photovoltaic materials with the possibility of providing substantially enhanced efficiencies. We have investigated the electronic band structures and lattice constants of Ga n As m M and Ga n P m M with MϭSc, Ti, V, and Cr, to identify whether this isolated band is likely to exist by means of accurate calculations. For this task, we use the SIESTA program, an ab initio periodic density-functional method, fully self consistent in the localdensity approximation. Norm-conserving, nonlocal pseudopotentials and confined linear combination of atomic orbitals have been used. We have carried out a case study of Ga n As m Ti and Ga n P m Ti energy-band structure including analyses of the effect of the basis set, fine k-point mesh to ensure numerical convergence, structural parameters, and generalized gradient approximation for exchange and correlation corrections. We find the isolated intermediate band when one Ti atom replaces the position of one As ͑or P͒ atom in the crystal structure. For this kind of compound we show that the intermediate band relative position inside the band gap and width are sensitive to the dynamic relaxation of the crystal and the size of the basis set.

The Intermediate Band Solar Cell: Progress Toward the Realization of an Attractive Concept

“…Since 2002, ab initio band calculations in our group have suggested that certain transition metals could form an IB in III-V [75] compounds. More recently, V-added In 2 S 3 with high concentration of V (V 2 In 14 S 2 4) has been prepared by solvo-thermal synthesis.…”

Intermediate band position modulated by Zn addition in Ti doped CuGaS2

“…In our group, we have proposed some transition metal doped semiconductors (TMS) [6][7][8][9] as intermediate band materials. These earlier works [8,9] have revealed that the insertion of Ti into a chalcopyrite semiconductor such as CuGaS 2 , with a band-gap found experimentally as 2.53 eV [10] depicts a separated intermediate band.…”

Light intensity enhancement by diffracting structures in solar cells

“…Furthermore, certain solar cell types and, in particular, the intermediate band solar cells 1 ͑IBSCs͒-in which electron-hole pairs are created out of sub-band-gap photons by means of quantum dots 2 ͑QDs͒ or by alloys of different types [3][4][5] -absorb weakly the sub-band-gap photons because of the low density of absorbing centers ͑below 10 17 cm −3 in the QD-IBSC͒. It is to be noted that most probably QD-IBSC will not be practical unless they can utilize a good scheme of light-absorption intensification.…”