Three derivatives of Poly(fluorene-alt-bithiophene) with straight or branched or both were synthesized.

The polymers and their binary blends with indene-C60 bisadduct are investigated regarding their general properties, morphology, photophysics, charge transport and photovoltaic device performance.

Straight side-chains promote aggregation and cause detrimental charge-trapping at grain boundaries.

Branched side-chains generate disorder, which is detrimental for charge transport across the conjugated polymer phase.

Combination of both side-chains is the ideal way to get the best morphology for an organic solar cell, preventing strong aggregation, but still allowing appropriate effective charge transport through well-distributed ordered nanophases.