With the rapid depletion of global fossil resources and the acceleration of urbanization, the development of clean and sustainable energy has become imperative. Among various alternative energy sources, solar energy stands out for its cleanliness and abundance, with solar cells being the primary means of utilizing this resource. Dye-sensitized solar cells (DSSCs) are a highly promising third-generation photovoltaic technology, featuring low cost, convenient manufacturing, and abundant materials. However, traditional DSSCs based on liquid electrolytes have problems such as leakage and poor long-term stability. Solid-state DSSCs (ssDSSCs) effectively address these shortcomings, offering higher durability and operational stability. Despite these advantages, ssDSSCs still face key challenges, including insufficient light collection efficiency and rapid charge recombination. In recent years, D-A-π-A structured dyes have attracted great interest due to their ability to enhance intramolecular spatial resistance by introducing long alkoxy chains as donor substituents. This structural modification can effectively suppress charge recombination and improve the performance of the device. In this study, D-A-π-A-based dyes are used as the sensitizing agent layer in the modeling of ssDSSCs. The purpose is to systematically study its influence on the device performance through simulation. We aim to provide theoretical guidance for optimizing ssDSSC performance, thereby promoting their large-scale application and industrial development.

Based on the SCAPS-1D simulation software, we construct a solid-state dye-sensitized solar cell model with the FTO/TiO₂/AQ310/Spiro-OMeTAD/Ag structure. The photoelectric performance is systematically optimized by the control variable method. By analyzing key photoelectric parameters such as open-circuit voltage (V_oc), short-circuit current density (J_sc), fill factor (FF), and photoelectric conversion efficiency (PCE), the influence of various factors on device performance is evaluated. Furthermore, the two-factor dynamic variational method is adopted to deeply study the influence of the synergistic changes in the defect density and thickness of the dye layer, the doping concentration of both the electron transport layer (ETL) and the hole transport layer (HTL) on battery performance. Meanwhile, the regulatory effects of environmental temperature and the selection of back electrode materials on device performance are explored. Based on the analysis of the optimization results for each parameter, the mechanism of its effect on the performance of the DSSC is revealed, which provides a reference basis for the theoretical simulation and practical design of solid-state DSSCs.

When the thickness of the dye layer is relatively small, appropriately increasing its defect density is helpful to enhance the performance of the device. However, when the thickness exceeds 700 nm, the improvement of the photoelectric parameters tends to be slow, the light absorption gradually approaches saturation, and at the same time, the carrier transport path becomes longer and the recombination effect intensifies, which limits the further improvement of performance (Fig. 3). When the thickness of the dye layer is fixed at 700 nm, the device performance is better at a low defect density. However, as the defect density increases, the carrier recombination effect intensifies, which results in a decline in performance. When the defect density is 10¹⁵ cm^-3, the device exhibits the best photoelectric performance (Fig. 4). It is found in the doping concentration analysis that the influence of HTL doping concentration on V_oc is relatively weak, while the change of ETL doping concentration has a significant enhancing effect on V_oc. When the doping concentration of HTL is fixed, V_oc continuously increases with the increase of the doping concentration of ETL. In contrast, J_sc is not sensitive to changes in the doping concentration of ETL. However, FF is significantly affected by the ETL doping concentration. Under high doping conditions, the carrier mobility increases and the interface recombination loss decreases, thereby significantly enhancing FF (Fig. 5). In addition, the increase in doping concentration will also lead to a decrease in the width of the depletion region, shorten the carrier transport path, and reduce the recombination probability, thereby further enhancing J_sc and FF (Fig. 6). Temperature also has a significant effect on the performance of devices. As the temperature rises, the band gap of the material gradually narrates, thus resulting in a decrease in V_oc, while at the same time, J_sc increases. In the short-wavelength range, the increase in temperature enhances the electron mobility and reduces the interfacial potential barrier, resulting in a significant improvement in quantum efficiency (QE). In the long-wavelength region, the collection efficiency of photogenerated carriers remains stable, and QE curves basically overlap (Fig. 7). The variation of the work function of the back contact metal also has an important influence on the performance of the device. With the increase of the work function, the energy level matching between HTL and the metal back electrode improves, and J-V characteristics and PCE of the device are significantly enhanced. When the work function is further increased, the barrier height of the majority of carriers significantly decreases, forming ohmic contacts. These device parameters tend to be saturated, and the performance no longer improves significantly. Comprehensively considering performance, cost and resource availability, carbon (C) as the back contact metal is a more suitable choice.

We use the D-A-π-A dye AQ310 as the photosensitive material, and construct the FTO/TiO₂/AQ310/Spiro-OMeTAD/Ag device structure based on the SCAPS-1D software. In addition, we systematically study these effects of key factors such as the thickness of the dye layer, defect density, doping concentrations of ETL and HTL, working temperature, and back contact metal on the performance of solid-state DSSC. These results show that, on the premise of a low defect density in the dye layer, appropriately increasing the thickness is helpful in improving the performance of the device. Higher doping concentrations of ETL and HTL can significantly improve the photoelectric parameters. Although the increase in temperature can enhance the short-circuit current, the narrowing of the material band gap leads to a decrease in the open-circuit voltage, and the overall efficiency is somewhat reduced. Improving the work function of the back contact metal optimizes the characteristics of the HTL/ metal interface. Among them, carbon materials show good application prospects due to their performance, cost and resource advantages. Based on an in-depth analysis of various influencing factors, we systematically optimize the device parameters and finally achieve excellent performance with V_oc=0.950 V, J_sc=19.84 mA·cm^-2, FF of 79.80%, and PCE of 15.05%. It provides theoretical support for the structural design and performance improvement of solid-state DSSC. This study not only helps promote the development of solid-state DSSC towards commercialization but also provides a feasible path for its application in fields such as large-scale photovoltaic system integration and green energy utilization. It is worth noting that compared with the theoretical efficiency limit, there is still considerable room for improvement in the device performance. In the future, strategies such as optimizing the molecular structure of dyes to expand the absorption range and introducing an interface passivation layer to reduce recombination losses can be adopted to further enhance the performance and stability of the devices.