Abstract
We present a comparison of the photovoltaic activity of organic solar cells (OPVs) based on vacuum-deposited and solvent-annealed titanyl phthalocyanine (TiOPc) donor layers with C60 as the electron acceptor, where the TiOPc donor layer exists in three different polymorphic forms: TiOPc included the “as-deposited” form, with a Q-band absorbance spectrum reminiscent of the phase I polymorph, and films subjected to solvent annealing which systematically increased the fraction of either the phase II (α-phase) or the phase III (γ-TiOPc) polymorphs. As-deposited TiOPc/C60 heterojunctions showed open-circuit photopotentials (VOC) of ca. 0.65 V, with estimated AM 1.5G efficiencies of ca. 1.4%. Partial conversion of these thin films to their phase II or phase III polymorphs significantly enhanced the short-circuit photocurrent (JSC), as a result of (i) texturing of the TiOPc layers (ca. 100 nm length scales) and (ii) enhancements in near-IR absorptivity/photoelectrical activity. All TiOPc/C60 heterojunctions, cha...
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