• Energy Research

Abstract Three small molecule acceptors (SMAs), named ZF, ZC and ZB, have been designed and synthesized for organic solar cells (OSCs) by introducing single F, Cl and Br atom on each terminal unit, respectively. The effects of different halogen substituent on molecular aggregation, photophysical and photovoltaic performance have been systematically studied. Owing to its strong electronegativity of halogens, all the acceptors with monohalogenated terminal units possess red-shifted absorption spectra and deeper frontier energy levels compared to the corresponding acceptor without halogen substituents reported in the literature. Among the SMAs, ZB with brominated terminal units was found to show the higher molar absorption coefficient (2.31 × 105 M−1 cm−1), more orderly face-on π-π stacking, higher electron mobility and more favorable morphology when blended with PM6. As a result, the PM6:ZB OSCs yielded a high power conversion efficiency (PCE) of up to 15.23% with a high short-circuit current density (Jsc) of 26.38 mA cm−2, while the corresponding ZF- and ZC-based devices showed the relatively inferior PCEs of 13.36% and 14.71%, respectively. These results demonstrated that the modulation of electron-withdrawing halogen substituents on terminal group provides a promising strategy to design and synthesize efficient SMAs for fabricating high-performance OSCs.

Abstract Three small molecule acceptors (SMAs), named ZF, ZC and ZB, have been designed and synthesized for organic solar cells (OSCs) by introducing single F, Cl and Br atom on each terminal unit, respectively. The effects of different halogen substituent on molecular aggregation, photophysical and photovoltaic performance have been systematically studied. Owing to its strong electronegativity of halogens, all the acceptors with monohalogenated terminal units possess red-shifted absorption spectra and deeper frontier energy levels compared to the corresponding acceptor without halogen substituents reported in the literature. Among the SMAs, ZB with brominated terminal units was found to show the higher molar absorption coefficient (2.31 × 105 M−1 cm−1), more orderly face-on π-π stacking, higher electron mobility and more favorable morphology when blended with PM6. As a result, the PM6:ZB OSCs yielded a high power conversion efficiency (PCE) of up to 15.23% with a high short-circuit current density (Jsc) of 26.38 mA cm−2, while the corresponding ZF- and ZC-based devices showed the relatively inferior PCEs of 13.36% and 14.71%, respectively. These results demonstrated that the modulation of electron-withdrawing halogen substituents on terminal group provides a promising strategy to design and synthesize efficient SMAs for fabricating high-performance OSCs.

Ferrocene was introduced as a solid additive in organic solar cells (OSCs). The use of ferrocene provides PM6:Y6 based device with improved performance and stability, demonstrating its great potential in the fabrication of efficient and stable OSCs.

Ferrocene was introduced as a solid additive in organic solar cells (OSCs). The use of ferrocene provides PM6:Y6 based device with improved performance and stability, demonstrating its great potential in the fabrication of efficient and stable OSCs.

To face the challenge of all-climate application, organic rechargeable batteries must hold the capability of efficiently operating both at high temperatures (>50 °C) and low temperatures (-20 °C). However, the low electronic conductivity and high solubility of organic molecules significantly impede the development in electrochemical energy storage. This issue can be effectively diminished using functionalized porphyrin complex-based organic cathodes by the in-situ electropolymerization of electrodes at elevating temperatures during electrochemical cycling. [5,15-bis(ethynyl)-10,20-diphenylporphinato]copper(II) (CuDEPP)- and 5,15-bis(ethynyl)-10,20-diphenylporphinato (DEPP)-based cathodes are proposed as models, and it is proved that a largely improved electrochemical performance is observed in both cathodes at a high operating temperature. Reversible capacities of 249 and 105 mA h g-1 are obtained for the CuDEPP and DEPP cathodes after 1000 cycles at 50 °C, respectively. The result indicates that the temperature-induced in situ electropolymerization strategy responds to the enhanced electrochemical performance. This study would open new opportunities for developing highly stable organic cathodes for electrochemical energy storage even at high temperatures.

To face the challenge of all-climate application, organic rechargeable batteries must hold the capability of efficiently operating both at high temperatures (>50 °C) and low temperatures (-20 °C). However, the low electronic conductivity and high solubility of organic molecules significantly impede the development in electrochemical energy storage. This issue can be effectively diminished using functionalized porphyrin complex-based organic cathodes by the in-situ electropolymerization of electrodes at elevating temperatures during electrochemical cycling. [5,15-bis(ethynyl)-10,20-diphenylporphinato]copper(II) (CuDEPP)- and 5,15-bis(ethynyl)-10,20-diphenylporphinato (DEPP)-based cathodes are proposed as models, and it is proved that a largely improved electrochemical performance is observed in both cathodes at a high operating temperature. Reversible capacities of 249 and 105 mA h g-1 are obtained for the CuDEPP and DEPP cathodes after 1000 cycles at 50 °C, respectively. The result indicates that the temperature-induced in situ electropolymerization strategy responds to the enhanced electrochemical performance. This study would open new opportunities for developing highly stable organic cathodes for electrochemical energy storage even at high temperatures.

Abstract Two A2-D-A1-D-A2-type small molecule acceptors (SMAs), DFB-dIDT and BT-dIDT with 2,5-difluorobenzene (DFB) or benzothiadiazole (BT) as electron-withdrawing core (A1) and a derivative of indanone as A2 units, were prepared for applications in organic solar cells (OSCs). The results indicate that BT unit is more beneficial to forming multiple noncovalent conformational locks of N⋯S and N⋯H between BT and IDT unit than DFB in the core, so BT-dIDT showed better molecular coplanarity, higher-lying HOMO energy level, more red-shifted spectrum, superior molar absorption coefficient (1.60 × 105 M−1 cm−1 at 696 nm), more complementary absorption spectrum with PBDB-T and better photovoltaic performance than DFB-dIDT. As a result, the BT-dIDT-based OSCs blending with PBDB-T exhibited higher power conversion efficiency (PCE) value of 10.52% with higher Jsc of 18.59 mA cm−2 than that of the DFB-dIDT-based devices (PCE of 6.71% with Jsc of 15.58 mA cm−2). These results demonstrate that the A2-D-A1-D-A2-type SMAs incorporated with a suitable electron-deficient core are promising candidates for high performance OSCs.

Abstract Two A2-D-A1-D-A2-type small molecule acceptors (SMAs), DFB-dIDT and BT-dIDT with 2,5-difluorobenzene (DFB) or benzothiadiazole (BT) as electron-withdrawing core (A1) and a derivative of indanone as A2 units, were prepared for applications in organic solar cells (OSCs). The results indicate that BT unit is more beneficial to forming multiple noncovalent conformational locks of N⋯S and N⋯H between BT and IDT unit than DFB in the core, so BT-dIDT showed better molecular coplanarity, higher-lying HOMO energy level, more red-shifted spectrum, superior molar absorption coefficient (1.60 × 105 M−1 cm−1 at 696 nm), more complementary absorption spectrum with PBDB-T and better photovoltaic performance than DFB-dIDT. As a result, the BT-dIDT-based OSCs blending with PBDB-T exhibited higher power conversion efficiency (PCE) value of 10.52% with higher Jsc of 18.59 mA cm−2 than that of the DFB-dIDT-based devices (PCE of 6.71% with Jsc of 15.58 mA cm−2). These results demonstrate that the A2-D-A1-D-A2-type SMAs incorporated with a suitable electron-deficient core are promising candidates for high performance OSCs.