Traps, morphology and degradation in high efficiency polymer solar cells

Bulk heterojunction solar cells (BHJs) based on poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) can have internal quantum efficiencies approaching 100% but require active layers that are too thin to absorb more than ∼70% of the above bandgap light.[1] In this work, we demonstrate that PCDTBT films contain a high density of hole-traps, which correlate with polymer morphology and are important for BHJ performance.