Designing intramolecular singlet-fission materials using indeno[1,2-b]fluorene dimers: A DMRG and TDDFT study

TL;DR

This study uses DMRG and TDDFT methods to analyze indeno[1,2-b]fluorene dimers, demonstrating their potential for intramolecular singlet-fission to improve solar cell efficiency, independent of crystal packing.

Contribution

It provides a detailed computational analysis of indeno[1,2-b]fluorene dimers, showing their suitability for intramolecular singlet-fission based on energy conditions and orbital localization.

Findings

All studied dimers satisfy energy conditions for SF.

Orbital localization supports entangled triplet-triplet state formation.

Results align with experimental data.

Abstract

Low-lying excited states for indeno[1,2-b]fluorene homo dimers with or without benzene spacers are calculated using the Density Matrix Renormalization group (DMRG) approach within Pariser-Parr-Pople (PPP) model Hamiltonian. DMRG calculations suggest that all the dimers studied here satisfy the essential energy conditions for SF. SF is a multiexciton generation process. As it is spin allowed, the process is very fast. By generating multiple exciton at a time SF underestimate SQ limit to enhance photo-conversion efficiency of single junction solar cells. Frontier orbital calculation through Density Functional Theory (DFT) depicts orbital localization of triplets on either side of the covalent spacers. Which supports the entangled triplet-triplet state $^1(TT)$. Here the process is intramolecular (iSF), which has many advantages over the intermolecular (xSF) process, as in intermolecular process the SF process is highly dependent on the crystal packing, defects, dislocations etc. The entangled $^1(TT)$ state for xSF is localized on both of the chromophores, thus the appropriate crystal packing is essential for xSF. However iSF does not depend on the crystal packing. Our DMRG calculation and TDDFT calculation are in well agreement with experimental results found in the literature. Thus indeno[1,2-b]fluorene homo dimers can be applicable in iSF application.