# Heterocyclic π-linkers for reduced energy dissipation in symmetrical IDT-core-based non-fullerene acceptors: a route to efficient organic solar cells

## TL;DR

This paper designs new non-fullerene acceptor molecules for organic solar cells to improve efficiency through better charge transfer and reduced energy loss.

## Contribution

Introduces heterocyclic π-linkers in IDT-based acceptors to achieve low bandgaps and efficient charge transfer for organic solar cells.

## Key findings

- IDT3 showed the lowest energy gap and exciton binding energy, indicating efficient photon harvesting and exciton dissociation.
- IDT1 had the highest dipole moment and open circuit voltage, suggesting strong charge separation and device stability.
- All new IDT derivatives displayed reduced bandgaps and improved charge mobilities compared to the reference molecule.

## Abstract

Achieving high power conversion efficiency (PCE) remains a major challenge in advancing organic solar cells (OSCs). In the field of organic photovoltaics (OPVs), substantial progress has been made in tuning molecular structures to enhance the PCE, yet innovative material design strategies targeting improved efficiency are still urgently needed. In this work, five novel A-π-D-π-A structured non-fullerene acceptor molecules (IDT1–IDT5) based on the IDT-ED-4F core are designed using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods to explore their optoelectronic properties in both gas and solvent phases. Among these, IDT3 exhibited the lowest energy gap (Eg = 1.35 eV), the lowest electron reorganization energy (λe = 0.00578 eV), and a high absorption maximum, indicating its strong potential for efficient photon harvesting and charge transport. IDT1 showed the highest dipole moment in both gas (6.81 D) and solvent phases (7.59 D), which enhances its charge separation capability, while its high fill factor (FF = 90.93%) suggests improved carrier collection and device stability. The theoretical open circuit voltage (Voc) calculations revealed that IDT1 achieved the highest Voc value of 1.40 V. Exciton binding energy (Eb) analysis indicated that IDT3 had the lowest Eb value (0.14 eV), implying efficient exciton dissociation. Transition density matrix (TDM) and reduced density gradient (RDG) analyses confirmed effective intramolecular charge transfer (ICT) and stable non-covalent interactions within these molecules. Compared to the reference IDT-ED-4F molecule, all newly designed derivatives displayed reduced bandgap (Eg), significant redshifted absorption, and enhanced charge mobilities. Overall, these results demonstrate that the newly developed IDT based molecules possess superior optoelectronic properties, establishing them as promising candidates for high efficiency next generation OSC applications.

Heterocyclic π-linker design in IDT-based acceptors enables efficient charge transfer, low bandgaps, and enhanced OSC performance.