Design, synthesis and theoretical simulations of novel spiroindane-based enamines as p-type semiconductors

The search for novel classes of hole transporting materials (HTMs) is a
very important task in advancing the commercialization of various
photovoltaic devices. Meeting specific requirements, such as thermal
stability, appropriate energy levels, and charge-carrier mobility, is
essential for determining the suitability of an HTM for a given
application. In this work, two spirobisindane-based compounds, bearing
terminating hole transporting enamine units, were strategically designed
and synthesized using commercially available starting materials. The
isolated compounds exhibit sufficient thermal stability and are amorphous
with high glass-transition temperatures (>150⁰C), minimising the
risk of direct layer crystallization. V1476 stands out with the highest
zero-field hole-drift mobility, approaching 1×10-5 cm2Vs-1. To assess the
compatibility of the HOMO energy levels of the spirobisindane-based HTMs
in solar cells, the solid-state ionization potential (Ip) was measured by
the electron photoemission in air of the thin-film method. The favourable
morphological properties, energy levels, and hole mobility in combination
with a simple synthesis make V1476 and related compounds promising
materials for HTM applications in antimony-based SCs and
triple-cation-based perovskite SCs.