Theoretical insight into the influence of different molecular design strategies on photovoltaic properties for a series of POM-based dyes applied in dye-sensitized solar cells

Abstract

Theoretical calculations based on density functional theory (DFT) and time-dependent DFT (TD-DFT) are employed to investigate a series of polyoxometalate (POM)-based dyes by adopting different molecular design strategies, such as the introduction of a second donor or a change in π linker units. The π linker effects of boron dipyrromethene (BODIPY) derivatives such as BODIPY-dihydrofuran (BODIPY-F) and BODIPY-dihydrothiophene (BODIPY-T) were analyzed to understand their photophysical and photoelectrochemical properties. Compared to dye 1 with one triphenylamine donor, dye 2 with two triphenylamine donor groups has better harvest sunlight ability due to the broader absorption spectra. Dye 4 with the BODIPY-T π linker not only exhibits the broadest absorption spectra, largest ICT parameters due to the smallest aromaticity of BODIPY-T, largest short-circuit photocurrent density governed by the driving force for electron injection, and the largest open-circuit photovoltage connected with the electron recombination process and the energy shift of the conduction band (CB) among dyes 1–4, but also possesses the lowest interaction energy for the most stable dimer configuration resulting from the weakest van der Waals interaction, which can reduce dye aggregation. Dyes 1–4 attached to the TiO₂ (101) surface were modeled to estimate the interfacial electron transfer performance of DSSCs, and dyes 2–4 could quickly inject electrons into the semiconductor CB. The qualitative structure photovoltaic property relationship thus obtained may serve as a guide to tailor-design various properties of POM-based dyes for application in DSSC devices.