Synthesis And Photovoltaic Properties Of Novel Polymer Donor Materials Based On Benzotriazole

In recent years,as polymer solar cells?PSCs?could produce electric energy from the sunlight directly and possess the advantages of semitransparent thin film and flexibility in large area applications,the PSCs have attracted much more attention and been regarded as a key point to solve energy crisis.In particular,the power conversion efficiency?PCE?of PSCs based on wide bandgap polymers and non-fullerene acceptors has exceeded over 16%.In this dissertation,the briefly development of PSCs and some high-performance photovoltaic materials were systematically summarized and introduced.For the shortage of high-efficiency organic polymer donor materials and lack of design theory guidance for designing high-performance molecules,a series of alkoxy,alkylthio and strong electron-withdrawing sulfone unit inserted thiophene bridges were designed and synthesized in this thesis.This design strategy effectively reduces the HOMO levels,improve the ordered?-?stacking,and enhances the Voc,Jsc,and FF of the polymer donor materials,thereby obtaining high PCE.The molecular structures of these novel D units and polymeric monomers were fully characterized,and the photophysical properties,electrochemical properties,thermal stability and photovoltaic properties of polymer materials were investigated.Furtheremore,density functional?DFT?calculations were carried out to study geometric constructions and energy levels of the designed materials.The effects of polymer donors on their charge transport,carrier mobility and surface morphology were further studied.The relationships between molecular structure and photovoltaic performance were revealed.The main research contents of this thesis are as follows:1)The polymers PBTOR-FBTA,PBTOSR-FBTA and PBTSR-FBTA with a new type of bithiophene derivative substituted with alkylthio group as donor unit and benzotriazole as acceptor unit were designed and synthesized.The influence of the different numbers alkylthio group appending bithiophene unit on polymer performances were studied.It has been found that the alkylthio group substitution can effectively reduce the HOMO levels,improve the hole mobility,and promote the molecular?-?stacking,thereby obtaining higher open circuit voltage and short circuit current.In the fullerene-based solar cell?PC71BM?,a higher photovoltaic performance was observed for the PBTSR-FBTA-based device with a PCE of 6.25%,a J_sc of 12.66mA/cm²,a V_oc of 0.81 V and a FF of 60.94%,which is the highest reported for polymer containing bithiophene unit.Our research results obtained here indicates that properly incorporating alkylthio side chains in D-A type polymer is an efficient strategy to improve photovoltaic performance.2)Two novel polymers PTs-ffBT and PTs-FTAZ with novel A₁-A₂ configuration using the electron-withdrawing sulfone group as the novel acceptor A₁ unit,benzothiadiazole and benzotriazole as the acceptor A₂ unit,were designed and synthesized for application in photovoltaic materials.The influence of the different A and D groups on polymer performances were studied.Due to the intramolecular interactions between oxygen and sulfur atom?O-S?noncovalent bonds,which are benefical for enhancing planarity of the molecular backbone.As a result,It was found that this strategy is benefit for reducing the HOMO level,enhancing absorption scope and improving the hole mobility of the corressponding polymers.The impacts of different acceptor units on the optoelectronic properties,carrier mobility,the HOMO/LUMO energy levels,and the morphologies of blend films,as well as optimization on device performance were systematically investigated.The devices based on PTs-ffBT and PTs-FTAZ exhibit PCEs of 3.36%and 3.80%,respectively,which is the highest reported for polymer containing thiophene sulfone acceptor unit.This research results reported here clearly demonstrate that sulfone units can be well applied to polymer donor materials.3)The D-A type polymers PBS-FTAZS and PBCl-FTAZS with the BDT substituted with sulfur atom and chlorine atom as the donor unit and the thiophene bridged benzotriazole substituted with sulfur atom as the acceptor unit,were designed and synthesized.The influence of the different groups on polymer performances were studied.It was found that the introduction of sulfur atoms on the thiophene bridge can effectively reduce the HOMO level and enhance the ordered packing of the molecules.Meanwhile,the introduction of chlorine atoms on the BDT can further reduce the molecular level and increase the open circuit voltage.Based on ITIC as acceptor,the devices based on PBS-FTAZS and PBCl-FTAZS present a PCE of 4.65%and 6.28%,respectively.The results reveal that bridge sulfur atom can effectively improve the device performance of materials.