Nano/micro-structure Modification For Organic Solar Cells

Nano/Micro-Structure Modification for Organic Solar CellsOrganic solar cells?OSCs?have the advantages of light-weight,ease-fabrication,low cost,low pollution,large area preparation,and flexibility.OSCs have irreplaceable market value especially in curtain walls and vehicle-mounted energy sources.The low power conversion efficiency?PCE?is the bottleneck of the commercialization of OSCs.This is mainly due to the inefficient charge and light collection.Commonly,a thin active layer was used to promoting the charge extraction,which limits the absorption of the active layer.In order to improve the device performance with a thin active layer,this thesis carried out light manipulation strategies to enhance incident light absorption and surface modification strategies to promote the charge collection.The thesis content includes:First of all,quasi-period moth-eye structures were prepared and transferred onto electron transporting layer ZnO and glass substrate using soft nanoimprint lithography.Compared to the reference device,a 9.2%increase in PCE was obtained for the OSCs with moth-eye patterned ZnO electron transport layer.The device performance was further improved with the introduction of moth-eye anti-reflection film.Especially,over 10%PCE was obtained for the device based on PTB7-Th:PC₇₁BM active layer.By analyzing the absorption spectrum and theoretical simulations,the mechanisms of the light manipulation in OSCs were summarized as the antireflection effect of the antireflection layer,the waveguide resonance effect,self-enhanced absorption,surface plasmon resonance and backscattering effect.Secondly,monodisperse Zn O colloidal spheres and polydisperse Zn O colloidal spheres were synthesized using a two-step method.The mixture solution of ZnO colloidal spheres and ZnO nanocrystalline were spin-coated onto ITO and glass,forming electron transporting layer and anti-reflection film.The PCE of the OSCs based on PTB7-Th:PC₇₁BM was improved by 16%.By analyzing the transmission spectrum and theoretical analysis,the light manipulation mechanisms of the ZnO colloidal spheres in OSCs were concluded as:1.the polydisperse ZnO colloidal spheres scatter the incident light.2.Surface plasmon resonance and backscattering phenomenon were initiated by the metal electrode.Then,the mix films of ZnO and Al₂O₃ were prepared by sol-gel method and used as electron transport layer.Through the characterization of the optical and electrical properties of the device,it was found that an interface dipole layer on the surface of ZnO was introduced;the defects on ZnO surface were passivated;the refractive index of electron transporting layer was slightly increased.Therefore,monomolecular recombination and bimolecular recombination were inhibited in ZnO:Al₂O₃-based OSCs,and the electromagnetic field was concentrated in the active layer.An EQE over 90%and a certified PCE over 13%were obtained by further introduction of moth-eye structure and non-fullerene acceptor.