  The chemical stability of nonfullerene acceptor (NFA) is the Achilles' heel
of the research on state-of-the-art organic solar cells (OSC). The fragility of
the NFA is essentially due to the weak bond that links the central donor core
of the molecules with their acceptor moieties at the edges. Here we proposed
the replacement of thiophene at the outer-core position of traditional NFAs for
tellurophene, a hitherto unexplored modification. Since tellurium is a
distinctive element among chalcogens, the basic features of Te compounds cannot
be deduced straightforwardly from the properties of their lighter analogues, S
and Se. The modeled Te-based NFAs presented interesting features like stronger
intra- and intermolecular interactions induced by a distinctive secondary bond
effect between the end acceptor moiety and the outer chalcogen atom. This
design strategy resulted in stiffer molecules with red-shifted absorption
spectra and less susceptible to degradation verified through stress tests and
vibrational spectra analysis. Besides that, a weakened exciton binding energy
has been found, opening the possibility of blends with a lower driving force.
Our results shed light on several aspects of selenation and telluration of
traditional NFAs, providing valuable insights into the possible consequences
for OSCs applications.
