Location and Number of Selenium Atoms in Two-Dimensional Conjugated Polymers Affect Their Band-Gap Energies and Photovoltaic Performance

Abstract

We synthesized and characterized a series of novel twodimensional Se-atom-substituted donor (D)−π-acceptor (A) conjugated polymersPBDTTTBO, PBDTTTBS, PBDTTSBO, PBDTSTBO, PBDTTSBS, PBDTSTBS, PBDTSSBO, and PBDTSSBSfeaturing benzodithiophene (BDT) as the donor, thiophene (T) as the π-bridge, and 2,1,3benzooxadiazole (BO) as the acceptor with different number of Se atoms at different π-conjugated locations, including the π-bridge, side chain, and electron-withdrawing units. We then systematically investigated the effect of different locations and the number of Se atoms in these two-dimensional conjugated polymers on the structural, optical, and electronics such as bandgap energies of the resulting polymers, as determined through quantumchemical calculations, UV−vis absorption spectra, and grazing-incidence Xray diffraction. We found that through the rational structural modification of the 2-D conjugated Se-substituted polymers the resulting PCEs could vary over 3-fold (from 2.4 to 7.6%), highlighting the importance of careful selection of appropriate chemical structures such as the location of Se atoms when designing efficient D−π-A polymers for use in solar cells. Among these tested BO-containing polymers, PBDTSTBO that has moderate band gaps and good open-circuit voltages (up to 0.86 V) when mixed with PC 71 BM (1:2, w/w) provided the highest power conversion efficiency (7.6%) in a single-junction polymer solar cell, suggesting that these polymers have potential applicability as donor materials in the bulk heterojunction polymer solar cells.

Silafluorene‐based polymers for electrochromic and polymer solar cell applications

“…In addition, lower E ox,onset values were also recorded for selenophene bearing derivatives which is consistent with previous discussions in literature . HOMO–LUMO energy levels of the polymers were determined using the oxidation and reduction onset values calculated from CV.…”

Side chain engineering and conjugation enhancement of benzodithiophene and phenanthrenequnioxaline based conjugated polymers for photovoltaic devices

“…D‐A copolymer can provide strong intramolecular charge transfer (ICT), which can tune the energy level, enhance the light absorption ability and improve the charge mobility . To further explore strategies to improve solar cell performance, two dimensional(2D) D‐A conjugated polymers with conjugated side chains have been synthesized and studied . Due to the enhanced conjugation, the 2D conjugated polymer possesses more interchain π−π overlaps and consequently shows broad absorption bands .…”

Modified structure of two-dimensional polythiophene derivatives by incorporating electron-deficient units into terthiophene-vinylene conjugated side chains and the polymer backbone: synthesis, optoelectronic and self-assembly properties, and photovoltaic application

“…30,34,[53][54][55] The morphology of photoactive layer plays a decisive role in determining the photovoltaic characteristics of PSC devices. [56][57][58] Herein, atomic force microscopy (AFM) was used to investigate the morphologies of the spin-coated lms of polymers/PC 61 BM on top of ITO/PEDOT:PSS, which were prepared by using the same procedure and parameters for preparing the photoactive layers. As shown in Fig.…”