Unprecedented Long‐Term Thermal Stability of 1D/2A Terpolymer‐Based Polymer Solar Cells Processed with Nonhalogenated Solvent

Abstract

Donor–acceptor (D–A) copolymer‐based polymer solar cells (PSCs) processed with nonhalogenated solvents exhibit relatively low power conversion efficiencies (PCE) due to undesirable morphological properties, including high aggregation and unfavorable orientation. Moreover, they show very poor long‐term stability owing to excessive molecular aggregation and unfavorable phase separation. Thus, novel p‐type polymers are required for high‐efficiency and long‐lived PSCs that can be processed in ecofriendly nonhalogenated solvents. Herein, a novel series of 1D/2A terpolymers (PBTPBD) composed of 4,8‐bis(5‐(2‐ethylhexyl)‐4‐fluorothiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDT‐F), 1,3‐bis(thiophen‐2‐yl)‐5,7‐bis(2‐ethylhexyl)benzo‐[1,2‐c:4,5‐c′]dithiophene‐4,8‐dione (BDD), and 1,3‐bis‐(4‐hexylthiophen‐2‐yl)‐5‐octyl‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (HT‐TPD) is synthesized and characterized for high‐efficiency and long‐lived PSCs. A PBTPBD‐50:IT‐4F blended film exhibits a favorable face‐on orientation and superior hole and electron mobility. Therefore, the corresponding PBTPBD‐50:IT‐4F PSC, processed with a nonhalogenated solvent, exhibits a high PCE of 13.64%, which is 13% higher than that of the related nonhalogenated solvent‐processed PSCs. Furthermore, the PBTPBD‐50:IT‐4F PSC maintains 82% of the initial PCE even after 204 days at 85 °C, which is the highest thermal stability achieved among PSCs processed with nonhalogenated solvents. The high‐efficiency and superior long‐term thermal stability of the PBTPBD‐50:IT‐4F PSC are attributed to the excellent miscibility of PBTPBD‐50 and IT‐4F and the suppression of the morphological changes in the photoactive layer.

Side‐chain engineering of regioregular copolymers for high‐performance polymer solar cells processed with nonhalogenated solvents

“…Absorption peaks from 500 to 700 nm can be attributed to intermolecular charge transfer (ICT) between donor and acceptor units. [30][31][32][33][34] The solution and film absorption spectra of rr-PfBT2f4T-2OD and rr-PfBT2f4T-2DT showed similar UV-vis profiles with strong vibronic shoulder peaks. Moreover, both polymers exhibited almost identical maximum absorption peaks in solution and film states, indicating that pre-aggregation occurs in solution state.…”

Tradeoff between Intermolecular Interaction and Backbone Disorder by High Molecular Dipole Block for Improving Blend Morphology of Polymer Solar Cells

“…[21,27,33,34] Additionally, molecular dipole interaction was also proved effective to influence the intermolecular interaction of the terpolymers. [35] This is because the BDD unit possesses a rather low dipole moment for its symmetric aromatic structure. Thus, choosing an A 2 group with suitable dipole moment to offset the effect of entropy increment shall be an elegant method to obtain a desired morphology.…”

Green‐Solvent‐Processed 17% Efficient Polymer Solar Cell Achieved Synergistically by Aligning Energy Levels and Improving Morphology with the Quaternary Strategy

“…However, these solvents are detrimental to human health and the environment, and are not adaptable for industrial production due to their toxic nature and high volatility. [ 43–48 ]…”

“…However, these solvents are detrimental to human health and the environment, and are not adaptable for industrial production due to their toxic nature and high volatility. [43][44][45][46][47][48] Therefore, efforts have been made to seek photovoltaic material systems which are suitable for fabricating high-efficiency PSCs with non-halogenated solvents. Huang et al reported a new non-fullerene acceptor DTY6 by employing the long branched alkyl chains (2-decyltetradecyl, 2-DT) to replace the 2-ethylhexy on dithie-nothiophen[3.2-b]pyrrolobenzothiadiazole (TPBT) central unit of Y6.…”