Ambipolar Low-bandgap Copolymers Consisting of Dithienoketopyrrole for All-Polymer Solar Cells

Abstract

The new low-band gap copolymers containing electron-accepting thienoisoindigo (TIDG) exhibit the low-lying lowest unoccupied molecular orbital (LUMO) at-3.8 eV. This envisions their use as n-type polymer in combination with typical p-type regioregular poly(3-hexylthiophene) (P3HT) towards all-polymer organic photovoltaics (OPV). The alternating fluorene and TIDG copolymer, PFTIDG, shows the electronic absorption maximum at 744 nm in the film states, of which spectrum is complementary to that of P3HT and thus advantageous for covering the wide solar spectrum. The laser and Xe-flash time-resolved microwave conductivity (TRMC) evaluations were performed for screening the effects of p/n blend ratio and thermal annealing in bulk heterojunction framework. The power conversion efficiency of 0.06% was obtained for pre-annealed P3HT:PFTIDG = 1:1 together with a high open circuit voltage of 0.92 V, which is suggestive of ambipolar characteristics of PFTIDG.

Design and structure–property relationship of benzothienoisoindigo in organic field effect transistors

“…In contrast, thienoisoindigo (TII), in which the benzene rings of the II unit are replaced with thiophenes, is a completely planar unit since the non-bonding sulfur-oxygen interaction removes the steric hindrance to form a at p-surface and enhance the charge delocalization coming from the quinoidal structure of the framework. 8,[23][24][25][26][27][28][29][30][31][32][33][34][35] In a previous study, we reported ambipolar TII-based small molecules, and these molecules displayed wellbalanced hole and electron mobilities of 10 À2 cm 2 V À1 s À1 in spite of the one-dimensional p-system. 28 These results prompted us to design a more p-expanded TII-based molecule, benzothienoisoindigo BTII, to ensure strong p-p intermolecular interactions constructing a dense molecular packing preferable for effective charge-transport.…”

“…14,15 However, the ambipolar properties of small molecules are still lower than those of polymer semiconductors. 8,[23][24][25][26][27][28][29][30][31][32][33][34][35] In a previous study, we reported ambipolar TII-based small molecules, and these molecules displayed wellbalanced hole and electron mobilities of 10 À2 cm 2 V À1 s À1 in spite of the one-dimensional p-system. [16][17][18][19][20][21] Among the building blocks constituting organic semiconductors, isoindigo (II) is well known as an electron-decient unit realizing a high performance OFET.…”

Study of Photoelectric Conversion in Benzotrithiophene-Based Conjugated Semiconducting Polymers

“…Xe-flash time-resolved microwave conductivity (Xe-TRMC, 9 GHz) 27) experiment using a pseudo-sunlight white light pulse (0.3 mJ cm -2 pulse -1 ) as an excitation was conducted in order to study the photovoltaic performance of polymer: [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 61 BM, purchased from Frontier Carbon Inc.) blends prior to device fabrication. 24,[28][29][30][31] The blend samples were prepared by drop-casting chlorobenzene (CB) solution of polymer:PC 61 BM onto quartz plate and dried under vacuum. The photoconductivity was obtained by P r /AP r , where P r , A, and P r , are the transient power change of reflected microwave power, sensitivity factor, and reflected microwave power, respectively.…”

Control of Phase Separation of Benzothienoisoindigo-Benzodithiophene Copolymer for Organic Photovoltaics

“…TIDG demonstrates a high planarity and strong electron affinity in nature, which allows extending photoabsorption to near infrared region [15], and thus, TIDG is attempted to be coupled with various donor units [20][21][22][23]. The constrained low PCEs are partly ascribed to the short lifetime of singlet exciton [16] associated with energy gap law [24].…”