Enhancement Of Power Conversion Efficiency In Organic Photovoltaic Devices By Employing Micro-nano Composite Structures

Organic photovoltaic(OPV)has the immense potential to be the next generation energy harvesting devices due to their light weight,low cost,flexibility and environmental friendliness.However,the thickness of the active layer in single-junction OPVs is generally thin,which leads to the low optical absorption efficiency of single-junction OPV.By introducing different microstructures into OPVs,the power conversion efficiency(PCE)of OPVs can be effectively improved.For example,by introducing the micro-period grating structure into OPVs,the PCE of OPVs can be increased effectively due to the light scattering.By introducing nano-scale periodic metal grating structure or metal nanoparticles into the OPVs,the light absorption efficiency of OPVs can be increased effectively due to the plasmon field enhancement effect induced by the excited surface plasmon at the interface between metal and dielectric.In order to further enhance the PCE of the OPVs,in this work,micro-nano composite structures were introduced into the OPVs.The PCE of the OPVs was increased effectively due to absorption enhcanement,which was induced by the scattering effect of micro-grating and plasmon field enhancement effect at the interface between nano-grating metal electrode and active layer.On the other hand,by employing low work function alloy nanoparticle as the intermediate layer in the tandem OPVs,the efficiency was improved obviously due to the decrease of electron injection barrier.The main contents involved in this dissertation are listed as follows:1.Preparation of periodic micro-nano structures with different morphologies based on photolithography technology and laser dual-beam interference technologyBased on the traditional photolithography technology,the one-dimensional rectangle grating and two-dimensional rectangle grating with different period were fabricated on the SU-8 negative photoresist by using different patterned masks;the one-demensional nano-grating structures were fabricated by using double-laser beam interference technology;Mainwhile,combine the phtotolithography technology and double-laser beam interference technology,the micro-nano composite structures were fabricated through one time photoresist coating and two times continuous exposures.2.Improve the PCE of OPVs by employing micro-nano composite gratingBy using the metal-organic multi-source vacuum vapor deposition system,the OPVs with the micro-nano composite grating were fabricated.The results of experiment show that the light absorbing efficiency of OPVs with micro-period rectangle grating was effectively improved,which was mainly attributed to the scattering effect of the grating.Compare with the plane OPVs,the PCE of grating OPVs exhibit 7.08% increment.Mainwhile,the light absorption efficiency of the OPVs with nano-period grating structure was enhanced obviously due to the surface plasmon field-enhancement effect at the interface between the grating metal electrode and the active layer.Compare with the plane OPVs,the PCE of the OPVs with nano-grating exhibit 9.7% increment.Finally,the light absorption efficiency of the OPVs with micro-nano composite grating was further improved due to combination of the scattering effect and the surface plasmon field-enhancement effect.Compare with the plane OPV,the PCE of the OPV with the micro-nano composite grating exhibits 13.6% increment.3.Improve the PCE of tandem OPVs by employing low work function alloy nanoparticle intermediate layerReplacing the Ag intermediate layer,low work function Ca-Ag,Mg-Ag,and Al-Ag alloy nanoparticle were introduced into the tandem OPVs as the intermediate layer.The results show that the barrier between the cathode buffer layer and the convertional Ag nanoparticle intermediate layer can be effectively reduced by using low work function alloy nanoparticle intermediate layer.Hence,the series resistance of tandem OPV was reduced obviously.Compare with the PCE of the tandem OPV with Ag nanoparticle intermediater layer,the PCE of the tandem OPV with Mg-Ag alloy nanoparticle intertermediate layer exhibits 7.5% increment.