A strong influence of the positions of solubilizing alkyl side chains on optoelectronic and photovoltaic properties of TTBTBTT-based conjugated polymers

Abstract

We report the synthesis and comparative study of five conjugated polymers P1-P5 with different arrangements of two solubilizing 2-ethlyhexyl side chains in their repeating units. It has been shown that positioning of the alkyl substituents affects strongly frontier energy levels of the polymers and results in variation of their optical band gaps between 1.65 and 2.0 eV. The highest (2.8×10 -4 cm 2. V -1. s -1 ) and the lowest (2.4×10 -5 cm 2. V -1. s -1 ) charge carrier mobilities determined for the polymers P1 and P5, respectively, using SCLC technique differ by more than one order of magnitude. GIWAXS measurements also revealed very different degrees of molecular ordering in the films of polymers P1-P5 which correlate well with the SCLC mobility data and solid state photoluminescence spectra of these materials. The bulk heterojunction solar cells based on the composites of polymers P1-P5 with [60]PCBM demonstrated power conversion efficiencies ranging from 0.6% (P5) to 5.1% (P1) thus evidencing strong influence of the alkyl side chains on the photovoltaic performance of the designed polymer-based materials. This journal is Electronic Supplementary Information (ESI) available: Optical absorption spectra for thin films, cyclic voltammograms, J 1/2 -V plots for hole-only This journal is ARTICLE Journal Name devices, 2D GIWAXS patterns for thin films of P1-P5, AFM images for composites of P1-P5 with [60]PCBM. See

Solubilized 5,6-bis(octyloxy)benzoxadiazole as a versatile acceptor block for designing novel (-X-DADAD-)n and (-X-DADADAD-)n electron donor copolymers for bulk heterojunction organic solar cells

“…4; the corresponding data for the polymer-PC 61 BM composite systems are presented in ESI. It is seen from Table 2 that the solar cells based on P1-P3 exhibit high open circuit voltages outperforming significantly devices based on the previously reported benzothiadiazole analogues (V OC ¼775 mV) [12,13,14]. This result confirmed our initial hypothesis that the material HOMO energy can be lowered and the open circuit voltage of photovoltaic cells can be improved by replacing benzothiadiazole acceptor (A) units with benzoxadiazole in the (-X-DADAD-) n polymers.…”

“…13 Synthesis of 6: A mixture of 3 (0.500 g, 0.43 mmol), 2-(tributylstannyl)thiophene (0.650 g, 1.76 mmol) and Pd(PPh 3 ) 4 (0.020 g, 0.02 mmol) was dissolved in 50 mL of toluene, deaerated and heated at reflux for 6 h. Then the solvent was removed at the rotary evaporator and the residue was washed with ethanol. 13 …”

“…In particular, conjugated polymers comprising carbazole (X) moieties bearing solubilizing alkyl chains, thiophene (T) donor units (D) and benzothiadiazole (BT) acceptor fragments (A) were reported [12,13]. The application of the extended T-BT-T-BT-T building block (as compared to the conventional T-BT-T) allowed us to reduce significantly the energy band gap of the resulting polymer (from 1.90 to 1.65 eV) while keeping the HOMO level almost unchanged ( À 5.50 eV vs. À 5.44 eV).…”

Impact of Alkyl Side Chains on Optoelectronic and Photovoltaic Properties of Novel Benzodithiophenedione‐Based Conjugated Polymers

“…Recently, we reported a new approach to design (X‐DADAD) n polymers, which show improved optoelectronic properties in comparison with the well‐known (X‐DAD) n macromolecular structures . According to the Scharber theoretical model, this type of donor materials can provide 13%–15% efficiency in single‐junction OSCs .…”

Research in the Field of Organic Photovoltaics at the Institute for Problems of Chemical Physics of Russian Academy of Sciences

“…23) [150]. It should be emphasized that these polymers differ only by the attachment positions of the solubilizing alkyl side chains in the polymer backbone.…”