2-Alkyl-5-thienyl-Substituted Benzo[1,2-b:4,5-b′]dithiophene-Based Donor Molecules for Solution-Processed Organic Solar Cells

Abstract

In this study, we have strategically designed and convergently synthesized two novel, symmetrical, and linear A-D-A-type π-conjugated donor molecules (TBDTCNR, TBDTCN), each containing a planar electron-rich 2-octylthiene-5-yl-substituted benzodithiophene (TBDT) unit as the core, flanked by octylthiophene units and end-capped with electron-deficient cyanoacetate (CNR) or dicyanovinyl (CN) units. We thoroughly characterized both of these materials and investigated the effects of the end groups (CNR, CN) on their optical, electrochemical, morphological, and photovoltaic properties. We then fabricated solution-processed bulk heterojunction organic solar cells incorporating TBDTCNR and TBDTCN. Among our tested devices, the one containing TBDTCNR and [6,6]-phenyl-C61-butyric acid methyl ester in a 1:0.40 ratio (w/w) exhibited the highest power conversion efficiency (5.42%) with a short-circuit current density (Jsc) of 9.08 mA cm(-2), an open circuit voltage (Voc) of 0.90 V, and an impressive fill factor (FF) of 0.66 under AM 1.5G irradiation (100 mW cm(-2)). The FFs of these solution-processed small-molecule organic solar cells (SMOSCs) are outstanding when compared with those recently reported for benzodithiophene (BDT)-based SMOSCs, because of the high crystallinity and excellent stacking properties of the TBDT-based compounds.

Synergistic Effects of Morphological Control and Complementary Absorption in Efficient All-Small-Molecule Ternary-Blend Solar Cells

“…For the device prepared from the SMD:PCBM binary blend system, we obtained a value of V oc of 0.73 V (Table 1), consistent with literature reports. 37,38 Device performance of the binary BDT6T:PCBM blend system is shown in Figure S2 and Table S2, which is consistent with a previous study where V oc has value of 0.90 V. 34 25,40 Therefore, the charge transfer state energy and, consequently, the value of V oc of the ternary blend changes as the ratio of either the donors or acceptors is changed. This phenomenon allows higher values of V oc in ternary D/D/A systems than are possible in binary D/A systems.…”

Quantitative Characterization and Mechanism of Formation of Multilength-scale Bulk Heterojunction Structures in Highly Efficient Solution-Processed Small-Molecule Organic Solar Cells

“…The synthesis of TBDTCNR as the donor has been described in detail previously. 32 Similar to the conditions for preparing the active layers of the solution-processed SM BHJ blend films, the samples for synchrotron scattering experiments were prepared through spin-casting of blend solutions of TBDTCNR and The active layers, prepared at TBDTCNR:PC 61 BM weight ratios of 1:0.4, 1:0.75, and 1:0.9, were annealed at room temperature for 30 min under a nitrogen environment in the glovebox. For the film prepared at a 1:0.4 weight blend ratio, thermal annealing was performed at 75, 100, or 125°C for 30 min to preanneal the active layer.…”

Effect of the π-conjugation length on the properties and photovoltaic performance of A–π–D–π–A type oligothiophenes with a 4,8-bis(thienyl)benzo[1,2-b:4,5-b′]dithiophene core

“…Structure modifications of the BDT core with aromatic units extend the π-conjugation of BDT unit to a two-dimensional structure, which increases intermolecular interactions, and consequently improves the device performance. The other one is to attach different electron acceptor units at the terminal of the molecules, including: dicyanovinyl [20–21], cyanoacetate [20–23], rhodanine [8,14,17,19,23], 1,3-indandione [16], and diketopyrolpyrol (DPP) moieties [24–25]. Changing the electron-withdrawing strength of the terminal electron acceptor unit, on the other hand, will change the intramolecular charge transfer state and tune the light absorption ability, which will consequently change the photovoltaic performance of the materials as well.…”

“…In this respect, oligothiophenes, including monotiophene [16,20], bithiophene [16], terthiophene [8,14–15 17–19 21–23 26], quaterthiophene and quinquethiophene [27], and cyclopentadithiophene [28] have been utilized as the π-bridge in constructing conjugated molecules with a BDT core. Among these 3,3''-dihexyl-2,2':5':2''-terthiophene (3T) is the most widely used π-bridge.…”