Attaining a Remarkable Efficiency of 11.57% in a Polymer Solar Cell Submodule with a 55 cm² Active Area using 1D/2A Terpolymers and Nonhalogenated Solvents

Polymer solar cells (PSCs) employing a bulk heterojunction structure exhibit a significant potential as energy sources for advanced portable electronic devices due to their low weight, scalable roll-to-roll (R2R) processing, and cost-effectiveness. Recent advances in the design of high-performance photoactive materials and device structure optimization, have resulted in a remarkable increase in the power conversion efficiency (PCE) of PSCs, surpassing 19 %. Recently, the PM6 copolymer has been widely used in the photoactive layers of PSCs due to its high crystallinity, superior hole mobility, and strong pre-aggregation behavior. However, achieving high-performance PSCs based on the PM6 polymer normally requires the use of halogenated solvents such as chloroform and chlorobenzene. Unfortunately, the use of these halogenated solvents is limited in mass production because of environmental toxicity concerns. Furthermore, due to the strong temperature dependent aggregation property of the PM6 polymer, PM6-based large-area PSCs fabricated using large-scale coating methods exhibits a significant reduction in PCE. For example, PM6-based small-area (0.12 cm2) PSCs exhibits a PCE of 15.1 %. However, the PCE of PM6-based large-area (54.5 cm2) PSC submodules can be significantly reduced to 8.73 %. This decrease in performance of PM6-based large-area PSCs in nonhalogenated systems can be attributed to the oversized domains and nonuniformity in the photoactive layer, leading to an increased cell-to-module (CTM) loss. The undesirable morphology of the PM6-based photoactive layer can be controlled using a high-temperature (HT) process such as a hot solution and/or preheated substrates. However, such a complicated process is unsuitable for the production of cost effective and highly reproducible R2R PSC modules. Therefore, it is necessary to develop new p-type polymer for high-performance large-area PSC modules based on simple processes and minimize the CTM loss in nonhalogenated systems.<br/>Terpolymers composed of three different monomers have recently attracted attention as promising p-type polymer. Terpolymers can accurately control physicochemical properties, such as frontier energy levels, light harvesting ability, pre-aggregation behavior, miscibility, and crystallinity, by introducing a third component directly into the donor-acceptor (D-A) copolymer backbone.<br/>Herein, we synthesize a new series of 1D/2A terpolymers for developing room-temperature (RT) and nonhalogenated solvent processed high-performance PSCs submodules. The terpolymers are composed of three components: benzo[1,2-b:4,5-b']dithiophene (BDT-F), thieno[3,4-c]pyrrole-4,6(5H)-dione (TPD-TT), and benzo-[1,2-c:4,5-c']dithiophene-4,8-dione (BDD). Three PBTPttBD terpolymers (i.e. PBTPttBD-25, PBTPttBD-50, and PBTPttBD-75) are synthesized using different ratios TPD-TT to BDD composition ratios, corresponding to TPD-TT contents of 25 %, 50 %, and 75 %, respectively. The composition ratio of the TPD-TT and BDD components can be used to control the light harvesting ability, energy level, molecular ordering, and charge transport properties of the PBTPttBD polymers. A grazing incidence wide-angle X-ray scattering and contact angle analysis shows that the PBTPttBD-75:BTP-C11 blended film exhibits a predominant face-on orientation with good miscibility. The RT and nonhalogenated solvent processed PBTPttBD-75:BTP-eC11 PSC exhibit a high PCE of 15.55 %. Furthermore, PBTPttBD-75:BTP-eC11-based PSC submodules, processed with <i>o</i>-xylene under RT conditions, achieve a notable PCE of 11.57 % over a 55 cm2 active area. This PCE value is among the highest reported in single-junction PSC submodules processed with nonhalogenated solvent.