The Effects of Chromophore Halogenation on Reliability of UV–Absorbing Organic Transparent Photovoltaics

Transparent solar cells can be integrated into surfaces of buildings and vehicles to provide point-of-use power without impacting aesthetics. Though most demonstrations of transparent photovoltaics (TPVs) have focused on absorbing near-infrared photons, UV-harvesting TPVs can be far more transparent and better suited for low-power electronics that prioritize aesthetics. Organic solar cells employing contorted hexabenzocoronene and its derivatives as chromophores have been shown good candidates for this application due to their strong UV light absorption, visible transparency, modular synthesis, and chemically tunable electronic structure, and large-area scalability. In this presentation, we report the operational stability of such devices. We find the solar cells that include peripherally halogenated chromophores degrade rapidly and exhibit S-shape <i>J-V</i> curves upon photo-exposure during aging experiments, while control cells employing non-halogenated derivatives as donors with archetype C₇₀ as an acceptor to show excellent stability. We find that this degradation is primarily caused by aggregation of the halogenated acceptor materials during operation, which generates voids at the active layer-electrode interface. These results suggest that halogenation of chromophores, a commonly utilized molecular modification method, can negatively impact the stability of materials and reduce device operational lifetimes, which should be assessed as part of the material design process.