Synthesis And Properties Of Thienopyrroledione-based Functional Organic Solar Cell Materials

Bulk-heterojunction (BHJ) solar cells based on polymer or small molecule donorand fullerene acceptor networks have made a breakthrough success for efficient solarenergy application. Low band-gap D-A conjugated molecules incorporatingelectron-donating (D) and electron-accepting (A) units on the backbone have becomethe most important donors in BHJ solar cells. To optimize power conversionefficiency (PCE), attention has been paid to design narrow-bandgap polymers or smallmolecules to maximize short-circuit current (Jsc), and to lower the highest occupiedmolecular orbital (HOMO) to increase open circuit voltage (Voc). Dye-sensitized solarcells (DSSCs) continue to be actively pursued as low cost alternatives with highextinction coefficients in traditional photovoltaics. Dyes with D-π-A structure(commonly carboxylic acids, rhodanine as A units) have been known to be effectivefor intramolecular charge transfer, which is convenient for highly efficient DSSCapplications. Main points are as follows:1. P1and P2containing thienopyrroledione (TPD) were designed and created viaSonogashira and Stille polymerization, respectively. Besides, the optical-electronicproperties with thermal behavior and photovoltaic properties have been discussed.Results show that the introduction of Pt in P1possesses better quality, such as thermalstability and film quality, with the highest Vocand Jsc so the solar device shows anmuch higher efficiency of0.65%than that of P2(0.0088%).2. Small molecules S1-S4with A-D-A structure contain carbazole as the donorand benzothiadiazole as the acceptor, via controlling the presence of alkyl substituentson the thienyl units on the block and different end groups for comparison. Resultsshow that the optical and chemical bandgaps of these molecules belong to narrowbandgaps, and S3holds the best PCE of0.35%with the highest Vocof0.76V, due tothe fact that alkyl substituents could improve solubility and film quality and strongerwithdrawing unit malononitrile could extend the absorption range compared with3-ethylrhodanine, which benefits the application on BHJs.3. The D-π-A structural dyes D1and D2have the same backbone withthienopyrroledione as π-bridge but different anchor groups, which are cyanoacrylicacid and2-(1,1-dicyanomethylene)rhodanine, respectively. We carried out asystematic study of the effect of two dyes with different anchor groups. Resultsexhibits that2-(1,1-dicyanomethylene)rhodanine effectively extends the absorption range with larger molar absorption coefficient and appropriate HOMO energy level.And the optical bandgaps are1.93eV、1.86eV, respectively; electric bandgaps are1.61eV、1.58eV, respectively.