Shozo Yanagida
Professor
Title: Computational verification of so-called perovskite solar cells using density functional theory
Biography
Biography: Shozo Yanagida
Abstract
So-called perovskite solar cells (PSC) are composed of PbI64- (MeNH3+)4 salt, where PbI64- plays an essential role as an effective solar light sensitizer with keeping semiconducting property even when aligned each other. Density-functional-theory-based molecular modeling (DFT/MM) using reported X-ray crystallographic structure of PbI64-/MeNH3+/H2O salt (named FOLLIB in Cambridge Structural Data) validates that the packing unit consisting of {(PbI64-)9[(MeNH3+)2-H2O]2(MeNH3+-H2O)2(MeNH3+)2}28- should show UV/Vis absorption spectrum at lmax=424 nm (pale yellow color) as observed for the PbI64- crystal. DFT/MM of the FOLLIB horizontal aligned component, [(PbI6 4-[(MeNH3+)2-H2O]2(MeNH3+-H2O)2(MeNH3+)2/(PbI6 4-)2)4- verifies that the component has narrow energy gap of 0.3eV, predicting excellent semiconducting property of the PbI64- alignment with MeNH3+. Three H2O-free PbI64-/MeNH3+ aligned components, PbI64-(MeNH3+)4, [PbI64-(CH3NH3+)3]- and [PbI64-(CH3NH3+)2]2- are molecular modeled and verified to have UV/Vis spectra at lmax=570nm, lmaxï€ ï€½762nm, and lmax=945nm, respectively. Mixtures of them will be colored black, which is consistent with observable black coloration of PbI64- alignments with MeNH3+ in amorphous solute state. It is further verified that PbI64- undergoes van der Waals and Coulomb interactions both with electron accepting layers, i.e., nc-TiO2 in PSC of nc-TiO2/MeNH3PbI3/spiro-OMeTAD and with electron donating layer, i.e., spiro-OMeTAD in the PSC. The molecular orbital structure and electrostatic potential map verifies formation of tight interaction between them. The electron density-based alignment PbI64- validates unidirectional electron transport at both interfaces, resulting in high open-circuited voltage (Voc) of ~1.0 eV in PSC. In addition, the semi-conducting sensitizing layer of PbI64-/MeNH3+ components validates excellent short-circuited photocurrent (Jsc), and respectable fill factor of PSC. The PbI64--aligned solar cell will be regarded as a kind of quantum dot solar cell
