Investigation of Triphenylamine- based hole transport materials for Perovskite solar cells
Abstract
Perovskite photovoltaics is one of the most promising emerging photovoltaic technologies. The best performing perovskite solar cells (PSCs) with n-i-p structure currently employ the organic semiconductor Spiro-OMeTAD as a hole transporter. Spiro-OMeTAD requires a multi-step synthesis to produce, which negatively affects its viability as a material for large- scale fabrication. Furthermore, large amounts of resources are used, and large amounts of chemical waste is produced. Spiro-OMeTAD is based on the Spirobifluorene core, a structure where two fluorene systems are linked by a single atom. Preliminary results from our group indicate that materials containing only one fluorene system, usually referred to as “Half- Spiros” (HSs) can work as a replacement for Spiro-OMeTAD. These materials offer fewer synthetic steps, and therefore lower synthesis cost and environmental impact. However, HSs suffer from worse stability due to their lower glass transition temperature (Tg). Furthermore, the power conversion efficiency (PCE) is usually lower, due to worse alignment between the HOMO of the HS and the valence band (VB) of the perovskite. For this reason, we are developing new HSs with higher Tgs and better band alignment. DFT calculations will be used to predict the HOMO and LUMO energies, as well as the orbital geometries for different HS- structures. The knowledge gained this way can then be used to improve our understanding of the structure energy relationships in HSs, and to find suitable candidates for synthesis and experimental investigations.
Main Supervisor: Feng Gao, Linköping University
