Insight into the development and behaviour of (TiO2)0.9 + ((ZnO/ZnS):x% rGO)0.1 composites as photoelectrodes in DSSCs

Abstract

Development of photoelectrodes for solar cells offers a strategy to achieve more efficient photon conversion systems. This work develops (TiO₂)_0.9 + ((ZnO/ZnS):x% rGO)_0.1 photoelectrodes with rGO contents of 0.5, 1 and 2%, investigating the influence of the ZnO/ZnS–rGO heterostructure on their structural, electronic, optical, and photovoltaic behavior. The ZnO/ZnS composite was synthesized using the microwave-assisted hydrothermal (MAH) method, and the dye-sensitized solar cell (DSSC) films were deposited by spin-coating. All samples were successfully synthesized, reporting the heterostructure of hexagonal (ZnO) and cubic (ZnS). The sample containing the lowest amount of rGO (0.5%) exhibited the best photovoltaic performance, with an increase in short-circuit current density (J_sc) compared to the TiO₂ DSSC. This morphological improvement resulted in a notable enhancement of device performance, with efficiency increasing by approximately 62.5%. The increase in the efficiency of photovoltaic devices was attributed to the improvement achieved in band alignment as a result of the hybridization structure. This development reduces recombination processes and promotes charge transfer, as demonstrated by electrochemical impedance measurements. The spatial separation between electrons and holes in the ZnO/ZnS structure, combined with the role of reduced graphene oxide (rGO) as an efficient electron acceptor, contributes to these improvements.