# Effect of π-spacer moieties coupled to a porphyrin/PC70BM donor–acceptor for promising organic photovoltaic properties: a DFT study

## TL;DR

This study designs porphyrin-based molecules for organic solar cells and finds that they have improved photovoltaic properties.

## Contribution

The novelty lies in using π-spacer moieties with a porphyrin/PC70BM donor–acceptor system to enhance organic photovoltaic performance.

## Key findings

- Designed molecules showed reduced band gaps (3.86–4.07 eV) compared to the reference (4.13 eV).
- FF1 exhibited the best photovoltaic properties, including low reorganization energies and high absorption wavelengths.
- Molecules displayed bathochromic shifts and intramolecular charge transfer, making them suitable for organic solar cells.

## Abstract

The present study involved the design of porphyrin-based molecules (FF1–FF4) with a D1-π-D2-π-D1 configuration. This was accomplished by adding distinct π-spacers to a reference donor molecule. This research employs DFT and time-dependent DFT analyses at the CAM-B3LYP/6-31G(d,p) level to explore optoelectronic and photovoltaic characteristics. The designed molecules showed a decrease in the band gap, with values ranging from 3.86 to 4.07 eV, compared to R (4.13 eV). Furthermore, the molecules displayed bathochromic shifts in the visible region in the gas phase (419.13–435.58 nm) and in the chlorobenzene phase (442.41–457.89 nm) relative to R (410.82 and 436.41 nm, respectively). Moreover, evidence of intramolecular charge transfer (ICT) was obtained by employing DOS and TDM graphical maps. The presence of naphthalene groups at the terminus of the porphyrin core may facilitate charge mobility. FF1 has been proven to be the most promising candidate, exhibiting exceptional photovoltaic properties. Among these characteristics are a minimum band gap of 3.86 eV, extremely low reorganization energies for electrons (λe = 0.0030 eV) and holes (λh = 0.0022 eV), maximum absorption wavelengths of 435.58 nm in gas phase and 457.89 nm in chlorobenzene, and a preferred open-circuit voltage (VOC) of 1.59 eV in comparison to the PC70BM LUMO acceptor. All of these characteristics are present. The results show that the molecules under investigation are good candidates for organic solar cell (OSC) applications as donor materials and hole-transport materials, and they perform very well in photovoltaic studies.

The present study involved the design of porphyrin-based molecules (FF1–FF4) with a D1-π-D2-π-D1 configuration.