Elevated Photovoltaic Performance in Medium Bandgap Copolymers Composed of Indacenodi-thieno[3,2-b]thiophene and Benzothiadiazole Subunits by Modulating the π-Bridge

Abstract

Two random conjugated polymers (CPs), namely, PIDTT-TBT and PIDTT-TFBT, in which indacenodithieno[3,2-b]thiophene (IDTT), 3-octylthiophene, and benzothiadiazole (BT) were in turn utilized as electron-donor (D), π-bridge, and electron-acceptor (A) units, were synthesized to comprehensively analyze the impact of reducing thiophene π-bridge and further fluorination on photostability and photovoltaic performance. Meanwhile, the control polymer PIDTT-DTBT with alternating structure was also prepared for comparison. The broadened and enhanced absorption, down-shifted highest occupied molecular orbital energy level (EHOMO), more planar molecular geometry thus enhanced the aggregation in the film state, but insignificant impact on aggregation in solution and photostability were found after both reducing thiophene π-bridge in PIDTT-TBT and further fluorination in PIDTT-TFBT. Consequently, PIDTT-TBT-based device showed 185% increased PCE of 5.84% profited by synergistically elevated VOC, JSC, and FF than those of its counterpart PIDTT-DTBT, and this improvement was chiefly ascribed to the improved absorption, deepened EHOMO, raised μh and more balanced μh/μe, and optimized morphology of photoactive layer. However, the dropped PCE was observed after further fluorination in PIDTT-TFBT, which was mainly restricted by undesired morphology for photoactive layer as a result of strong aggregation even if in the condition of the upshifted VOC. Our preliminary results can demonstrate that modulating the π-bridge in polymer backbone was an effective method with the aim to enhance the performance for solar cell.

Fluorination Effect for Highly Conjugated Alternating Copolymers Involving Thienylenevinylene-Thiophene-Flanked Benzodithiophene and Benzothiadiazole Subunits in Photovoltaic Application

“…In detail, the 9 nm blue-shifted value (383-392 nm) for π-π* peak, 15 nm (from 648 to 663 nm) and only 5 nm (from 712 to 717 nm) red-shifted values for corresponding ICT and shoulder peaks were observed, whereas the 8 and 0 nm blue-shifted values and a newly emerged peak at 508 nm due to the π-π* transition, both 15 nm red-shifted values (from 600 to 615 nm and from 648 to 663 nm) for ICT and shoulder peaks were also observed in fluorinated PBDT-TVT-FBT, ongoing from solution to film state. The blue-shifted absorption spectra were observed after fluorination both in CB solution and solid film, which were identical with the results observed in DTBDT-TIPS-alt-BT and naphthobisthiadiazole-alt-bithiophene system [88,95]. Furthermore, the onsets of the optical absorptions for PBDT-TVT-BT and PBDT-TVT-FBT films were found to be 775 nm (E opt g = 1.60 eV) and 735 nm (E opt g = 1.69 eV), respectively.…”

“…1 H NMR spectra; melting points test; C, H, and N elemental analyses; TGA analyses; molecular weights of polymer; UV-Vis absorption; electrochemical cyclic voltammetry (CV); thin film X-ray diffraction (XRD); atomic force microscopy (AFM); and transmission electron microscopy (TEM) images were obtained according to our reported methods [86][87][88][89].…”

“…Recently, our group developed a 4,5-didecyl-thienylenevinylene thiophene (DR-TVT) modified BDT-containing CPs and investigated the effect of electron withdrawing [63]. As for the various electron-acceptor units utilized, benzo[c] [1,2,5]-thiadiazole (BT) and its derivatives were considered as the stronger electron-withdrawing moieties and tremendous BT-based semiconducting materials have been focused on, because of subtly integrating its electron accepting property and its ability to adopt the quinoid structure, easy availability, and modification [7,20,21,24,28,35,37,41,42,47,49,50,58,63,64,73,[84][85][86][87][88].…”

1,4-Bis((9H-Carbazol-9-yl)Methyl)Benzene-Containing Electrochromic Polymers as Potential Electrodes for High-Contrast Electrochromic Devices

“…Nowadays, the most popular π–conjugated polymers (e.g., polythiophenes [ 18 ], polyaniline [ 19 , 20 ], polyindoles [ 21 ], polycarbazole [ 22 , 23 ], polyfurans [ 24 ], polypyrenes [ 25 ], and PEDOT-PSS [ 26 ]) are widely applied to organic electrochromic devices. Among the many promising π–conjugated polymers, carbazole-containing polymers have attractive optoelectronic properties due to their hole-transporting characteristics via the radical cation and dication species as well as their ease of oxidation through the nitrogen centers.…”

Appropriate Molecular Interaction Enabling Perfect Balance Between Induced Crystallinity and Phase Separation for Efficient Photovoltaic Blends

“…For solving energy dilemma, polymer solar cells (PSCs) evolved as a prevalent technology because of their unique peculiarity of low toxicity and the potential in fabricating flexible devices. − Many breakthroughs with power conversion efficiency (PCE) surpassing 17% have been reached with the prosperous evolution of non-fullerene acceptors (NFAs) because of the advantages of their highly tunable optoelectronic properties. − Notably, elaborately designing photovoltaic materials could profoundly determine the coverage of the solar spectrum and the transport of charge carriers. Introducing the fluorine (F) atom into a donor or an acceptor is deemed as an effectual strategy in fabricating high-performance PSCs as the fluorination could effectively adjust the electronic orbital and optical band gap, which could dissociate the exciton and obtain high open-circuit voltage ( V OC ). − Hou designed PM6 by modifying the side chain of PBDTBDD with a fluorine atom.…”