Synthesis Of A Novel Multifused Tetracyclic Arenes Based On Benzothiadiazole And Its Photovoltaic Applications

Polymer solar cells (PSCs) have many merits such as low weight, low cost, easy fabrication, flexible and tunable properties and have attracted much attention. After continuous research in the past few years of national researchers, The efficiency of organic solar cells has reached a level of8.5%, but there is still a long way to go for the commercial applications.The efficiency and lifetime are two key factors for polymer photovoltaic solar cells and have a great relationship with the conjugated material selected.How to design and synthesize π-conjugated polymers with suitable band gap, absorption spectrum and carrier mobility, is currently a research priority of the polymer photovoltaic solar cells.Compared with other conjugated polymers, poly(benzothiadiazole) derivatives exhibit some unique merits such as excellent thermal stability and Chemical stability, strong electron-withdrawing ability and higher oxidation potential duo to their rigid plane. Making the poly(benzothiadiazole) and derivatives become a widespread concern polymer donor material forced planarization by covalently locking neighboring aromatic units is an effective approach to reduce the band gap, because the parallel p-orbital interactions can facilitate π-electron delocalization and elongate effective conjugation length.Furthermore, rigid structures can reduce the rotational disorder around interannular single bonds to lower the reorganization energy, which is beneficial to improve charge mobility.In this dissertation, a novel multi-fused building block benzothiadiazoledithio-phene was prepared by covalently locking thiophene units at both sides of benzothiadiazole (BT) for the first time. On the basis of this new building block, a series of conjugated copolymers containing either electron-rich comonomers such as carbazole (P1), benzodithiophene (P2and P3), thiophene (P4) or electron-deficient comonomers such as thiazolothiazole (P6) and homopolymer (P5) were designed and synthesized. All of the polymers had good solubility in common organic solvents. The thermal stability, optical and electrochemical properties, and photovoltaic performance of the polymers were systematically investigated. The thiophene units, which were covalently fastened to the BT moiety, enlarged the planarization of the polymer back bone and thus induced stronger intermolecular π-π interaction, meanwhile, decreased the electron-withdrawing ability of the BT unit. Under AM1.5G illumination (100mW/cm2), the device based on the P3:PC7oBM (1:1, w/w) as the active layer exhibited an open-circuit voltage of096V, a short-circuit current of5.39mA/cm2and a fill factor of0.42, leading to decent power conversion efficiency of2.15%.