Mechanism Of Surface Plasmon Enhancement In Organic/Hybrid Solar Cells With Ag Nanostructures

With the introduction of Ag nanostructures with surface plasmon, the light absorption and power efficiency will be increased in solar cells. Compared with other metals, Ag nanostructures are easily prepared, more resistive againist degragation and exhibit high absorption coefficients due to the strong localized plasmonic resonance. This report demonstrates the influence on surface plasmon by changing the shape, morphology and surrounding environment of Ag nanostructures. The organic solar cell and hybrid solar cell were fabricated with Ag nanostructures to improve the light absorption and power efficiency. The main achievements pertained are summarized as follow:Firstly, we demonstrated plasmonic mechanisms and effects by introducing Ag nanoprisms(Ag NPs) in polymer solar cells with a structure of ITO/Ag NPs/PEDOT: PSS/P3HT: PCBM/Li F/Al to improve the light absorption and performance. By changing the size and morphology of Ag NPs, different plasmonic resonance characteristics can be obtained. The device with good spectral overlap between Ag NPs SPRs and active layer exhibits the highest photocurrent. The influence of electromagnetic field of Ag NPs in the polymer solar cell has been further investigated by changing the thickness of the PEDOT: PSS buffer layer. It can be found that there will be more local electromagnetic near-fields coupled to the photoactive layer with decreasing the thickness of the PEDOT: PSS layer. By optimizing the thickness of PEDOT: PSS buffer layer and the spectral overlap between Ag nanoprisms and active layer, the power conversion efficiency of polymer solar cells is enhanced to 3.82%, which is 1.26 higher times than that of the control device without Ag NPs layer.Secondly, we investigated the influence of different reaction time on the size, the density and the morphology of the Ag nanosheets. The Ag/Ag2 S nanosheets prepared via sulfuration under different reaction time are used to enhance the performance of hybrid solar cells. Hybrid solar cells with a structure of ITO/Ag/Ag2S: P3HT/Mo O3/Ag exhibit an open circuit voltage(Voc) of 0.33 V, short circuit current density(Jsc) of 20.54 m A/cm2, a fill factor(FF) of 50.21 %, and power conversion efficiency(PCE) of 3.50 %., which are 1.15 times than the Control device. We attribute the improvement of the efficiency to localized plasmon resonance(LSPR) induced by introducing the Ag nanosheets, which enhance the light harvest of active layer. The 3-D structure acts as the optical cavity for further improving the light absorption and increasng the exiton dissociation interface.Thirdly, we got Ag nanoparticles on the substrate by using the vacuum deposition so that we can study the influence between 3-D nanostructures and nanoparticles on the performance of the device. The device structure whose performance exhibits an open circuit voltage(Voc) of 0.28±0.01 V, short circuit current density(Jsc) of 11.44 m A/cm2, a fill factor(FF) of 40.01 %, and power conversion efficiency(PCE) of 1.21 % is ITO/Ag/Ag2S: P3HT/Mo O3/Ag. The PCE of hybrid solar cells by adding Ag nanoparticles are lower than devices with 3-D nanostructures. We attribute this to the less LSPR and the bad exciton dissociation caused by 2-D structures.