Molecular Orientation Unified Nonfullerene Acceptor Enabling 14% Efficiency As‐Cast Organic Solar Cells

Abstract

Molecular orientation and π-π stacking of nonfullerene acceptors (NFAs) determine its domain size and purity in bulk-heterojunction blends with a polymer donor. Two novel NFAs featuring an indacenobis(dithieno[3,2-b:2′,3′-d] pyrrol) core with meta-or para-alkoxyphenyl sidechains are designed and denoted as m-INPOIC or p-INPOIC, respectively. The impact of the alkoxyl group positioning on molecular orientation and photovoltaic performance of NFAs is revealed through a comparison study with the counterpart (INPIC-4F) bearing para-alkylphenyl sidechains. With inward constriction toward the conjugated backbone, m-INPOIC presents predominant face-on orientation to promote charge transport. The as-cast organic solar cells (OSCs) by blending m-INPOIC and PBDB-T as active layers exhibit a power conversion efficiency (PCE) of 12.1%. By introducing PC 71 BM as the solid processing-aid, the ternary OSCs are further optimized to deliver an impressive PCE of 14.0%, which is among the highest PCEs for as-cast single-junction OSCs reported in literature to date. More attractively, PBDB-T:m-INPOIC:PC 71 BM based OSCs exhibit over 11% PCEs even with an active layer thickness over 300 nm. And the devices can retain over 95% of PCE after storage for 20 days. The outstanding tolerance to film thickness and outstanding stability of the as-cast devices make m-INPOIC a promising candidate NFA for large-scale solutionprocessable OSCs.

Heating induced aggregation in non-fullerene organic solar cells towards high performance

“…The chemical structures and energy levels of the donor polymer PBDB-T and NFA m-INPOIC investigated in this work are shown in Fig. 1(a) [28,41]. By leveraging the unique temperature-dependent aggregation property of PBDB-T and longer relaxation time of polymer chains [28,40], the heating-induced-aggregation (HIA) strategy could effectively manipulate the confinement effects of PBDB-T aggregates on the p-p packing of m-INPOIC molecules.…”

“…m-INPOIC was synthesized in our previous work [41]. Donor polymer PBDB-T was purchased from Solarmer Materials (Beijing) Inc. ZnO precursor was prepared by dissolving 200 mg zinc acetate dehydrate (Zn(CH 3 COO) 2 Á2H 2 O, 99.9%, Aldrich) and 0.056 ml of ethanolamine in 2 ml of 2-methoxyethanol.…”

Recent Progress of Organic Solar Cells with Insulating Polymers

“…Based on these requirements, the novel materials used as the donor (D), acceptor (A), or transportation layer are synthesized and exhibit excellent device performance. [13][14][15] To further improve PCE, the ternary OSC strategy was proposed to achieve better performance via broadening absorption, energy cascade, energy transfer, and parallel or alloy models. [16][17][18][19] Conventional additives, 1,8-diodooctane (DIO) and 1-chloronapthalene (CN), can facilitate crystallization and the formation of a fibril network and thereby accelerate charge transportation.…”

Efficient As‐Cast Polymer Solar Cells with High and Stabilized Fill Factor

“…[ 17,24–26 ] Thus, in as‐cast NFA‐based PSCs without the need of post‐treatment, it is essential to synthesize NFAs with high molecular ordering, by manipulating side chains, extending effective conjugation, and enhancing π–π interaction of end groups. [ 19,27–33 ] Thus far, the best PCE reported in the literature for as‐cast PSCs based on newly designed NFAs with a high boiling point processing solvent is 14.0%, using the ternary strategy. [ 31,32 ] In as‐cast PSCs, alkyl‐substituted NFAs could enhance intermolecular interaction and consequently reduce the π–π spacing.…”

“…[ 19,27–33 ] Thus far, the best PCE reported in the literature for as‐cast PSCs based on newly designed NFAs with a high boiling point processing solvent is 14.0%, using the ternary strategy. [ 31,32 ] In as‐cast PSCs, alkyl‐substituted NFAs could enhance intermolecular interaction and consequently reduce the π–π spacing. However, without the steric hindrance of the bulky aryl side group, the possibility to form H‐type π–π stacking increases, while J‐type π–π stacking is preferred to ensure charge transport in the NFA domain.…”