Feasibility of p-Doped Molecular Crystals as Transparent Conductive Electrodes via Virtual Screening

Transparent conducting materials are an essential component of optoelectronic devices. It is proven difficult, however, to develop high-performance materials that combine the often-incompatible properties of transparency and conductivity, especially for p-type-doped materials. In this work, we have employed a large set of molecular semiconductors extracted from the Cambridge Structural Database to evaluate the likelihood of transparent conducting material technology based on p-type-doped molecular crystals. Candidates are identified imposing the condition of high highest occupied molecular orbital (HOMO) energy level (for the material to be easily dopable), high charge carrier mobility (for the material to display large conductivity when doped), and a high threshold for energy absorption (for the material to absorb radiation only in the ultraviolet). The latest condition is found to be the most stringent criterion in a virtual screening protocol on a database composed of structures with sufficiently wide two-dimensional (2D) electronic bands. Calculation of excited-state energy is shown to be essential as the HOMO-lowest unoccupied molecular orbital (LUMO) gap cannot be reliably used to predict the transparency of this material class. Molecular semiconductors with desirable mobility are transparent because they display either forbidden electronic transition(s) to the lower excited states or small exchange energy between the frontier orbitals. Both features are difficult to design but can be found in a good number of compounds through virtual screening.

Automated summary

Transparent conducting materials are crucial for optoelectronic devices, but it is challenging to develop high-performance materials that are both transparent and conductive, especially for p-type-doped materials. In this study, a large set of molecular semiconductors from the Cambridge Structural Database were evaluated to identify potential transparent conducting materials based on p-type-doped molecular crystals. Candidate materials were selected based on high HOMO energy levels, high charge carrier mobility, and a high threshold for energy absorption. Additionally, the calculation of excited-state energy was found to be essential for accurately predicting material transparency. Through virtual screening, molecular semiconductors with desirable mobility and transparency can be discovered.