  Solution-processed organic photovoltaics (OPV) have recently reached the
target 10% power conversion efficiency expected to signal their viable
commercialization as an inexpensive and scalable energy conversion technology.
However, obtaining devices with suitable long-term stability remains an
unsolved challenge. Here we present a new strategy to improve the thermal
stability of small-molecule-based bulk-heterojunction OPVs by including a
custom additive specifically designed to interact with the device active layer
components. Our results indicate that active layer degradation under continuous
thermal stress can be inhibited due to the formation of more robust thin film
microstructure with the additive present. Since our additive employs the
identical semiconductor core used in the active layer, but linked by aliphatic
chains into a flexible polymer, this straightforward strategy can reasonably be
applied to stabilize a wide variety of semiconducting small molecules in
solution-processed molecular OPVs, transistors and light emitting diodes.
