Correlation between structural and optical characteristics of conjugated copolymers differing by a Si bridge atom

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Organic photovoltaic (OPV) devices offer a promising alternative to conventional solar cells.
• Copolymers are widely explored as electron donors in OPVs.
• Understanding charge transfer dynamics is crucial for optimizing OPV performance.

Purpose of the Study:

• To investigate the influence of heavy atoms, specifically silicon, on the electrical and morphological properties of photovoltaic devices.
• To compare the performance of PFO-DBT and its silicon-containing analogue, PSiF-DBT, as electron donors in OPVs.
• To elucidate the charge transfer mechanisms in these polymeric systems.

Main Methods:

• Charge transfer dynamics were evaluated using the core-hole clock method.
• Electronic structure and charge transfer properties were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT).
• Charge transfer rates were estimated using semiclassical Marcus/Hush theory.

Main Results:

• PSiF-DBT exhibits better polymer chain stacking, resulting in higher solar absorption at longer wavelengths and faster hole transfer rates.
• A faster electron transfer rate was observed at the PSiF-DBT/C60 interface compared to the PFO-DBT/C60 interface, attributed to a greater driving force.
• Organic photovoltaic devices utilizing PSiF-DBT demonstrated higher performance than those with PFO-DBT.

Conclusions:

• The incorporation of silicon into the copolymer structure (PSiF-DBT) significantly enhances photovoltaic device performance.
• Improved molecular stacking and favorable charge transfer dynamics are key factors contributing to the superior performance of PSiF-DBT-based devices.
• This study provides critical insights into optimizing OPV performance by tuning material properties and understanding charge transfer mechanisms.