Computational Verification of So-Called Perovskite Solar Cells as PbI64−-Aligned Solar Cells

Abstract

Effective sensitizing components in so-called perovskite solar cells (PSC) are lead hexaiodide (PbI64−) salts of PbI64− (MeNH3+)n (n = 2∼4). Density-functional-theory-based molecular modeling (DFT/MM) of X-ray crystalline structure of PbI64−/MeNH3+ salt (FOLLIB) verifies that the packing unit of FOLLIB has UV/Vis absorption spectrum at λmax = 424 nm, giving pale yellow color as complementary color. DFT/MM of the horizontal component in the FOLLIB gives narrow energy gap of 0.3 eV, verifying remarkable semiconducting property through tight alignments of PbI64− components coupled with MeNH3+. DFT/MM of the central PbI64−/MeNH3+ components verifies that the central component has UV/Vis absorption spectra with respective λmax = 570 nm, λmax = 762 nm and λmax = 945 nm, and plays an essential role as panchromatic sensitizers. In addition, their equilibrium geometric structures show slightly hypsochromic UV/Vis absorption spectra at respective λmax = 486 nm, λmax = 560 nm, and λmax = 563 nm as results of migration of MeNH3+ close to PbI64−. DFT/MM also verifies that PbI64− components align tightly to nanocrystalline TiO2 (nc-TiO2) and to spiro-OMeTAD in PSC through electron density induced by van der Waals interaction. Electron density-based alignments of PbI64− components well explain unidirectional and leakage-free electron diffusion leading to high open-circuit voltage in PbI64−-aligned solar cells. At the same time, the semiconducting and panchromatic sensitizing layer of PbI64−/MeNH3+ components contribute to excellent short-circuit photocurrent of PbI64−-aligned solar cells.