Single-crystal Cu(In,Ga)Se₂solar cells grown on GaAs substrates

Abstract

Single-crystal Cu(In,Ga)Se2 (CIGS) solar cells were produced with techniques developed for high-efficiency polycrystalline CIGS solar cells. The CIGS layers of a lattice match with GaAs were grown on GaAs(001) substrates by co-evaporation. The presence of a single-crystal CIGS layer without dislocations was confirmed by transmission electron microscopy. Alkaline metal incorporations were achieved by doping and postdeposition treatments. Ga grading structures were fabricated by two-layer deposition with different Ga contents. The Ga grading significantly increased the fill factor and open-circuit voltage. The best efficiency of 20% was achieved after heat–light soaking.

Surface characterization of epitaxial Cu-rich CuInSe2 absorbers

“…1a) revealed trenches aligned in the [011] direction (cubic system) of the GaAs substrate with peak-to-peak height of up to 130 nm. Such patterns were already demonstrated for CIGS samples, where we can associate the alignment to the preferential growth direction during the epitaxial process and the facets to the spontaneous formation of a low energetic (112) polar surface [4], [15], [16]. Fig.…”

“…Almost all absorbers and cells have been grown on glass substrates with a Mo back contact, which leads to a polycrystalline growth with many grain boundaries and different surface orientations of the individual grains [2], [3]. Only recently solar cells based on epitaxially grown of CIGS deposited on GaAs wafers have achieved an efficiency of 20% [4]. One of the main advantages of high quality single crystalline material is the absence of grain boundaries, leading to higher values of quasi-Fermi level splitting due to the reduction of carrier recombination sites [5].…”

Quantifying Large Lattice Relaxations in Photovoltaic Devices

“…Typically, the net acceptor (hole) concen- * marcon@bgsu.edu tration, N , and open-circuit voltage, V oc , increase with temperature under charge injection conditions, whereas dark annealing (without charge injection) tends to reduce N and V oc . Similar effects have been observed in single crystal CIGS PV devices [18].…”

The fox and the hound: in-depth and in-grain Na doping and Ga grading in Cu(In,Ga)Se2 solar cells

“…Since record cells are historically polycrystalline in nature, the study is easily referred to as irrelevant for the technology. However, besides the fact that monocrystalline CIGS cells have now reached notable efficiencies up to 20%, 75 the ndings must be related to the broader context if the community aspires to gain a deeper understanding of the fundamental material properties.…”