Investigation On Charge Transport Process In Organic Bulk Heterojunction Based On Acceptor Structural Change

Under the background of global carbon neutrality and energy transformation,the demands for green,clean,renewable,and low-cost energy have stimulated the momentum of organic photovoltaic research.In recent years,organic solar cells have developed rapidly.Bulk heterojunction organic solar cells have developed as promising cost-effective alternatives to conventional inorganic solar cells.Bulk heterojunction is formed by mixing electron donor materials and electron acceptor materials.Due to the development of non-fullerene acceptor materials,the power conversion efficiency of organic solar cells has exceeded 19%.The charge transport properties have an important impact on the photocurrent of photovoltaic devices,which in turn affects the power conversion efficiency of photovoltaic devices.Therefore,it is important to investigate the charge transport behavior in bulk heterojunctions.In this work,the charge transport properties of bulk heterojunction based on several common non-fullerene acceptor materials are investigated experimentally.The intrinsic mechanism of charge transport is explored through molecular dynamics simulation and quantum chemical calculations.The detailed research work is as follows:(1)PM6:IT-4F and PM6:Y6 bulk heterojunction systems are selected to compare their electron transport properties by using molecular dynamics simulations and quantum chemical calculations.The mobility of multiple acceptor clusters is calculated.Finally,the calculated mobility is compared with that obtained by the space charge limited current method.The mobility calculated by quantum chemistry is not completely consistent with the mobility measured experimentally,but both of them can qualitatively measure the charge transport properties of bulk heterojunction.(2)In organic photovoltaic devices,fluorination strategy is one of the most effective and popular molecular modification methods for developing new materials for organic photovoltaic cells.In this work,two kinds of non-fullerene bulk heterojunctions based on Y5 and Y6 are selected as the object of the investigation.The performance of PM6:Y6 photovoltaic devices is significantly better than PM6:Y5 photovoltaic devices.The electron mobilities of PM6:Y5 and PM6:Y6 bulk heterojunction films measured experimentally are 5.76×10-7 cm2V-1s-1 and 5.02×10-5 cm2V-1s-1,respectively.Using molecular dynamics simulations and quantum chemical calculations,the difference of electron mobilities of PM6:Y5 and PM6:Y6 BHJ films is explored from a microscopic perspective.Halogen bonds can be formed between halogen atoms in Y6 dimers,which can provide external channels for the transport of electrons in the acceptor molecules.The electron mobility and electron transport performance of the PM6:Y6 bulk heterojunction have been improved.