Design of Nonfused Nonfullerene Acceptors Based on Pyrido- or Benzothiadiazole Cores for Organic Solar Cells

Abstract

Nonfullerene acceptors (NFAs) have received tremendous attention due to their significant contributions to the field of organic solar cells (OSCs). However, the synthetic complexities of large fused-ring conjugated structures in typical NFAs limit their commercial applicability. Thus, a low-cost design strategy with synthetic simplicity and admirable absorption characteristics is highly desirable. In the present work, we report the synthesis of two nonfused NFAs, namely,2,2,5] , based on altering the central acceptor core (A′) with a pyrido-or benzothiadiazole (PT/BT) ring, keeping identical donor (D) bridges and end-capping acceptors (A's). The tuning of the central core with PT/BT altered the optical properties, highest occupied molecular orbital (HOMO)−lowest unoccupied molecular orbital (LUMO) energy levels, and fine-tuning in the molecular crystallinities. Moreover, a significant difference in the photovoltaic performance with decent power conversion efficiencies of 6.6% and 9.3% was achieved by WHC-1 and WHC-4, respectively, using a well-known polymer donor PM6. The results demonstrated the utility of A−D−A′−D−A type nonfused NFAs with broadband absorption spanning from 300 to 960 nm for high-performance OSCs. Furthermore, the scope of the development in A−D−A′−D−A type NFAs using appropriate building blocks can lead to a great breakthrough in OSCs.

Recent progress in non-fused ring electron acceptors for high performance organic solar cells

“…57 Thus, when using PM6 as a donor, the device of WHC-1 showed a lower PCE of 6.6% than the WHC-4 based device (9.3%), which is mainly attributed to the lower V oc of the WHC-1 based device. 59 Compared with the BT unit, the BTz unit shows a relatively weak electron-withdrawing ability and can provide an additional functionalization site on the 2-position of the triazole. 18 Thus the energy levels, solubilities and packing modes of the molecules incorporating the BTz unit can be efficiently modulated.…”

Low-cost synthesis of small molecule acceptors makes polymer solar cells commercially viable

“…Polymer solar cells (PSCs) have drawn extensive research attentions in recent years, due to their advantages of light weight, flexibility, low-cost and large-area solution processing 1 – 4 . Recently, the power conversion efficiencies (PCEs) of PSCs have reached over 18% 5 – 11 ,which is mainly benefited from the emerging narrow-bandgap small molecule acceptors (SMAs) with attractive advantages of easily adjustable structures, strong absorption in the near−infrared region and lower photon energy loss during photocurrent generation 3 , 12 – 15 . With the PCE of PSCs approaching the commercially viable efficiencies, increased attention has been paid to the cost of the photovoltaic materials 16 .…”

Naphthobistriazole based non-fused electron acceptors for organic solar cells

“…24 IC-acceptor based fused-ring cores represent the highest performance in OSCs due to the controlled microstructures via large conjugated backbones as well as large steric hindrance, but their high synthetic complexity enhances the cost toward manufacture. As an alternative, researchers have used non-fused cores as the D segment to construct electron acceptors, such as by using electron-rich phenyl, [25][26][27][28][29] thienyl, [30][31][32][33] benzodithiophene, 34,35 etc., and electron-withdrawing benzothiadiazole, 2,[36][37][38] thienopyrroledione, 39,40 benzotriazole, 26 quinoxaline, 41 etc. In order to prevent strong aggregation, steric hindrance via branched side chains or large aromatic side units is usually introduced into the backbones.…”

“…As an alternative, researchers have used non-fused cores as the D segment to construct electron acceptors, such as by using electron-rich phenyl, 25–29 thienyl, 30–33 benzodithiophene, 34,35 etc. , and electron-withdrawing benzothiadiazole, 2,36–38 thienopyrroledione, 39,40 benzotriazole, 26 quinoxaline, 41 etc. In order to prevent strong aggregation, steric hindrance via branched side chains or large aromatic side units is usually introduced into the backbones.…”