Study On Performance Improvement Of Polymer Solar Cells Doped With Alkali Metal Salts

With the gradual depletion of non-renewable fossil energy and people’s growing awareness of loving life and protecting the environment,many countries all over the world have put the development of green renewable resources on the work agenda,solar energy as a pollution-free and can be seen as an almost inexhaustible resource is more and more popular.Solar Cell Photovoltaic Technology is an effective way to convert solar energy into electrical energy.The scientific research work on solar cells has never stopped,the preparation technology is gradually mature.Polymer solar cells have many unique advantages,such as low cost,good flexibility,simple process and easy large-area preparation,etc...However,compared with the traditional silicon solar cell,the efficiency of polymer solar cell is still at a low level,and the stability needs to be improved,which is a key factor to restrict the commercialization of polymer solar cells.With an eye to improving the energy efficiency of polymer solar cells,researchers are constantly upgrading the materials,structures and fabrication techniques of the devices.At present,the direction of improving the performance of polymer solar cells can be divided into two aspects:one is to project and synthesize new photoactive layer materials,the other is to interface engineering.ZnO is a kind of wide band gap semiconductor materials with good electronic transmission performance,suitable energy band position,controllable morphology,simple preparation process and low cost,it is widely used as the electron transport layer material for polymer solar cells.However,there are a lot of bulk defects in ZnO thin films,which have a great influence on carrier transport and interface contact in polymer solar cell devices.In addition to directly modifying the cathode to achieve an effective ohmic contact at the interface,the use of alkali or alkali salts as n-type dopants to modify the electron transport layer is an important way to lower the electron injection barrier.In this paper,the effects of different alkali metal salts doped ZnO films on the function of the electron transport layer and the performance of the devices are investigated.ITO/ZnO or alkali metal salts doped ZnO/PTB7:PC₇₁BM/Mo O₃/Ag polymer solar cells were prepared by using Li Ac and Cs Ac as dopant,the mechanism of electronic transport layer of ZnO doped with alkali metal salts to improve the performance of the devices was investigated by various characterization methods,and the influence of different doping concentrations on the experimental results was investigated.The experimental results show that the alkali metal salt doped ZnO electron transport layer does provide a favorable effect on the electronic properties of polymer solar cell devices,the short circuit current density of the device increased from 15.632 mA/cm² to 18.377 mA/cm²,and the relative power conversion efficiency increased from 7.581%to 9.074%.The introduction of alkali metal salts reduces the electron implantation barrier and the contact resistance of the interface,thus facilitating the process of charge transport and transfer,the electron mobility of the optimal doping concentration device increased from 4.0867×10^-4cm²V^-1s^-1 to 1.1877×10^-3cm²V^-1s^-1.At the same time,the defect states on the inner and surface of ZnO films modified by alkali metal salts are reduced,which reduces the resultant charge recombination loss and optimizes the interface contact between the electron transport layer and the active layer,it provides a more convenient condition for carrier transmission.In addition,the active layer also has the certain degree enhancement to the light absorption ability,more exciton production,enhances to the photocurrent.In this paper,the study of alkali metal salt doping to improve the performance of polymer solar cells provides a reference for the buffer layer optimization in the field of polymer solar cells.