ZnO/CdS based high performance broadband photo-chargeable flexible supercapacitor

Photo-chargeable supercapacitors are attracting significant research interest as promising alternative to energy storage devices suitable for next-generation smart appliances. In this work, a heterojunction of cadmium sulphide (CdS) nanoparticles and zinc oxide (ZnO) nanorods is obtained for designing a broadband photo responsive symmetrical supercapacitor. Ultraviolet (UV) absorption by ZnO and visible light interaction with the CdS nanoparticles in the heterostructure contribute synergistically to deliver UV to visible broad spectral response. The heterojunction formation is confirmed by field effect scanning electron microscopy and high-resolution transmission electron microscopy with elemental mapping. Areal capacitance was measured in both the dark and under illumination conditions using cyclic voltammetry and galvanostatic charge-discharge, supported by impedance spectroscopy. Enhancement of areal capacitance from the dark condition was observed between -238% to -1264% for different illumination in broad spectral range measured from the cyclic voltammetry measurements at a constant scan rate of 50 mV s-1 and achieved a highest capacitance value of -139 mu F cm-2 under 475 nm visible light for the scan rate of 10 mV s-1. Moreover, the charge generation and storage mechanism under illumination were verified by phototransient response and open-circuit potential measurements. The excellent electrochemical performance observed by maintaining high efficiency (-94.7%) with improved cyclic stability upto 5000 cycles. A good capacitance retention (-90%) in bending mode when heterojunction applied in bendable devices provide broad future prospect for the metal oxide-sulphide interface in photo-chargeable smart devices.