Intrinsically Stretchable and Non‐Halogenated Solvent Processed Polymer Solar Cells Enabled by Hydrophilic Spacer‐Incorporated Polymers

Abstract

Blends of polymer donors (PDs) and small molecule acceptors (SMAs) have afforded highly efficient polymer solar cells (PSCs). However, most of the efficient PSCs are processed using toxic halogenated solvents, and they are mechanically fragile. Here, a new series of PDs by incorporating a hydrophilic oligo(ethylene glycol) flexible spacer (OEG‐FS) is developed, and efficient PSCs with a high power conversion efficiency (PCE) of 17.74% processed by a non‐halogenated solvent are demonstrated. Importantly, the incorporation of these OEG‐FSs into the PDs significantly increases the mechanical robustness and ductility of resulting PSCs, making them suitable for application as stretchable devices. The OEG‐FS alleviates excessive backbone rigidity of the PDs while enhancing their pre‐aggregation in the non‐halogenated solvent. In addition, the OEG‐FS in the PDs enhances PD‐SMA interfacial interactions and improves blend morphology, resulting in efficient charge generation and mechanical stress dissipation. The resulting PSCs demonstrate a superior PCE (17.74%) and high crack‐onset strain (COS = 10.50%), outperforming the PSCs without OEG (PCE = 15.64% and COS = 2.99%). Importantly, intrinsically stretchable (IS) PSCs containing the PD featuring OEG‐FS exhibit a high PCE (12.05%) and stretchability (maintaining 80% of the initial PCE after 22% strain), demonstrating their viability for wearable applications.

Development of rigidity-controlled terpolymer donors for high-performance and mechanically robust organic solar cells

“…This result can be attributed to the fact that the mechanical properties of the blend films are determined by both the tensile properties of each constituent and their interfacial properties. 12,20 For example, superior mechanical properties of PM6-B10:Y6-BO and PM6-B20:Y6-BO blend films are attributed to the synergistic effect of better tensile properties of their terpolymer donors and more developed intermixing of their P D and S A domains that suppresses crack formation/propagation.…”

“…, PM6 with 4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2- b :4,5- b ′]dithiophene (FBDT) and 1,3-bis(2-ethylhexyl)-5,7-di(thiophen-2-yl)-4 H ,8 H -benzo[1,2- c :4,5- c ′]dithiophene-4,8-dione (DTBDD) units) to facilitate π–π intermolecular assembly and enhance electrical properties, however, their mechanical properties in films including tensile properties are poor. 9–12…”

“…In order to enhance the mechanical properties of P D s, the high molecular rigidity of polymer chains should be reduced by increasing the chain flexibility. 12–17 A promising strategy to achieve this end is the introduction of flexible spacers through terpolymerization. 12,18–20 For example, Thompson et al reported that a terpolymer (10% T-10-T) with decyl spacers demonstrates an 8-fold increased crack onset strain (COS) than a corresponding polymer without decyl spacers.…”

“…12–17 A promising strategy to achieve this end is the introduction of flexible spacers through terpolymerization. 12,18–20 For example, Thompson et al reported that a terpolymer (10% T-10-T) with decyl spacers demonstrates an 8-fold increased crack onset strain (COS) than a corresponding polymer without decyl spacers. 19 However, the presence of such electro-inactive spacers in P D s often impairs their electrical properties ( i.e.…”

Composition-Tolerant Terpolymers for Efficient, Nonhalogenated Solvent-Processed Polymer Solar Cells

“…The terpolymerization approach involves incorporating a third molecular building block into donor–acceptor alternating copolymers as a property modifier, by which various properties of conjugated polymers, such as crystallinity, light harvesting characteristics, and energy levels, are finely modulated on-demand. − Therefore, terpolymerization approaches have been widely used in polymer solar cell (PSC) research and proved to be effective in enhancing device performance. For example, the high power conversion efficiencies (PCEs), achieved based on alternating copolymer-type polymer donors ( P D s) or polymer acceptors ( P A s), − have been further increased using terpolymerization approaches to improve their light absorption characteristics and to fine-tune their frontier orbital energy levels. − In addition, the mechanical and thermal stabilities of PSCs have been effectively optimized using a terpolymerization approach. ,− Another important contribution of terpolymerization approaches is to fine-tune the solubility and aggregation properties of P D s, enabling the eco-friendly fabrication of PSCs, i.e., obviating the need for toxic halogenated solvents during device manufacturing. − For instance, Hou et al developed a terpolymer series (T1, T2, and T3) in which a certain fraction of BDD units were replaced with ethyl thiophene-3-carboxylate units to realize P D s with significantly increased solubility in tetrahydrofuran .…”