## 4 Conclusions  
This work successfully obtained the optimum design of 2D nanodisk hexagonal photonic crystals for PSC application using the FDTD method. The radius of photonic crystals has been varied from 37.5-225 nm, and the lattice constant is varied from 450-1125 nm. The results show that the nanodisk PC with 225 nm of radius and 500 nm of lattice constant provides the highest absorption, with up to 94% of the incident light absorbed. It also gives the highest \(J_{sc}\), which is 26.473 mA/cm\({}^{2}\). From this work, it is known that when the radius of nanodisk PC increases, the absorption also increases. This occurs because the larger the PC radius, the more photon from the incident light can be in slow photon mode. On the other hand, when the lattice constant is increased, the absorption is decreased due to larger spacing on the structure so that the photon that moves into slow photon mode is fewer. It is best to keep the spacing of the photonic crystal at a minimum and the surface area of the photonic crystal larger to achieve the photon being in slow photon mode. The application of nanodisk photonic crystals in PSC is proven to enhance the absorption higher than that of the flat PSC. This study proved that the PC is advantageous for optimizing solar cell performance. Further study will simulate the electrical properties of the proposed design as a preliminary study for the actual application of solar cells.  
Figure 5: Electromagnetic field density profile of flat and PC-based PSC in 390 nm, 642 nm, 759 nm, and 900 nm.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Structure** & **PC Shape** & **Absorption** & \(J_{sc}\) **(mA/cm\({}^{2}\))** & **Reference** \\ \hline FTO/TiO\({}_{2}\)/MAPbI\({}_{3-x}\)Cl\({}_{x}\)/Spiro-OmeTAD & Inverse Opal & 55\% & 17.1 & [40] \\ \hline FTO/TiO\({}_{2}\)/MAPbI\({}_{3}\)/Spiro-OmeTAD & Nanorod & 57\% & 19.18 & [41] \\ \hline FTO/TiO\({}_{2}\)/MAPbI\({}_{3}\)/Spiro-OmeTAD & Inverse Opal & 72\% & 14.9 & [42] \\ \hline FTO/TiO\({}_{2}\)/MAPbI\({}_{3}\)/Spiro-OmeTAD & Hemisphere & 82\% & 26.5 & [22] \\ \hline FTO/TiO\({}_{2}\)/MAPbI\({}_{3}\)/Spiro-OmeTAD & Nanodisk & 87\% & 26.5 & This work \\ \hline \hline \end{tabular}
\end{table}
Table 3: The comparison of optical performance in this work with previous studies about application of PC on PSC at 446 nm of wavelength.  
**Author Contributions:** [PERSON], A.A., provided the conceptualization, original draft, investigation, and formal analysis; [PERSON] provided methodology, data curation, and investigation; [PERSON] and [PERSON] provided validation, article review and editing; [PERSON] provided validation and software; [PERSON] provided validation provided funding acquisition and supervised the project. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was supported by funding from the Ministry of Education, Culture, Research, and Technology, Republic of Indonesia with grant 276/UN40.LP/PT.01.03/2021 and World Class University Program from Universitats Pendidikan Indonesia.  
**Acknowledgments:** The authors thank Universitats Pendidikan Indonesia for providing the facility and supports for conducting progress meetings. Also, the Institute of Microengineering and Nanoelectronics (IMEN), Universiti Kebangsaan Malaysia for giving access to the license of Lumerical software.  
**Conflicts of Interest:** The authors declare that there are no conflict of interest regarding the publication of this paper.