# Effect of the Number of Phenylcarbazole Units Adorned to the Silicon Atom for High Triplet Energy with High Charge Mobility

## TL;DR

Adding more phenylcarbazole units to a silicon atom in organic thin films improves charge mobility while keeping high triplet energy.

## Contribution

The study shows how increasing phenylcarbazole units enhances charge mobility without reducing triplet energy in organic thin films.

## Key findings

- Charge mobility increased from 1.32 × 10−4 to 1.16 × 10−3 cm²/Vs with more phenylcarbazole units.
- High triplet energy of 3.01 eV was maintained despite increased mobility.
- Intramolecular charge transfer reduced reorganization energy, improving mobility.

## Abstract

Increasing the number of phenylcarbazole (PC) units attached to the silicon atom in organic solid-state thin films led to a remarkable enhancement in charge mobility. Specifically, the charge mobility values exhibited an increase from 1.32 × 10−4 cm2/Vs for 3PCBP to 4.39 × 10–4 cm2/Vs for 2MCBP, ultimately reaching 1.16 × 10–3 cm2/Vs for MCBP. Notably, these enhancements were achieved while maintaining a high triplet energy of 3.01 eV. DFT calculations on the spin density distribution provided insights into the nature of the improved mobility while preserving the triplet energy. The accuracy of the DFT calculations was validated by comparing the results with experimental data from photoemission spectroscopy (PES). Mobility measurements, as contemplated by DFT, allowed for a comprehensive understanding of the factors influencing enhanced mobility while keeping the triplet energy constant. This study suggested that intramolecular charge transfers played a crucial role in reducing reorganization energy, showing an inverse dependence on the number of PCs. Consequently, it was inferred that the manipulation of PC units could effectively optimize charge transfer mechanisms, offering a promising avenue for tailoring organic thin films with improved electronic properties.