The important factor for improving the performance of FAPbI3 perovskite solar cells is the crystallinity of the α-phase FAPbI3 perovskite structure. Our theoretical framework can be used to understand other additives, which can affect the crystallinity of the α-phase FAPbI3 perovskite structure and device performance.
Introduction
Introduction of Nanophotonics
- General Introduction of Nanophotonics
- Localized Surface Plasmon Resonance (LSPR) of Metal Nanoparticle
- Upconversion Nanocrystal (UCN)
- Perovskite Nanophotonics
The research field of plasmonics is growing rapidly6 after the theoretical prediction of plasmons in 1956 by David Pines7 (Figure 1.2(b)). a) Schematic of localized surface plasmon resonance (LSPR) of a metal nanoparticle. In general, the thermal stability of the α-phase perovskite structure is low at room temperature and suffers from a spontaneous phase transition from the α-phase to the δ-phase perovskite (non-photoactive structure) (Figure 1.9).37.
Introduction of Computer Simulation
- Importance of Computer Simulation
- Multiscale Computational Approach
Multiscale computational approach according to time and length scales; density functional theory (DFT) calculation, molecular dynamics (MD) simulation, and continuum electrodynamics (CED) simulation. The CED simulation can perform the largest scale simulation (i.e. time: over second and length: over meter) compared to the above methods.
Theoretical Study on LSPR Characteristics of Metal Nanoparticle for Sensor and
Study on Enhancement of Sensing Capability of Plasmonic Dimer Structure with Polymer
- Introduction
- Computational Details
- Results and Discussion
- Conclusion
- References
The size of the Au-NP and the thickness of the polymer shell are extracted from the maximum size (diameter = 7.6 nm) of the self-assembled Au-NP in the DPD simulation. The variations of electric field intensity for each model system from Figure 2.1.4 with respect to the radial distance from the center of the Au-NP. Equations for the underlying Au-NP surface (red dashed line) and the polymer shell surface (blue dashed line) in terms of polymer shell thickness (t) were estimated by fitting the values of the electric field, respectively.
Absorption cross section of monomer in dimer (Cabs/2) with respect to gap distance. To investigate the detection accuracy of the dimer model system, the FWHM values were evaluated from the gap distance of 0 nm to 9 nm. On the other hand, the maximum sensitivity was significantly decreased at the distance of 0.2 nm by reducing the electric field intensity of the main peak, and the sensitivity was further decreased by the effect of electron tunneling (Figure 2.1.11 (a)).
Importantly, the electric field intensity of the secondary peak (BDP mode) at 0.2 nm spacing was ~33% greater than that of the main peak (BDP mode) at 0.4 nm spacing, even under electron tunnel effect (Figure 2.1. 11(b)).
Effect of Surrounding Environment on LSPR Intensity of Ag Quantum Dot for Improving
- Introduction
- Computational Details
- Results and Discussion
- Conclusion
- References
Theoretical Study on Luminescence Characteristics of UCN for Understanding
- Introduction
- Computational Details
- Results and Discussion
- Conclusion
- References
Note that for the hexagonal apatite phase, all possible configurations where Na+ and Y3+ ions were placed in the 6h Wyckoff positions were investigated and the most stable configuration was adopted. Note that although the imaginary frequency (negative frequency), indicating structural instability, appeared in the cubic and hexagonal apatite phases, the contribution to the instability of the entire structure was very marginal because the intensity was very weak.
Theoretical Study on Crystallinity of α-Phase Perovskite Structure for High
Introduction
Organic-inorganic lead halide perovskite structure (ABX3) is widely used in the research field of solar cells with high power conversion efficiencies (> 25%).1 The high efficiency of the unit performance of perovskite solar cells is caused by their exceptional material properties, 2-4 which have a high optical absorption cross section, 5 low binding energy of exciton, 6 long-range diffusion length of charge carrier, 3,7,8 and tunable band gap 8-10 through the change of the precursor. In general, although FAPbI3 has two crystal phase structures, which are a non-perovskite δ-phase (yellow phase) and a 3D perovskite α-phase (black phase), only α-phase perovskite can be used as a photoactive phase.12,14 However black α-phase perovskite is easily converted to the yellow δ-phase non-perovskite at room temperature due to the large size of the FA cation.15 Therefore, the studies have shown that substituting some of the FA+ cations with MA+ or Cs+ can inhibit this phase transformation.12. The important factors to achieve high-performance perovskite solar cells are to control the well-defined morphologies and maintain the high crystallization of the perovskite film.16,17 These factors can be controlled by the perovskite precursor,18 fabrication method,19 solvent mixture,17 annealing conditions,20,21 fabrication humidity conditions, 22 surface passivation,23 and processing additives.24 In recent years, the incorporation of additives into the perovskite precursor solution has been widely investigated to provide an effective method which improves the morphology and crystallinity of perovskite films.
Therefore, the addition of cationic iodide to a precursor solution has been widely studied in efforts to achieve high-performance perovskite solar cells. In this study, we systematically investigated the role of MACl additive in terms of formation energy, electronic properties (orbital and density of states) and volume shrinkage using density functional theory (DFT) calculation. Our study indicates that MACl addition is a promising material for improving the crystallinity of perovskite film and the device performance, which provides great opportunities for the practical applications.
Top) Scanning electron microscope (SEM) images of α-phase FAPbI3 perovskite structure with/without MACl additive.
Computational Details
Results and Discussion
Model systems of the α-phase FAPbI3 perovskite structure and Cl or MACl additive-incorporated α-phase FAPbI3 perovskite structures. Note that the formation energy (ΔEf) of the α-phase FAPbI3 perovskite structure prepared with chloride, cation, or cation chloride was calculated using the following equation. Highest occupied molecular orbitals (HOMOs) of bare α-phase FAPbI3 perovskite structure and that with Cl, MA or MACl.
