Asymmetric flexible strategies enable liquid crystalline transitions during thermal annealing of the device in organic solar cells

Using liquid crystalline (LC) small molecule donors with good crystallinity and ordered molecular packing to regulate the morphology of an active layer has emerged as an effective strategy. We employed an asymmetric flexible strategy to synthesize two LC small molecule donors LCS6 and LCS8, and the nematic LC state of the two molecules was clearly determined using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Under the action of long alkoxy side chains, the LC transition temperature (130 °C) was successfully reduced to the commonly used temperature for thermal annealing (TA), which facilitates a direct study of the relationship between the LC properties and device performance. The morphology analysis suggests that a notable reduction in the phase separation scale and aggregation after TA may be attributed to the self-assembly behavior inherent to LC materials. Liquid crystalline (LC) small molecule donors synthesized using asymmetric flexible strategies exhibited LC transition upon thermal annealing (TA) at 130 °C.