Hybrid optimizing optoelectronic properties: structural analysis of silicon and germanium-modified PCPDTBT polymers

Abstract

The molecular structure and optoelectronic characteristics of PCPDTBT polymers modified with silicon (PSBTBT) and germanium (PGeDTBT) substituents were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) computational methods. The results demonstrate that incorporating inorganic elements such as silicon or germanium into the polymer backbone significantly enhances structural, electronic, and optical properties. When silicon and germanium are added, the bridge length increases (1.453858 Å for PSBTBT and 1.453544 Å for PGeDTBT compared to 1.452408 Å for PCPDTBT). This structural modification enhances chain rigidity and improves intramolecular charge transfer (D_CT PGeDTBT > D_CT PCPTBT > D_CT PSBTBT), promoting greater electron mobility. The bandgap energies increase slightly to 1.71 eV for PSBTBT and 1.70 eV for PGeDTBT, up from 1.62 eV for PCPDTBT, facilitating broader absorption in the visible spectrum. Optical analysis reveals that PSBTBT and PGeDTBT exhibit two main absorption peaks: 300 nm and 682 nm for PSBTBT and 325 nm and 715 nm for PGeDTBT, while the maximum absorption peak of PCPDTBT is located at 758 nm. The exciton binding energy (EB) also increases, from 0.32 eV for PCPDTBT to 0.38 eV for PSBTBT and 0.41 eV for PGeDTBT resulting in more efficient charge separation. These enhancements, along with higher open-circuit voltages (1.29 eV for PSBTBT and 1.26 eV for PGeDTBT compared to 1.22 eV for PCPDTBT), make these hybrid polymers promising candidates for organic photovoltaic applications. The findings provide valuable insights into structure–property relationships of novel organic–inorganic hybrid materials, paying the way for advancements in organic photovoltaic technology.

Graphical abstract