The Study Of Polymer Solar Cells With Multiple Optical Spacers

Polymer Solar Cell?PSC?is one of the most important research subjects because of its many advantages such as light weight,simple manufacturing process,low cost and it's compatibility with flexible substrates.In recent years,the inverted polymer solar cell?IPSC?with transparent electrode as the bottom electrode and the metals with high stability such as gold or silver as the top anode has been deeply studied and widely used.The absorption of the incident light in the active layer of IPSC is a key parameter to determine the performance of the IPSC.Using a Titanium oxide or Zinc Oxide film as optical spacer layer between the cathode and the active layer has been proved to be an effective strategy to enhance the light absorption of the active layer.Moreover,the ZnO or TiO_x films grown on the cathode also act as the cathode buffer layer,which can create an energy cascade from the LUMO of the cathode and the active layer,facilitating the extraction of the electrons and blocking the hole transmission.However,the optical spacer reported in literatures was all made of monolayer with a thickness between 30-100nm.By further increasing the thickness of the spacer layer,the modulation range of the optical intensity distribution in the device could increase but the series resistance of the device could also increase due to the poor crystalline quality of ZnO or TiO_x thin films prepared with sol-gel method at low temperature.As a result,the short circuit current decreased and the performance of the IPSC degraded.Thus,it‘s of great importance to find a technology that can enhance the light absorption of the active layer without increasing the series resistance of the whole device.In this thesis,polymer solar cells with multiple optical spacers was proposed and fabricated.The proposed structure can effectively enhance the absorption of the active layer and further improve the power conversion efficiency?PCE?of the device.First,we use the transfer matrix method to calculate the distribution of incident light and the short circuit current in a IPSC with multiple optical spacers consisting of undoped ZnO film and Cs doped zinc oxide?CZO?films with different doping concentration of 0.0025M,0.005M and 0.01M.The simulation results show that the multiple optical spacers provide a cascade of refractive index between the ITO substrate and the active layer when the CZO film with a decreasing doping concentration was deposited on ITO successively,resulting in an increase of e light absorption in active layer and short-circuit current density(J_SC)significantly.Then,IPSCs with multiple optical spacer were prepared.IPSC with two?0.0025M CZO/ZnO,the 0.0025M is the cesium concentration?,three?0.005M CZO/0.0025M CZO/ZnO?and four optical spacers?0.01M CZO/0.005M CZO/0.0025M CZO/ZnO?and undoped ZnO film?reference device?were fabricated successively.The results show that the performance of PSC with three optical spacers was maximum and the PCE was improved 27.9%compared with the IPSC with monolayer optical spacer and reached 3.9%.The results show that IPSCs with multiple optical spacers can improve the light absorption of the active layer and the PCE of the devices.The proposed structure provides an effective method to improve the performance of polymer solar cells.