Infuence of absorber thickness on Cu(In,Ga)Se2 solar cells with different buffer layers
(English)Manuscript (preprint) (Other academic)
The purpose of this work is to investigate the interplay between the absorber layer of Cu(In,Ga)Se2 solar cells and the contacts, including the buﬀer layer, of these devices. With this in mind Cu(In,Ga)Se2 devices with gallium-graded absorber layers of diﬀerent thicknesses and different types of buffer layers are fabricated. Absorbers are co-evaporated in-line with the substrate speed determining the layer thickness. Absorber layers and ﬁnished devices are characterized. Voc and FF optima are found for cells with 0.8 µm to 0.9 µm thick absorber layers but the highest efficiencies are found for standard devices with 1.6 µm absorbers due to a high Jsc. Cu(In,Ga)Se2 cells with Zn(O,S) buffer layers are found to be more efficient than CdS reference devices for the same absorber thickness due to a higher Jsc caused mainly by less light absorption in the alternative buﬀer layer. For cells with absorber layers thinner than normal, a better QE was also observed at longer wavelengths. Electrical simulations are used to reproduce the behaviour of the devices. It is found that recombination at the back contact limits the thinner devices with CdS buffer layers while the thin Zn(O,S) devices also have a problem with interface recombination. These recombination paths are over-shadowed in the standard thick devices by recombination in the CIGS layer.
Solar cells, CIGS, Alternative buffer layers, Electrical modelling
Other Electrical Engineering, Electronic Engineering, Information Engineering Materials Engineering
Research subject Engineering Science with specialization in Electronics
IdentifiersURN: urn:nbn:se:uu:diva-168615OAI: oai:DiVA.org:uu-168615DiVA: diva2:500457