## 1 Introduction  
Society needs green and cost-effective technologies for the energy sector owing to the global greenhouse effect and depletion of fossil fuels in recent years. Among all existing green energy technologies such as wind turbines, fuel cells, hydropower, tidal power, solar thermal and biomass, solar cells are considered among the most promising and prominent energy sources [1; 2; 3; 4; 5]. Dye-sensitized solar cells (DSSCs) constitute an advanced generation of solar cells that mimic natural photosynthesis. With fabrication techniques including solution processable methods, the use of cheap materials and decent power conversion efficiency (PCE), DSSSCs are promising candidates for the conversion of solar light into electricity [6; 7; 8]. The highest PCE of 13% has been achieved in DSSSCs by employing ruthenium as a light-absorbing material [9]. Techniques employed to improve the performance of DSSCs aim to minimize recombination of the photoinduced electron hole pair while improving the charge transfer rate of photo-generated electrons in the transparent conducting substrate [10]. Reducing the charge recombination and enhancing charge transfer can be achieved by optimizing the band gap of the semiconducting metal oxide (MOS). The MOS in a DSSC serves as a substrate for dye uplifting as well as provides a path for photoinduced charge generation [11; 12]. TiO\({}_{2}\) nanostructures are one of the significant photoanode materials owing to their superior properties, including wide band gap, large surface area, non-toxicity, low cost and high stability [13; 14]. The morphology of MOS plays a significant role in DSSCs; therefore, a fine-tuned morphology is required to deliver improved PCE in the device [15]. The photocatalytic efficiency of TiO\({}_{2}\) is affected by its ability to respond to radiation (UV along with visible light), and thus could be improved by shifting its optical absorption from UV to the visible region. It has been observed that the photocatalytic efficiency of TiO\({}_{2}\) is enhanced by modifying its band gap with different dopants [16]. A variety of TiO\({}_{2}\) nano-compositions involving nanoparticles, carbon spheres, TiO\({}_{2}\) nanoparticle composites, TiO\({}_{2}\) micro tablets, hollow spheres, nanotube composites, and nano-fiber nanoparticle composites have been successfully synthesized and used as DSSC photoanode materials [17; 18; 19; 20]. Doping with transition metals [21; 22], rare-earth elements [23; 24] and noble metals [25] into TiO\({}_{2}\) has been widely investigated to reduce TiO\({}_{2}\) particle size and improve its (photo)(electro)catalytic performance. Co-doping along with different doping agents including metal-nonmetal, nonmetal-nonmetal, and metal--metal synergistically improves the optical absorption towards the visible region and reduces the recombination process [26]. Cu-N, B-N, Fe-C, Fe-N, Ni-N, and V-N have been studied as co-dopants with TiO\({}_{2}\)[27; 28; 29; 30; 31; 32; 33]. Co-doping of TiO\({}_{2}\) with N-C has been reported to modify its band gap, enhancing its photocatalytic activity towards the visible spectrum [34]. Co-doping of titania nanowires with tungsten carbon improves their electrochemical activity towards the oxygen-evolution reaction (OER) [35]. Ag/V-TiO\({}_{2}\) was also studied to photo-catalyze the degradation of rhodamine B dye in aqueous solutions. These co-doped materials exhibited the highest photocatalytic activity in the UV-visible region [36], Similarly, it has also been previously reported that barium doping in TiO\({}_{2}\) nanoparticles using microwave irradiation increases the optical band gap and reduces the particle size of TiO\({}_{2}\) nanoparticles for microbiological activity [37]. Several studies have reported co-doping of TiO\({}_{2}\) to enhance its optoelectrical properties. The present work deals with the preparation of TiO\({}_{2}\) and Ba/TiO\({}_{2}\) composites using a simple microwave irradiation method.