The surface roughness of the c-TiO2 layer help controls the perovskite grain size without any other parameter. The direct effect of perovskite grain size on PSC performance is clarified.

No abstract

The density functional-based tight binding (DFTB) method has seen a rise in adoption for materials modeling, as it offers significant improvement in scalability with accuracy comparable to the density functional theory (DFT) when good parameterizations exist. The cost reduction in DFTB compared to DFT is achieved by the pre-parameterization of the elements of the Hamiltonian matrix as well as the repulsion potential between all pairs of atoms. Parameterization for new systems with accuracies competitive with DFT in specific applications requires specialized manpower and computational resources. This prevents the application of the DFTB method to systems for which it was not parameterized. In this work, we explore an approach to address the problem of missing parameters of DFTB by modeling the interactions with missing Slater–Koster parameters with an interatomic interaction potential. When the distance between two atoms modeled at the force-field level is sufficiently large, the approach results in accurate structural and electronic properties. The resulting calculation is therefore a hybrid between DFTB and molecular mechanics, a pure DFTB for atoms with a complete set of interatomic parameterizations, and a mix between DFTB and molecular mechanics for atoms with a missing interatomic parameterization. The approach is expected to be particularly useful for hybrid materials and interfaces. The method is tested on the examples of 2D materials, mixed oxides, and a large-scale calculation of an oxide–oxide interface.

An open-chain carboxylic acid host with a chiral sulfinyl group (4) was synthesized from 3,3′-thiobis[(5-tert-butyl-2-hydroxyphenyl)acetic acid] (2) by oxidation of the epithio linkage with mCPBA, followed by acid-catalyzed monoesterification with propan-1-ol. The monoester was resolved via diastereomeric salt formation using quinidine as a resolving agent. The absolute configuration of (+)-4 was assigned to be (R) by X-ray analysis.

A monolithic perovskite/c-Si tandem solar cell has attracted a lot of attention in the field of photovoltaic for its high theoretical energy conversion efficiency and cost-effectiveness. For this technology to reach its potential, optimization and compromised for both perovskite top cell and silicon bottom cell has to be investigated. In a single-junction perovskite solar cell, the hybrid organic-inorganic perovskite light-absorbing layer is sandwiched with electron and hole transporting layers (ETL and HTL). For optimal carrier extraction, the bandgap of the transporting layers has to match the perovskite material such that electron can be selectively transported to the ETL while only hole moves through HTL. In the majority of perovskite solar cells, titanium dioxide (TiO2) is used as ETL, for its high bandgap alignment, ease of fabrication, and low cost. For this reason, a tandem solar cell with c-Si/ETL(TiO2)/Perovskite/HTL structure has the potential to be highly efficient and low in cost [1]. In a single-junction c-Si solar cell, surface passivation of silicon using large bandgap materials such as Al2O3, SiO2 or SiNx is widely known to reduce the velocity of carrier recombination and thus increase the carrier lifetime at silicon surface. This approach, however, is not applicable in tandem solar cells with c-Si/ETL/Perovskite/HTL structure, as the utilization of large bandgap materials in between c-Si and ETL causes bandgap misalignment and prevents interlayer exchange of carriers between perovskite and silicon cells. For this reason, a new approach that accommodates both interlayer exchange of carriers and passivate silicon surface effectively is required. In most of Si-Oxides (Al2O3, TiO2, ZnO, etc.) interface, the existence of SiOx layer is unavoidable and widely known due to high reactivity of silicon surface under oxidizing atmosphere [2]. Furthermore, while the improvement of perovskite solar cell efficiency by controlling spray pyrolysis of TiO2 and the thermal annealing procedure has been reported [3], prolonged exposure to heat during TiO2 fabrication might negatively affect the performance of silicon bottom cell, and thus requires further studies. Due to the high surface passivation effect of thermally grown SiO2 layer, we hypothesized that a proper crystallization of SiOx layer might be able to increase the lifetime of carrier at Si/TiO2 interface and mitigate the surface passivation problem in tandem solar cells with c-Si/ETL/Perovskite/HTL structure. Zone Heating Recrystallization (ZHR) is a process developed by our research group in which the surface of samples was selectively heated by the scanning of highly focus line lamp heater with elliptical mirror. Previously, we reported the utilization of ZHR to obtain smooth seed layers for thin-film silicon solar cell applications [4, 5] among other functionalities. The use of high-intensity lamp heater in ZHR process combines with high transparency of TiO2 layer makes ZHR a suitable process to selectively treat the Si/TiO2 interface and test our hypothesis on SiOx crystallization. With the introduction of ZHR, the minority carrier lifetime of Si/TiO2 interface was increased from less than 5 µs to more than 250 µs. Different scanning rates of lamp heater in ZHR process lead to different carrier lifetime, with higher scanning rates lead to higher carrier lifetime. To explain this phenomenon, cross-sectional TEM images of Si/TiO2 treated with different scanning rate was taken and analyzed. Here, we found that samples treated with higher scanning rates of ZHR have thinner SiOx layer and higher carrier lifetime. The relationship between SiOx thickness and carrier lifetime might be explained with the interface trap density of SiOx layer in which thinner layer shows lower interface trap density. This leads to lower carrier recombination velocity and therefore higher carrier lifetime at Si/TiO2 interface. References Mailoa J. P. et al., A 2-terminal perovskite/silicon multijunction solar cell enabled by a silicon tunnel junction. Appl. Phys. Lett. 106, 121105 (2015). Black L. E. et al., Explorative studies of novel silicon surface passivation materials: Considerations and lessons learned. Solar Energy Materials and Solar Cells 188, 182- 189 (2018). Nukunudompanich M., Ihara M. et al., Dominant effect of the grain size of the MAPbI3 perovskite controlled by the surface roughness of TiO2 on the performance of perovskite solar cell. CrysEngComm 22, 2718-2727 (2020). Ihara M. et al., Fabrication of silicon thin films with defects below detection limit of electron spin resonance for solar cells by high-speed zone-melting crystallization of amorphous silicon. Appl. Phys. Lett. 79, 3809 (2001). Lukianov A., Ihara M. et al., Formation of the seed layers for layer-transfer process silicon solar cells by zone-heating recrystallization of porous silicon structures. Appl. Phys. Lett. 108, 213904 (2016). Figure 1