Metal-oxide broken-gap tunnel junction for copper indium gallium diselenide tandem solar cells

Abstract

A metal-oxide broken-gap heterojunction between p-Cu 2 O and n-In 2 O 3 is proposed and studied for use as a tunnel junction in polycrystalline CuIn 1-x Ga x Se 2 (CIGS) based tandem solar cells using numerical device simulation. Specifically, a tandem solar cell with a CuGaSe 2 (CGS) absorber top cell and a CuInSe 2 (CIS) absorber bottom cell was considered. The ballistic transport model explains well the carrier transport in the broken-gap heterojunction. Broken-gap heterojunctions provide linear current-voltage characteristics even if one side is lightly doped and the junction resistance is much lower than typical values of series resistance in solar cells. However, electron affinities of metal oxides for broken-gap band alignment may induce an energy barrier between the tunnel junction and the top and bottom solar cells, degrading performance. These barriers can be reduced using buffer layers. For example, NiO and graded In 2 O 3-ZnO buffer layers are proposed beneath CGS top solar cell and above the CIS bottom solar cell, respectively. With these buffer layers, the efficiencies of the top and bottom cells are 17.5% and 6.5% respectively. The modeled efficiency of the CGS/CIS tandem solar cell is 24.1% and there is virtually no significant efficiency loss due to the presence of the broken-gap junction.

Semiconductor Electrode Materials Applied in Photoelectrocatalytic Wastewater Treatment—an Overview

“…In the case of the type III heterojunction, the band gaps of two semiconductor do not overlap and the migration of electrons and holes between two semiconductors does not occur. However, the charge transfer between semiconductors is possible due to broken gap alignment with increasing overall voltage [179,180]. Such heterojunction is unsuitable for the enhancement of photogenerated electrons and holes separation.…”

Electronic properties of the Sn1−xPbxO alloy and band alignment of the SnO/PbO system: a DFT study

“…3 meaning that a high crystal quality heterojunction interface is feasible. This could be used as a p-n tunnel junction in tandem solar cells consisting of multiple layers of Sn 1−x Pb x O with different energy band gaps modified by x similar to the Cu 2 O/In 2 O 3 tunnel junction used in copper indium gallium diselenide tandem solar cells by Song et al 39 . In addition to solar cells the properties of Sn 1−x Pb x O ternary oxide and SnO/PbO heterojunction would also be very interesting for the efficient separation of photo excited electron–hole pairs during the photo-electro-chemical generation of oxygen and hydrogen i.e.…”

“…In the 226 supercell that we examine here, the Sn-poor SnO and Pb-rich PbO are calculated with a vacancy of an atomic concentration of 2.08%. The band alignment of the energy levels 39 . In addition to solar cells the properties of Sn 1−x Pb x O ternary oxide and SnO/PbO heterojunction would also be very interesting for the efficient separation of photo excited electron-hole pairs during the photoelectro-chemical generation of oxygen and hydrogen i.e.…”

Sputtering of metal oxide tunnel junctions for tandem solar cells

“…As a result, the junction is ohmic in either direction. Song et al performed numerical simulations of a metal-oxide broken-gap heterojunction between p-Cu 2 O and n-In 2 O 3 [6]. Their results suggest that low-resistance can be achieved for moderate doping concentrations and that conduction in the depletion region of the junction occurs by ballistic transport.…”

“…Of the thin film PV technologies currently in production, CIGS has the highest efficiency. A tandem cell of CIAGS/CIGS has been proposed which gives a substantially higher theoretical efficiency (~24%) [6] given existing material properties and processing.…”