Total volume and cubo-octahedral structure of bare FAPbI3 perovskite structure in α phase and that prepared with MA. Finally, in the experimental results, the crystallinity of the FAPbI3 perovskite structure in the α phase was changed according to the concentration of MACl (Figure 4.10). In the pre-annealing step of the FAPbI3 α-phase perovskite structure, the doping formation energy of the cationic chloride additive in the perovskite structure (ΔEd) was calculated using the following equation.
Note that model systems of α-phase FAPbI3 perovskite structure including (a) MACl or (b) MAI are described according to their concentration from 11% to 44%.
Conclusion
The optimal concentration of MACl additive was caused by the dopant formation energy of MACl in the a-phase FAPbI3 perovskite structure in the pre-annealing step and the formation energy of the perovskite structure including MAI in the post-annealing step. In particular, the formation energy was stabilized between 33% and 44%, which corresponded to the best performance shown in the experiment (i.e., 40%). Generally, we can understand the role of MACl additive in the formation of perovskite structure through three points of DFT calculation.
W.; Yan, F., Efficient and stable perovskite solar cells prepared in ambient air regardless of humidity. Li, T.; Pan, Y.; Wang, Z.; Xia, Y.; Chen, Y.; Huang, W., Dopant engineering for high efficiency organic-inorganic halide perovskite solar cells: Recent progress and perspectives. Zhao, Y.; Zhu, K., Efficient Planar Perovskite Solar Cells Based on 1.8 eV Band Gap CH3NH3PbI2Br Nanosheets via Thermal Decomposition, J.
Chu, C.-W., Synergistic improvements in stability and performance of lead iodide perovskite solar cells incorporating salt additives. Chen, Y.; Zhao, Y.; Liang, Z., Non-Thermal Annealing Fabrication of Efficient Planar Perovskite Solar Cells with inclusion of NH4Cl. Qin, C.; Matsushima, T.; Fujihara, T.; Adachi, C., Multifunctional benzoquinone additive for efficient and stable planar perovskite solar cells.
P.; Cui, G., Additive-modulated development of HC(NH2)2PbI3 black polymorph for mesoscopic perovskite solar cells.
Summary and Future Perspectives
Summary
The MACl additive improved the thermodynamic stability of the α-phase FAPbI3 perovskite structure due to the localization and strengthening of p-orbital I, which resulted in improving the interaction between FA and I in the cubo-octahedral site of the perovskite structure . Moreover, the volume shrinkage in the perovskite structure with MA cations improved the stability of the perovskite structure by improving the interaction between FA and I. Finally, we theoretically elucidated the effect of MACl concentration on the crystallinity of the perovskite structure in terms of the doping formation energy. of MACl in the perovskite structure and the formation energy of the perovskite structure with MA cations.
In conclusion, we investigated the characteristics of various nanomaterials (i.e., metallic nanoparticles, rare-earth doped nanocrystals, and organic-inorganic perovskite) for their application in nanophotonics using a multiscale computational approach. We expect that our theoretical frameworks, established in the above four chapters, can be used to effectively understand the characteristics of nanomaterials and to develop the novel nanomaterials for nanophotonics applications.
Future Perspectives
Third, although the perovskite solar cells have received intensive attention due to their high energy conversion efficiency, low cost and simple fabrication process, the improvement of the crystallinity and stability of the perovskite structure should be addressed for the purpose of its commercialization. Experimentally, many efforts have been made to discover and develop the perovskite structure of a new ABX3. A recent study reported that doping with doubly charged methylene diammonium (MDA2+) in a perovskite site showed superior thermal and humidity stability with high conversion efficiency (i.e. indicating that more atomic screening may be possible due to the expansion of charge states from A, B and X locations.
To accelerate these types of computational analysis, we need to combine it with machine learning techniques, which have received a lot of attention recently. We anticipate that the combination of our theoretical frameworks in Chapter 4 and machine learning technique will show a synergistic effect in the new perovskite structure design with high crystallinity and stability, ultimately enabling improved device performance. Finally, based on our theoretical frameworks, which were presented in this dissertation, we will computationally design nanomaterials that represent new nanophotonics, such as metamaterials, using multiscale computational techniques combined with machine learning.
We believe that this kind of computational design can save time and cost for experiments and become the target of the research fields of computer simulations.
Dahye Baek†, Tae Kyung Lee†, Inkyu Jeon†, Se Hun Joo, Subeen Shin, Jaehyun Park, Seok Ju Kang*, Sang Kyu Kwak* og Jiseok Lee*. Yoon Ho Lee†, Tae Kyung Lee†, Hongki Kim, Inho Song, Jiwon Lee, Saewon Kang, Hyunhyub Ko, Sang Kyu Kwak* og Joon Hak Oh*. Youngoh Lee†, Jiwon Lee†, Tae Kyung Lee†, Jonghwa Park, Minjung Ha, Sang Kyu Kwak* og Hyunhyub Ko*.
Seyeong Song†, Jungwoo Heo†, Tae Kyung Lee, Soojin Park, Bright Walker, Sang Kyu Kwak* and Jin Young Kim*. Wen Xu, Tae Kyung Lee, Byeong-Seok Moon, Donglei Zhou, Hongwei Song, Young-Jin Kim, Sang Kyu Kwak*, Peng Chen* and Dong-Hwan Kim*. Yoon Ho Lee, Tae Kyung Lee, Inho Song, Hojeong Yu, Jiwon Lee, Hyunhyub Ko, Sang Kyu Kwak* and Joon Hak Oh*.
Anirban Dandapat, Tae Kyung Lee, Ziming Zhang, Sang Kyun Kwak, Eun Chul Choong Dong-Hwan Kim te an ni.
