The Photophysical Properties Of Hybrid Plasmonic Nanostructures And Their Application In Non-fullerene Organic Solar Cells

In recent years,organic solar cells(OSCs)have received extensive attention due to their properties such as light weight,high flexibility,large-scale solution processing and low cost.So far,the power conversion efficiency(PCE)of OSCs based on nonfullerene acceptors has exceeded 18%,which presents broad prospects for future commercial application.Nevertheless,the contradiction between the short exciton diffusion length and the thick active layer of OSCs leads to insufficient light absorption,which could hinder the further improvement of device performance.As a result,it is necessary to develop a more efficient method for light harvesting to improve the light utilization efficiency of the devices.Meanwhile,with the global development of nanotechnology,nanomaterials have become one new kind of materials for photovoltaic application,providing new strategies for solving the aforementioned problem.Among them,metal nanostructures(MNS)have gained great attention due to their unique electrical and optical properties such as localized surface plasmon resonance(LSPR)which is an effective way to enhance the optical absorption of OSCs,while low-dimensional MNS such as metal nanowires have been applied in flexible devices and achieved good fruits.In this thesis,a series of studies have been carried out on hybrid plasmonic metal nanostructures for different photovoltaic application(flexible OSC,semitransparent OSC).The main research contents and results are summarized which follows.Firstly,a plasmonic hybrid flexible transparent electrode(FTE)based on Ag nanowires(AgNWs),Ag nanoparticles(AgNPs)and graphene was prepared by an allsolution-processed to replace traditional ITO electrode.The results show that the resonance coupling between the excitons in the active layer and the surface plasmon increases the light-trapping ability of the active layer due to the plasmonic coupling effect of AgNPs and AgNWs,while the introduction of exfoliate graphene improves the conductivity and flexibility of the FTE.This hybrid FTE with high optical transmittance and electrical conductivity,has a specific absorption in the ultraviolet region(<380 nm),which can be considered as a built-in ultraviolet filter to prevent the photodegradation effect of ultraviolet light on organic photovoltaic materials.Finally,the non-fullerene flexible OSC with the PBDB-T: ITIC system achieved a PCE of8.15%,and excellent mechanical flexibility and UV durability.Secondly,an enhancement in broadband absorption from visible to near-infrared wavelengths was realized by applying hybrid MNS based on gold nanobipyramids(AuNBPs)and gold nanospheres Au NSs)in non-fullerene OSCs.Combining optical simulation and experimental characterization,the effects of introducing hybrid MNS into the hole transport layer Poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate)(PEDOT:PSS)on the optical properties and surface morphology of the films were systematically investigated.The photovoltaic performance and photophysical properties of the device were also studied.By optimizing the fabrication process,the PCE of the non-fullerene OSC with PM6:Y6 system reaches 16.38%,while the external quantum efficiency(EQE)of the device is significantly improved in a broadband range from the visible to the near-infrared region.Finally,the thesis investigates semitransparent organic solar cells(ST-OSCs)based on AuNBPs to achieve an enhancement in near-infrared light absorption.An ideal ST-OSC should maintain a proper balance between absorption and transmission in the visible range,while having a high light utilization efficiency of non-visible photons,especially in the near-infrared region.In this thesis,the effects of the thickness of ultrathin metal top electrodes and different donor: acceptor ratios of active layer on the photovoltaic performance and average visible transmittance(AVT)of ST-OSC were systemtically investigated.The PCE of the optimal device reaches 10.43%,along with an AVT of 24.5% and a light utilization efficiency(LUE)of 2.56.On this basis,AuNBPs with near-infrared LSPR were introduced into PEDOT: PSS to achieve enhanced light absorption of the active layer in the near-infrared region.The results show that the PCE of the device increases to 11.55% after adding AuNBPs without affecting the AVT of the device,while the maximum LUE reaches 2.80.Improving the near-infrared light absorption of active layer through the LSPR effect of AuNBPs provides a feasible approach to the development of high-performance ST-OSC.