In this work, we successfully demonstrated plasmonic Cu(InGa)Se2-based thin film solar cell prepared by a non-vacuum process. Cu(In,Ga)Se2, (CIGS) is a direct band gap semiconductor material that can be used as the absorption layer in thin film solar cell with the highest efficiency of 20.8 % so far. In recent years, researchers have made a lot of efforts on reducing the usage of materials in order to reduce material cost. Many possible approaches have been adopted to light absorption management to maintain cell efficiency while reducing the thickness of these absorption layers, such as nanostructured surface. Plasmonic effect, which is one of approaches for light trapping, has been successfully applied on polymer tandem solar cell and Si solar.
In the first study, Au nanoparticles (Au NPs) were introduced into CIGS/CdS and CdS/iZnO of CIGS device, respectively. Based on angle-dependent reflectance measurement, an enhanced light absorption in the range of 400~600 nm can be observed, which is consistent with the increasing external quantum efficiencies (EQE) of these devices. 8.52% enhancement of short circuit current (Jsc) and 24.7% improvement of power conversion efficiency have been attained by the light trapping effect utilizing plasmonic effect.
However, it remains challenges for applying Au NPs into Cu(InGa)Se2-based solar cells because Au NPs will react with In and Cu during high temperature annealing processes. In order to address this issue, development of thermal-stable protection shell was developed in the second study of the thesis. In brief, Au@SiO2 NPs were mixed with CuInS2 nanocrystal ink homogenously and experienced at high temperature selenization process to form CISe2 thin film layer where the plasmonic CuInSe2 (CISe2) solar cell with enhanced conversion efficiency by employing Au-SiO2 core-shell nanoparticles (Au@SiO2 NPs) can be achieved. SEM images reveal that the SiO2 shell can protect Au NPs intact after the high temperature annealing process. Consequently, under AM1.5G irradiation, the short circuit current (Jsc), open circuit voltage (Voc) and power conversion efficiency (η) have been improved by 13 %, 5 % and 17 % in average, respectively. This work successfully demonstrated enhanced light absorption scheme utilizing the Au and Au@SiO2 NPs within chalcopyrite solar cells and may have beneficial potential to other thin film photovoltaic devices systems.