Here, we demonstrate
the cooptimization of the interfacial fracture energy and power conversion
efficiency (PCE) of poly[<i>N</i>-9′-heptadecanyl-2,7-carbazole-<i>alt</i>-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]
(PCDTBT)-based organic solar cells (OSCs) by surface treatments of
the buffer layer. The investigated surface treatments of the buffer
layer simultaneously changed the crack path and interfacial fracture
energy of OSCs under mechanical stress and the work function of the
buffer layer. To investigate the effects of surface treatments, the
work of adhesion values were calculated and matched with the experimental
results based on the Owens–Wendt model. Subsequently, we fabricated
OSCs on surface-treated buffer layers. In particular, ZnO layers treated
with poly[(9,9-bis(3′-(<i>N</i>,<i>N</i>-dimethylamino)propyl)-2,7-fluorene)-<i>alt</i>-2,7-(9,9-dioctylfluorene)]
(PFN) simultaneously satisfied the high mechanical reliability and
PCE of OSCs by achieving high work of adhesion and optimized work
function