DFT and TDDFT investigation of four triphenylamine/phenothiazine-based molecules as potential novel organic hole transport materials for perovskite solar cells

Hole transport materials (HTMs) based on conductive organic molecules are crucial components to prepare highly efficient perovskite solar cells (PSCs). To overcome the limitations arising from the use of the most common Spiro-OMeTAD, hindering large-scale PSCs production, alternative HTMs are highly desirable. Therefore, several fully organic molecules mainly based on triphenylamine moieties have already been proposed. However, there is still room for the development of more efficient and easily obtainable HTMs. Within this framework, the in silico design of four novel triphenylamine/phenothiazine-based HTMs (HTM1-4) is presented here. Their electronic and molecular properties have been investigated by means of Density Functional Theory (DFT) and Time Dependent DFT (TDDFT) methods and the results have been compared to those of Spiro-OMeTAD and a previously reported phenothiazine-based HTM (PTZ2). The analysis suggests that HTM1-4 fulfil the requirements that enable hole extraction and transport processes in PSCs. Therefore, they should be considered as possible alternatives to Spiro-OMeTAD for the construction of potentially efficient PSCs.