We demonstrate that photogenerated excitons in semiconducting carbon nanotubes (CNTs) can be efficiently dissociated by forming a planar heterojunction between CNTs wrapped in semiconducting polymers and the electron acceptor, C(60). Illumination of the CNTs at their near-infrared optical band gap results in the generation of a short-circuit photocurrent with peak external and internal quantum efficiencies of 2.3% and 44%, respectively. Using soft CNT-hybrid materials systems combining semiconducting small molecules and polymers, we have fabricated broad-band photodetectors with a specific detectivity >10(10) cm Hz(1/2) W(1-) from lambda = 400 to 1450 nm and a response time of tau = 7.2 +/- 0.2 ns.

We demonstrate that solvent vapor annealing of small molecular weight organic heterojunctions can be used to independently control the interface and bulk thin-film morphologies, thereby modifying charge transport and exciton dissociation in these structures. As an example, we anneal diphenyl-functionalized squaraine (DPSQ)/C(60) heterojunctions before or after the deposition of C(60). Solvent vapor annealing of DPSQ before C(60) deposition results in molecular order at the heterointerface. Organic photovoltaics based on this process have reduced open circuit voltages and power conversion efficiencies relative to as-cast devices. In contrast, annealing following C(60) deposition locks in interface disorder found in unannealed junctions while improving order in the thin-film bulk. This results in an increase in short circuit current by >30% while maintaining the open circuit voltage of the as-cast heterojunction device. These results are analyzed in terms of recombination dynamics at excitonic heterojunctions and demonstrate that the optimal organic photovoltaic morphology is characterized by interfacial disorder to minimize polaron-pair recombination, while improved crystallinity in the bulk increases exciton and charge transport efficiency in the active region.

We describe a hybrid planar-mixed heterojunction (PM-HJ) organic photovoltaic cell based on tetraphenyldibenzoperiflanthene (DBP) and C 70 with a power conversion efficiency of up to 6.4% 6 0.3%. Optimized cells consist of a DBP:C 70 mixed layer at a volume ratio of 1:8 and a 9-nm thick C 70 cap layer. The external quantum efficiency (EQE) in the visible of the PM-HJ cell is up to 10% larger than the mixed-HJ cell that lacks a C 70 acceptor cap layer. The improvement in EQE is attributed to reduced exciton quenching at the MoO 3 anode buffer layer surface. This leads to an internal quantum efficiency >90% between the wavelengths of k ¼ 450 nm and 550 nm, suggesting efficient exciton dissociation and carrier extraction in the PM-HJ cell. The power conversion efficiency under simulated AM 1.5G, 1 sun irradiation increases from 5.7% 6 0.2% for the mixed-HJ cell to 6.4% 6 0.3% for the PM-HJ cell, with a short-current density of 12.3 6 0.3 mA/cm 2 , open circuit voltage of 0.91 6 0.01 V, and fill factor of 0.56 6 0.01. V C 2013 American Institute of Physics. [http://dx.

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