Nanoparticles in Cu(In,Ga)Se2 thin film solar cells for light trapping

Abstract

Cu(In,Ga)Se2 (CIGS) solar cells have been receiving unique attention from the research and industry community, stemming mostly from the excellent electronic properties that allowed this technology to achieve record-breaking efficiency values (23.35%). However, CIGS contains scarce and expensive elements (In and Ga). Therefore, a continuous absorber layer thickness reduction is needed to allow for a large-scale deployment. However, as the absorber thickness decreases, insufficient light absorption is more evident. The work performed in this thesis tackles this topic and two novel light management architectures are studied and developed. In the first approach, a broadband External Quantum Efficiency enhancement and a 3.28 mA/cm2 short circuit current increase are obtained with the introduction of Au nanoparticle aggregates at the solar cell rear contact. This improvement might be attributed to two factors: the top surface roughness introduced by the Au aggregates and a rear contact diffuse reflection increase, as demonstrated through optical simulations. The second approach consisted on optimizing the deposition of individual Au nanoparticles monolayers, to take advantage of the high scattering cross-section that the nanoparticles present at their resonant frequency. The deposition of individual nanoparticles with a minimal presence of aggregates is demonstrated.