Design,Synthesis And Device Characterization Of Non-Fullerene Acceptor Materials Based On TTPBT System

Organic solar cells（OSCs）have attracted great attention of researchers due to their advantages such as lightweight,low cost,controllable color and solution processing.In recent years,due to the rapid development of non-fullerene acceptor materials,the efficiency of binary OSCs has exceeded 19%,and ternary OSCs have even exceeded 20%.Due to the decisive role of active layer materials in achieving photoelectric conversion,developing non-fullerene acceptor materials with complementary absorption and matching energy levels with donor materials is an effective method for achieving high-performance OSC devices.In addition,with the proposal of the strategy of"polymerized small molecule acceptors"（Polymerized small molecule acceptors,PSMAs）,ternary random copolymerization has also been proven to be an effective strategy for designing and synthesizing new molecular skeletons.Based on this,the main research work of this thesis is centered on the acceptor materials in the active layer,and the relationship between their properties and molecular structure is characterized by constructing devices.The main research content is as follows:1.Due to the strong absorption of naphthalene diimide（NDI）units in the short-wave direction,but their low light absorption coefficient(<4×10⁴ cm^-1),resulting in a low short-circuit current,which limits its application as an acceptor material in OSCs.However,Y-series acceptor materials have relatively weak absorption in the short-wave direction,with a strong absorption range mainly concentrated in the range of 780-1000nm,and have a high absorption coefficient(～1.39×10⁵ cm^-1),based on the complementary properties between the NDI unit and the Y-series unit described above,we designed and synthesized four polymer acceptor materials,PN1,PN5,PN10,and PN15（1,5,10,and 15 represent the molar percentage of NDI88 units in the system）,and matched them with the polymer donor material PBDB-T.The experiment shows that as the NDI unit is introduced into the system,the absorption in the short-wave direction increases,but at this time,the FF of the device also decreases,we systematically explored how to balance these two mutually exclusive factors,and ultimately achieved an energy conversion efficiency of 9.35%for devices based on PBDB-T:PN10.2.Since the introduction of alkyl chains into molecular systems has been proven to be an effective means to improve the solubility and electrochemical performance of materials,in the past,the substitution sites for the introduction of alkyl chains in Y-series acceptor material systems were mainly concentrated on the pyrrole ring of the central ring and the thiophene ring on the side.By using non-conjugated 1,6-bis（5-（trimethylsilyl）thiophene-2-yl）hexane as aπbridge,four non-fully conjugated polymer acceptor materials,PTH73,PTH55,PTH37,and PTH01,were designed and synthesized by controlling their ratio to 2,5-bis（trimethyl tin）thiopheneπbridges in the system.The possibility of photoelectric conversion and their photoelectric performance were investigated.The results showed that these four non-fully conjugated acceptor materials were able to undergo photoelectric conversion,and with the increase of the content of non-conjugated 1,6-bis（5-（trimethyltin）thiophen-2-yl）hexane in the system,the UV absorption spectrum of the materials slightly shifted blue,and their LUMO energy levels remained basically stable.The device was prepared by matching these four acceptor materials with the polymer donor material PBDB-T.Finally,the energy conversion efficiency of all-polymer solar cell devices based on these four acceptor materials was 10.52%,10.37%,10.26%,and 10.17%,respectively.3.Due to the direct impact of the symmetry of molecular structure on the stacking and photoelectric properties of molecules,and with the development trend of OSCs,we have found that the molecular junction symmetry of acceptor materials is gradually weakening,from the earliest fullerenes with excellent symmetric structures,to the later ITIC series acceptors with central symmetric structures,and then to the current Y series acceptors with chiral helical structures.Therefore,This article designed and synthesized an asymmetric non-fullerene acceptor material TTPBT-CPTIC4Cl by changing the type of end groups,and compared its photoelectric performance with TTPBT-IC8Cl and TTPBT-2CPT with symmetrical structures.The results showed that TTPBT-CPTIC4Cl with asymmetric end groups had a UV absorption spectrum between TTPBT-IC8Cl and TTPBT-2CPT,and its electronic band gap was the widest,this also provides a guarantee for achieving high open circuit voltage.