Exploring the impact of electron acceptor tuning in D-pi-A '-pi-A photosensitizers on the photovoltaic performance of acridine-based DSSCs: A DFT/TDDFT perspective

Nine novel organic molecules with D-rc-A'-rc-A motifs, designated as (Ac-T-Qs-T-CA) and (Ac-T-Bx-T-CA), were proposed as potential photosensitizers for use in dye-sensitized solar cells (DSSCs). These novel organic photosensitizers are comprised of an acridine electron donor (Ac) and a thiophene rc-spacer (T), while the electron acceptor unit (A') is either a substituted quinoxaline (Qs) or a benzo[2,5]diazole-1-heteroatom (Bx), and the anchoring group (A) is 2-cyanoacrylic acid (CA). The influence of electron acceptor (A') moieties on the electronic, photophysical, thermodynamic and photovoltaic properties of the photosensitizers was analyzed using DFT and TD-DFT calculations. The MM3 force field and CONFLEX conformational search methods were employed to study all possible structural conformations of the photosensitizers. The goal was to identify the lowest energy conformer and gain a better understanding of how the structure conformation and torsional angles of (Ac-T-Qs-T-CA) and (Ac-T-Bx-T-CA) compared to the reference photosensitizer RK1 affect electron injection ability and overall performance of DSSCs. The thermodynamic analysis revealed that the photosensitizers (Ac-TQ2,3-diOMe-T-CA) and (Ac-T-BtA-T-CA), which contain a 2,3-dimethoxyquinoxaline (Q2,3-diOMe) and a benzo[d] [1,2,3]triazole (BtA) acceptor moieties, respectively, exhibit a noteworthy enhancement in their electroninjection free energy (AGinj) and a reduction in their recombination-free energy (AGrec) values, leading to an improvement in the overall photovoltaic properties of the solar cell when compared to the other photosensitizers. The photovoltaic characteristics of the photosensitizers showed that the photosensitizer (Ac-T-Q2,3-diOMe-T-CA) demonstrated the highest values of open-circuit photovoltage (Voc = 1.41 eV) and light harvesting efficiency (LHE = 0.80 eV) compared to the other (Ac-T-Qs-T-CA) photosensitizers. Similarly, (Ac-T-BtA-T-CA) photosensitizer demonstrated the highest Voc (1.08 eV) and LHE (0.75 eV) among (Ac-T-Bx-T-CA) photosensitizers. The photovoltaic performance of these new photosensitizers outperformed the reference RK1 photosensitizer, which only achieved a Voc of 1.2 eV and LHE of 0.61 eV. Finally, the electronic structures and optical properties of photosensitizers adsorbed on the TiO2 surface were studied to provide more accurate information about their adsorption on the semiconductor surface.

Automated summary

This study proposed nine novel organic molecules as potential photosensitizers for dye-sensitized solar cells (DSSCs). The influence of electron acceptor moieties on the physical and photovoltaic properties of the photosensitizers was analyzed. The results showed that two of the photosensitizers exhibited enhanced electron injection and reduced recombination, leading to improved overall photovoltaic performance.