Understanding of Imine Substitution in Wide-Bandgap Polymer Donor-Induced Efficiency Enhancement in All-Polymer Solar Cells

Abstract

All-polymer solar cells (all-PSCs) are proven to possess outstanding thermal and mechanical stabilities. However, concurrently achieving appropriate phase-separated pattern, efficient charge transportation, and adequate charge transfer between donor and acceptor components is still a challenge, and thus, only a few polymer−polymer bulk heterojunction (BHJ) blends have yielded BHJ device power conversion efficiency (PCE) values of >8%. Generally, polymer backbone substitutions may have a direct influence on the device performance. Thus, this report examines a set of wide bandgap polymer donor analogues composed of thienothiophene (TT) or thiazolothiazole (TTz) motif, and their all-PSC device performance with N2200. Results show that all-PSCs based on the imine-substituted derivative PBDT-TTz exhibit PCE values as high as 8.4%, which largely outperform the analogue PBDT-TT-based ones with PCEs of only 0.7%. This work reveals that the imine substitution in polymer backbones of PBDT-TTz not only increases the ionization potential (IP) and electron affinity (EA), narrows the optical gap (E opt ), but also has significantly impacts on the BHJ film morphologies. PBDT-TTz:N2200 BHJ blends present better miscibility, suppressed phase separation, much stronger crystallinity, and face-on ordering, which contribute to efficient exciton dissociation, charge transportation, and therefore, high-efficiency in all-PSCs. This study demonstrates that the iminesubstituted polymers composed of TTz motif, which can be easily synthesized through a facile two-step procedure, are a promising class of wide-bandgap polymer donors for efficient all-PSCs.

Obtaining Reversible, High Contrast Electrochromism, Electrofluorochromism, and Photochromism in an Aqueous Hydrogel Device Using Chromogenic Thiazolothiazoles

“…[ 19 ] In addition, environmentally sensitive asymmetric TTz derivatives can serve as molecular probes for cell imaging and cell membrane voltage sensing. [ 33 ] The excellent electronic and optical properties of TTz‐based materials have enabled them to be studied in a variety of molecular electronic applications such as organic photovoltaics (OPVs), [ 34 ] organic field‐effect transistors (OFETs), [ 35–37 ] organic light‐emitting diodes (OLEDs), [ 38 ] metal‐organic framework/covalent‐organic framework materials, [ 39–42 ] and redox flow batteries. [ 43 ] Herein, multifunctional chromogenic devices (CGDs) (electrochromic, EFC, and photochromic) are demonstrated using extended TTz viologens developed for low cost, non‐toxic, and water‐based hydrogel devices.…”

A New Ester‐Substituted Quinoxaline‐Based Narrow Bandgap Polymer Donor for Organic Solar Cells

“…[ 1 ] Generally, to make full use of solar energy in OSCs, different donors, including wide bandgap, medium bandgap, and narrow bandgap (NBG) donor materials, are developed to match well with different acceptors. [ 2 ] Among these donors with different bandgaps, the NBG polymers have some intrinsic characteristics, for instance, the optical absorption of NBG polymers can reach to the near‐infrared (NIR) region, hence, more sunlight photons can be harvested when NBG donors are paired with fullerene derivative acceptors. [ 3 ]…”

Highly Efficient All‐Polymer Solar Cells Processed from Nonhalogenated Solvents

“…Recently, thiazolothiazole (TTz)-based polymer donors have yielded impressive performance in OSCs owing to its coplanar backbone, wide-bandgap, appropriate FMOs, and large holetransport character. [46][47][48] For example, Zhang and co-workers developed a polymer donor poly [4,8- [5,4-d]thiazole] (PSTZ) with a wide-bandgap of 1.96 eV and deep-lying highest occupied molecular orbital (HOMO) of À 5.44 eV, which has exhibited a high PCE of 11.1 % when mingled with two compatible FREAs (i. e., IDIC and ITIC). [47] In addition, Cao et al also reported the similar polymer donor PBDT-TTz to afford high PCE of 8.4 % in all-PSC devices when blended with benchmark N2200.…”