Device performance is recognized to be generally sensitive to morphology in bulk heterojunction solar cells. Through the use of quantitative morphological measurements, it is demonstrated that devices based on benzodithiophene and fluorinated benzotriazole moieties constitute an exception to this design rule and exhibit a range of morphologies that yield similar high performance. In particular, the fill factor (FF) remains above 65% even with factor of two changes in domain size and factor of two changes in relative domain purity. Devices with active layer thicknesses of 250 nm are employed, which are capable of increasing optical absorption to produce high photocurrent. The general insensitivity to both morphology and thickness is likely related to the measured low equilibrium miscibility of fullerene in the polymer of 3-4%. The materials and processes investigated therefore provide insights into functional material design that yield increased processing latitude and may be more amenable to roll-to-roll processing.
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