A novel low‐bandgap conjugated polymer (PTPTB, Eg = ∼ 1.6 eV), consisting of alternating electron‐rich N‐dodecyl‐2,5‐bis(2′‐thienyl)pyrrole (TPT) and electron‐deficient 2,1,3‐benzothiadiazole (B) units, is introduced for thin‐film optoelectronic devices working in the near infrared (NIR). Bulk heterojunction photovoltaic cells from solid‐state composite films of PTPTB with the soluble fullerene derivative [6,6]‐phenyl C61 butyric acid methyl ester (PCBM) as an active layer shows promising power conversion efficiencies up to 1 % under AM1.5 illumination. Furthermore, electroluminescent devices (light‐emitting diodes) from thin films of pristine PTPTB show near infrared emission peaking at 800 nm with a turn on voltage below 4 V. The electroluminescence can be significantly enhanced by sensitization of this material with a wide bandgap material such as the poly(p‐phenylene vinylene) derivative MDMO‐PPV.

Dye-sensitized TiO 2 solar cells have attracted considerable interest since it was shown that conversion efficiencies of up to 10 % can be reached. [1,2] In recent years successful attempts have been made to replace the liquid electrolyte solution in these cells with elastomeric polymers or gelators filled with an ionic redox couple, [3±7] and by p-type organic or inorganic semiconductors, [1±3,8] resulting in conversion efficiencies of up to 3.2 %.[4] A particularly attractive approach is to replace the dye and liquid electrolyte with a single conjugated polymer which combines the functions of light absorption and hole transport.[5±9] However, one of the problems associated with conjugated polymers and nanocrystalline TiO 2 (nc-TiO 2 ) is the inefficient filling of the pores of the TiO 2 matrix, especially because small (~20 nm) pores are required to ensure that the majority of photoexcited charge carriers in the polymer reach the interface with TiO 2 where charge separation occurs. In practice, hybrid polymer/nc-TiO 2 photovoltaic devices are now limited by charge transport (incomplete filling) and charge generation (large pores).Here, we present a new and simple procedure for preparing bulk-heterojunction hybrid organic±inorganic solar cells in which a continuous interpenetrating network of TiO 2 is created inside a thin conjugated polymer film. The characteristic distance of the polymer:TiO 2 bulk-heterojunction is in the nanometer range and results in an efficient formation of photoinduced charges that can be collected when the film is incorporated in a photovoltaic device.To prepare the bulk-heterojunction, a dry tetrahydrofuran (THF) solution containing poly[2-methoxy-5-(3¢,7¢-dimethyloctyloxy)-p-phenylene vinylene] (MDMO-PPV; Scheme 1) and titanium(IV) isopropoxide (Ti(OC 3 H 7 ) 4 ), a precursor for TiO 2 , is spin-coated on a substrate to obtain a mixed film with a thickness of about 50±70 nm. Subsequent conversion in the dark of the Ti(OC 3 H 7 ) 4 precursor via hydrolysis in air results in the formation of a TiO 2 phase in the polymer film. As a consequence of the presence of TiO 2 , the bulk-heterojunction film becomes resistant to scratching and can no longer be wiped off the substrate. Furthermore, the polymer in the bulk-heterojunction no longer dissolves in organic solvents such as toluene.X-ray photoelectron spectroscopy (XPS) has been used to assess the formation of TiO 2 under these conditions by examining the C/Ti and Ti/O elemental ratios, which are expected to change from 12:1 and 1:4 in Ti(OC 3 H 7 ) 4 to 0:1 and 1:2 in TiO 2 . Because the elemental composition is strongly influenced by the polymer in the film, the conversion of Ti(OC 3 H 7 ) 4 into TiO 2 under ambient conditions (in the absence of polymer) was also studied and compared to a film of TiO 2 prepared via the same procedure followed by conversion at high temperature (400 C) in air for 30 min. Both samples were then placed under vacuum overnight. The XPS spectra of the low-and high-temperature converted pure Ti(OC 3 H 7 ) 4 f...

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. Time-resolved infrared-absorption study of photoinduced charge transfer in a polythiophenemethanofullerene composite film. Physical Review B, 61(15), 9917-9920.