Application Of Organic Small Molecule Doped ZnO In High Efficiency Organic Solar Cells

In the 21 st century,the world economy and technology have begun to develop rapidly at unprecedented speed.With the rapid development of population,the population growth is also gradually showing a blowout trend,which also causes the increasing demand for energy in the world today.Since the beginning of last century,traditional fossil energy has been widely used worldwide.So the exploitation and application technology of fossil energy has already met quite mature conditions,which has caused many countries to ignore the pollution of fossil energy.Compared with other research fields,solar cells rely on their own excellent performance,such as the inexhaustible advantages of solar energy,low cost and no pollution to the environment,and have become a new and promising research direction in the research field.Traditional photovoltaic industry,with silicon based solar cells as the main application carrier,has considerable solar energy conversion efficiency,but its production environment requirements are relatively strict,raw material costs cannot be high,and there is inevitable pollution problem in the production process.Therefore,researchers began to focus on the production and processing of solution Solar cell.Because of its low production cost,it can be made into lightweight flexible devices,and can also be processed in large areas.Therefore,organic solar cells have a very good research prospect and high commercial value.High efficiency organic solar cells usually use bulk heterojunction active layer blended with donor and acceptor as light absorbing layer,and combine with electron transport(hole blocking)and hole transport(electron blocking)on both sides to collect photogenerated electron holes respectively,and finally form photocurrent in external circuit.In order to improve the energy conversion efficiency of organic solar cells,on the one hand,researchers actively develop new donor acceptor material blends to improve the absorption and utilization of light,and optimize the carrier generation efficiency and improve the device performance by adjusting the morphology of the active layer.Another important direction of organic solar cell optimization is to develop new and efficient transport layer materials,so as to effectively extract and collect the free carriers generated in the photoactive layer.In order to develop organic solar cells with higher performance,researchers usually use ZnO as the front electron transport layer and Mo O3 as the back hole transport layer.This device can effectively match the vertical phase separation in the photoactive layer,which is conducive to the separation and collection of electron holes.In this structure,the performance of ZnO electron transport layer largely determines the charge extraction and carrier recombination at the interface,so it has a significant impact on the device performance.As a result of these defects,such as the interface defects of ZnO,the carrier trapping is increased..This situation is particularly serious in ZnO processed at low temperature,because the ZnO reaction is not sufficient at low temperature,and it is easier to produce a large number of oxygen vacancy electron traps.At present,lowtemperature ZnO used for flexible device preparation is a promising research topic in organic solar cells,so how to improve the photoelectric performance of lowtemperature ZnO transport layer and develop high-performance ZnO electron transport layer preparation strategy become a key problem.Based on the above problems,this paper adopts an optimization strategy of organic small molecule doping.By introducing two kinds of organic small molecules designed by our laboratory into the ZnO film matrix,two kinds of organic-inorganic hybrid composite ZnO electron transport layers are constructed.Photogenerated carriers can be produced by irradiating small organic molecules.Due to the matching of energy levels,photogenerated carriers can be injected into the ZnO layer through the charge transfer process to provide additional carriers.These additional carriers can fill the electron deficient trap states,improve the electron concentration of ZnO,improve the carrier mobility,and suppress the defect states at low temperature Auxiliary composite problem.Therefore,this paper will be divided into the following two parts.Part one: in view of the energy level position of a large number of defects on ZnO surface,an optimization strategy is proposed.A matching 2-pyran-4-ylidenemalonitrile-di(3-hexylthiophene)(tpt-s)is designed and doped into ZnO to prepare ZnO: tpt-s composite electron transport layer.Finally,we prepared an efficient ZnO electron transport layer by sol-gel method at low temperature(130 C).The experimental results show that the electronic quality of ZnO interlayer can be improved by the introduction of tpt-s.On the one hand,the doped tpt-s molecules can passivate the uncoordinated defects of ZnO surface by forming N-Zn bond in the active layer.On the other hand,the light induced charge transfer of tpt-s,which is produced by the light source,is further filled with the trap state of the electron lacking in ZnO,which improves the electron mobility of ZnO and reduces the occurrence of charge recombination.By using square pulse irradiation devices with different intensity,we also reveal that the negative process of charge capture / capture observed in the controller is significantly inhibited after doping with tpt-s.Finally,we made pbdb-t-2f:it-4f and ZnO:TPT-S The PCE values(energy conversion efficiency)of the non fullerene organic solar cells(OSCs)as the cathode intermediate layer have reached12.62% and 11.33% on the rigid and flexible substrates.The results show that the hybrid ZnO is practical in high performance flexible devices.Part two: on the basis of the first success,we design another new organic small molecule ttzbr based on the summarized molecular design strategy,namely,the nitrogen containing,energy level matching with ZnO.We doped ttzbr into ZnO precursor and finally made ZnO ttzbr composite film.The experimental results show that ttzbr also has the function of passivating ZnO structure defects and filling the electron traps in ZnO by charge transfer under light.The feasibility and universality of our design strategy are demonstrated.After a series of tests and analyses,the organic small molecule can also transfer the photoinduced electrons to ZnO and fill the defect state after being illuminated.The design strategy enables ZnO to increase the electron concentration,inhibit the occurrence of carrier recombination,increase the electron mobility,and improve the efficiency of charge extraction,reduce the recombination of carriers at the interface,and prolong the life of the light induced carriers.Finally,the ZnO:TTzBr At 100:1 mass ratio,finally,we made PTB7:PC71BM as active layer,with ZnO:TTzBr As the cathode intermediate layer,the optimal energy conversion efficiency(PCE)of the fullerenyl organic solar cell OSCs is 10.59%.