Study On Polymer Solar Cells With Zno-based Core-shell Nanorods As Electron Transport Layer

Organic solar cells,especially polymer solar cells（PSC）with bulk heterojunction structure have attracted considerable attentions due to their potential for the low cost,light weight and forming a uniform film on the flexible substrates.In order to improve the stability of device,the inverted polymer solar cell（IPSC）has been extensively investigated and widely applied in the field of organic photovoltaics.Direct band-gap semiconductor ZnO has been widely used as electron transporting layer（ETL）for IPSCs because of its high transmittance in visible range,high conductivity and possibility for large scale production.In recent years,a variety of inorganic semiconductor nanostructures such as nanoparticles,nanoridges and nanorod arrays have been introduced as acceptor,ETL or transparent electrode.Zn O nanorod array（ZnO-NRA）synthesized at a low temperature by hydrothermal growth method has a high electron mobility,effective hole blocking ability,strong environmental stability and compatibility with a variety of substrate materials,which is often used in polymer solar cell as ETL.Not only can the NRA accommodate thicker light-absorbing materials with its large specific surface area,but also provide an efficient transmission path for the electrons.However,the performance of IPSC with Zn O-NRA as the ETL is far from satisfactory due to the poor crystallization inside of the ZnO-NRA,high defect density on the surface of ZnO-NRA,which results in inefficient charge transfer and unsatisfactory charge recombination at the interface between the active layer and the NRA,decrease the power conversion efficiency of the IPSC.To solve the above problems,in this paper,an inverted structure polymer solar cell with core-shelled cesium doped zinc oxide nanorod array（CZO-NRA）as ETL was designed and prepared.Compared with ZnO-NRA,CZO-NRA as a shell material has better crystalline quality and conductivity,and provides a good transmission channel for electrons.In addition,study has shown that a proper amount of cerium doping can reduce the work function of Zn O-NRA.The LUMO energy levels of ITO,ZnO-NRA,CZO-NRA and active layers form a stepped barrier,which is more conducive to the extraction of electrons.The paper first explored the basic growth process of ZnO-NRA as an electron transport layer,including the optimal concentration of ZnO-NRA and the metal doping process.Zinc oxide seed layer was prepared by sol-gel method,ZnO-NRA was prepared by a chemical bath method as an electron transport layer.An IPSC device with a structure of ITO/CZO-NRA/P3HT:PC₆₁BM/MoO₃/Ag was prepared.When the concentration of growth solution reached 0.025 M/L with Cs doping concentration reaching 0.75 mM,the device efficiency reached a maximum value of1.79%which was 43.2%higher than that of the undoped device.Next,in order to further improve the performance of the device,core-shelled CZO-NRA was grown by two-growth method as the ETL,The device structure was ITO/ZnO-NRA/CZO-NRA/P3HT:PC₆₁BM/MoO₃/Ag.The Kelvin probe test results showed that the work function of 0.75 mM CZO-NRA was 0.3 eV lower than that of undoped ZnO-NRA,and the energy conversion efficiency of the prepared device reached 2.57%,which was 43.6%higher than that of 0.75 mM CZO-NRA with single growth.In this paper,the core-shelled ZnO-NRA/CZO-NRA was used as the ETL of the inverted polymer solar cell,which improved the interface contacting quality between the electron transport layer and the active layer,reduced the interaction barriers between the cathode and the active layer and improved the performance of the device.The structure provides a new idea for the application of nanostructures in the field of polymer solar cells and has a good application prospect.