# Laser Sintering of TiO\({}_{2}\) Films for Flexible Dye-Sensitized Solar Cells
## 1 Introduction  
Dye-sensitized solar cells (DSCs) have become one of the substitutes for traditional silicon solar cells owing to the simple fabrication process and low fabrication cost [1; 2; 3]. The highest efficiency of DSC has reached \(\sim\)13% [4; 5], almost catching up with that of amorphous Si solar cells [6]. Moreover, DSCs can be fabricated on flexible substrates as a flexible solar cell [7; 8], which has the advantages of easy transportation and roll-to-roll production [9; 10]. However, the incident photon-to-electron conversion efficiency (IPCE) of flexible DSCs has been relatively low. For conventional DSCs prepared on conductive glass substrates, the heart is a several micrometer mesoporous TiO\({}_{2}\) layer, which needs to be annealed at 450-500 \({}^{\circ}\)C to remove the organic additive and achieve electrical connections between the nanoparticles [11; 12]. The widely used indium tin oxide (ITO)-PET or ITO-PEN plastic substrates can only endure thermal treatment below 120 \({}^{\circ}\)C or 150 \({}^{\circ}\)C, which precludes any high-temperature sintering processes and the use of organic binders. Until now, much efforts has been made to improve the inter-nanoparticle physical/electrical contacts of flexible DSCs with a low temperature, including compression [13; 14; 15], lift-off technique [16], ultraviolet (UV) irradiation [17; 18], and chemical sintering [19; 20]. However, a highly efficient and large-area fabrication technique for industrial production still remains a great challenge. Recently, numerous studies on laser processing of TiO\({}_{2}\) films have been conducted [21; 22; 23]. For example, a laserassisted nano-particle deposition system was applied to successfully form sintered TiO\({}_{2}\) films on flexible substrates [24]. The deposition process with a feed rate of 0.025 mm/s is time-consuming, and the corresponding efficiency is only 1.92%. Meanwhile, UV and near-infrared fiber lasers were both used to generate mesoporous nano-crystalline TiO\({}_{2}\) films on ITO or fluorine-doped tin oxide (FTO) coated glasses with a sintering process [25; 26; 27; 28]. However, the conductive glass substrates can withstand a much higher temperature than polyethylene nanphthalate (PEN) and polyethylene terephthalalate (PET) substrates, so the corresponding laser sintering technologies are not suitable for flexible DSCs. [PERSON] et al. fabricated a flexible DSC via membrane transferring and laser sintering [29], and an efficiency of 4.65% could be achieved. Nevertheless, the TiO\({}_{2}\) nanotube membrane fabricated by a potentiostatic anodization method still needs to be annealed at 450 \({}^{\circ}\)C [30], and the detachment process of TiO\({}_{2}\) nanotube arrays is not suitable for industrial production. To simply sinter the TiO\({}_{2}\) nanoparticles films on plastic substrates, [PERSON] et al. proposed to use selective laser sintering to improve the efficient of flexible DSCs [31], with a sintering efficiency of 0.02 m\({}^{2}\)/h, an ICPE of 5.6% could be achieved. Even so, the sintering efficiency struggles to meet the requirement of industrial production, and the corresponding improvement approach was not proposed. Besides, the key laser parameters determining the sintering effect were not systematically investigated, and the potential laser sintering mechanism was not demonstrated. These contents are of great significance for large-scale industrial production. Laser sintering efficiency is very important for industrial manufacture, and the influence of sintering parameters on the photoelectric performance of flexible DSCs is of great significance to design the laser sintering system and improve the sintering efficiency. In this paper, to improve the IPCE of flexible DSCs, we reported a simple approach to sinter TiO\({}_{2}\) nanoparticle electrodes using a laser processing technique, which is a method of easy operation and fast fracture as well as industrialization continuous production.