ABSTRACT
The simultaneous improvement of efficiency and stability of organic solar cells (OSCs) for commercialization remains a challenging task. Herein, we designed asymmetric acceptors DT-C8Cl and DT-C8BTz with functional haloalkyl chains, in which the halogen atoms could induce noncovalent interactions with heteroatoms like O, S, and Se, etc., thus leading to appropriately manipulated film morphology. Consequently, binary devices based on D18: DT-C8Cl achieved a champion power conversion efficiency (PCE) of 19.40 %. The higher PCE of D18: DT-C8Cl could be attributed to the enhanced π-π stacking, improved charge transport, and reduced recombination losses. In addition, the noncovalent interactions induced by haloalkyl chains could effectively suppress unfavorable morphology evolutions and thereby reduce trap density of states, leading to improved thermal and storage stability. Overall, our findings reveal that the rational design of asymmetric acceptors with functional haloalkyl chains is a novel and powerful strategy for simultaneously enhancing the efficiency and stability of OSCs.
ABSTRACT
It is of vital importance to improve the long-term and photostability of organic photovoltaics, including organic solar cells (OSCs) and organic photodetectors (OPDs), for their ultimate industrialization. Herein, two series of terpolymers featuring with an antioxidant butylated hydroxytoluene (BHT)-terminated side chain, PTzBI-EHp-BTBHTx and N2200-BTBHTx (x = 0.05, 0.1, 0.2), are designed and synthesized. It was found that incorporating appropriate ratio of benzothiadiazole (BT) with BHT side chains on the conjugated backbone would induce negligible effect on the molecular weight, absorption spectra and energy levels of polymers, however, which would obviously enhance the photostability of these polymers. Consequently, all-polymer solar cells (all-PSCs) and photodetectors were fabricated, and the all-PSC based on PTzBI-EHp-BTBHT0.05: N2200 realized an optimal power conversion efficiency (PCE) approaching ~ 10%, outperforming the device based on pristine PTzBI-EHp: N2200. Impressively, the all-PSCs based on BHT-featuring terpolymers displayed alleviated PCEs degradation under continuous irradiation for 300 h due to the improved morphological and photostability of active layers. The OPDs based on BHT-featuring terpolymers achieved a lower dark current at - 0.1 bias, which could be stabilized even after irradiation over 400 h. This study provides a feasible approach to develop terpolymers with antioxidant efficacy for improving the lifetime of OSCs and OPDs.
