RESUMEN
Tin halide perovskites are rising as promising materials for lead-free perovskite solar cells (PSCs). However, the crystallization rate of tin halide perovskites is much faster than the lead-based analogs, leading to more rampant trap states and lower efficiency. Here, we disclose a key finding to modulate the crystallization kinetics of FASnI3 through a non-classical nucleation mechanism based on pre-nucleation clusters (PNCs). By introducing piperazine dihydriodide to tune the colloidal chemistry of the FASnI3 perovskite precursor solution, stable clusters could be readily formed in the solution before nucleation. These pre-nucleation clusters act as intermediate phase and thus can reduce the energy barrier for the perovskite nucleation, resulting in a high-quality perovskite film with lower defect density. This PNCs-based method has led to a conspicuous photovoltaic performance improvement for FASnI3 -based PSCs, delivering an impressive efficiency of 11.39 % plus improved stability.
RESUMEN
Technical problems connected with use of the Born-Oppenheimer clamped-nuclei approximation to generate electronic wave functions, potential energy surfaces (PES), and associated properties are discussed. A computational procedure for adjusting the phases of the wave functions, as well as their order when potential crossings occur, is presented which is based on the calculation of overlaps between sets of molecular orbitals and configuration interaction eigenfunctions obtained at neighboring nuclear conformations. This approach has significant advantages for theoretical treatments describing atomic collisions and photo-dissociation processes by means of ab initio PES, electronic transition moments, and nonadiabatic radial and rotational coupling matrix elements. It ensures that the electronic wave functions are continuous over the entire range of nuclear conformations considered, thereby greatly simplifying the process of obtaining the above quantities from the results of single-point Born-Oppenheimer calculations. The overlap results are also used to define a diabatic transformation of the wave functions obtained for conical intersections that greatly simplifies the computation of off-diagonal matrix elements by eliminating the need for complex phase factors.
RESUMEN
An ab initio multireference single- and double-excitation configuration interaction (CI) study is carried out for the ground and excited electronic states of alkali-hydride cations (LiH(+), NaH(+), KH(+), RbH(+), and CsH(+)). For all alkali-metal atoms, the first inner-shell and valence electrons (nine active electrons, three for Li) are considered explicitly in the ab initio self-consistent-field and CI calculations. The adiabatic potential energy curves, radial and rotational couplings are calculated and presented. Short-range (â¼3 a.u.) potential wells produced by the excitation of the inner-shell electrons are found. The depths of the inner potential wells are much greater than those of the outer wells for the CsH(+) system. The computed spectroscopic constants for the long-range potential well of the 2 (2)Σ(+) state are very close to the available theoretical and experimental data. The electronic states of alkali-hydrogen cations are also compared with each other, it is found that the positions of the potential wells shift to larger internuclear distances gradually, and the depths of these potential wells become greater with increasing alkali-metal atomic number. The relationships between structures of the radial coupling matrix elements and the avoiding crossings of the potential curves are analyzed. From NaH(+) to CsH(+), radial coupling matrix elements display more and more complex structures due to the gradual decrease of energy separations for avoided crossings. Finally, the behavior of some rotational couplings is also shown.