| Porphyrin molecules play important roles in biology such as in photosynthesis and oxygen transport.The porphyrin derivative chlorophyll a in plants absorbs photons from sunlight and converts these into chemical energy through a charge-transfer process.As a new kind of functional organic materials,porphyrin derivatives are getting a large amount of attention due to their excellent optical and electrical properties.In addition,the absorption of porphyrins lies in both the blue（Soret band）and red（Q bands）parts of the visible spectrum,and can easily extend into the near-infrared（NIR）region when donor-acceptor structures are incorporated.These properties enable porphyrins to be successfully applied in photovoltaic devices,such as dye-sensitized solar cells with power conversion efficiencies（PCEs）over13%.Porphyrin-based semiconductors have also been widely reported as electron donors in bulk-heterojunction（BHJ）organic solar cells（OSCs）.In particular,a series of molecules with porphyrin as the core and electron-deficient units as end groups have been developed to create materials with a broad absorption in the visible and NIR absorption regions.The incorporation of these materials as electron donors has resulted in increased PCEs of 8%in singlejunction solar cells and 11%in ternary and tandem solar cells.In principle,porphyrin is an electron-donating unit and,hence,it seems a difficult task to design electron acceptors based on porphyrins as a component in non-fullerene organic solar cells（NFOSCs）.In our previous study a star-shaped electron acceptor based on porphyrin as a core and perylene bisimide as end groups was constructed for application in non-fullerene organic solar cells.The new conjugated molecule exhibits aligned energy levels,good electron mobility,and complementary absorption with a donor polymer.These advantages facilitate a high power conversion efficiency of 7.4%in non-fullerene solar cells,which represents the highest photovoltaic performance based on porphyrin derivatives as the acceptor.In this dissertation,porphyrin electron acceptor is the research object.A series of polymers and small molecule materials were synthesized and their photovoltaic properties were studied systematically,which provided a new idea for the design of acceptor materials for organic solar cells.The main research results are as follows:1.We explore a new near-infrared electron acceptor naphthalenediimide-porphyrin（NDI-Por）by using electron-donating porphyrin as the core,and four NDI as end groups with ethynyl as linkers attached to the meso-position of porphyrin.This star-shaped molecule exhibits absorption spectra up to 900 nm.NDI-Por was incorporated into non-fullerene solar cells as an electron acceptor,and together with a wide-band gap polymer donor,an initial power conversion efficiency of 1.8%could be achieved.In particular,the solar cells exhibit a broad photo-response from 300 nm to 900 nm.2.For the first time,small bandgap porphyrin-based polymer acceptors with low-lying frontier energy levels and good crystallinity were developed for application in non-fullerene organic solar cells,in which a broad photoresponse from 300 nm to 1000 nm and an initial PCE of 3.46%have been achieved.3.Porphyrin-based molecules have been widely used in dye-sensitized solar cells and bulk heterojunction solar cells,but their application in field-effect transistors（FETs）is limited.In this work,two conjugated polymers based on diketopyrrolopyrrole and porphyrin units were developed for FETs.The polymers exhibit extra-low band gap with energy levels close to-4.0 eV and-5.0 eV due to the strong electron-donating and withdrawing ability of porphyrin and diketopyrrolopyrrole.With additionally high crystalline properties,ambipolar charge carrier transports with a hole mobility of 0.1 cm2V-1 s-1 in FETs were realized in these polymers,representing the highest performance in solution-processed FETs based on porphyrin unit. |
