We have explored the opto-electronic properties of a new series of hole-transport materials based on main-chain triphenylamine-based poly(azomethine)s. 4,4 0 -Diaminotriphenylamine (TPA) was polymerized under benign conditions with either terephthalaldehyde (TPA-14Ta), 2,5-thiophenedicarboxaldehyde (TPA-25Th) or 1,3-isophthalaldehyde (TPA-13Iso) to yield polymers with an M n of 5700-16 000 g mol À1 . Despite the non-linear, or 'kinked', backbone geometry, all polymers form lyotropic solutions in chloroform and this liquid crystal (nematic) ordering could be maintained in the solid film after spin casting. All polymers exhibit high glass-transition temperatures (T g > 250 C) and display outstanding thermal stabilities, i.e. 5% wt loss in excess of 400 C under nitrogen. The HOMO and LUMO energy levels of these polymers were in the range of 5.0-5.3 and 2.4-3.3 eV below the vacuum level, respectively. Introduction of a thiophene heterocycle (TPA-25Th) resulted in a material with a low optical band-gap of approximately 2.0 eV, whereas TPA-14Ta and TPA-13Iso showed optical band gaps of 2.3 and 2.6 eV, respectively. A photovoltaic device based on a TPA-25Th/PCBM blend (1 : 3) showed an EQE of 20% at 500 nm. Under simulated sunlight, the device gives an open-circuit voltage of 0.41 V, a short-circuit current of 1.23 mA cm À2 and a fill factor of 0.24, leading to a power conversion efficiency of 0.12%.

Based on 80 884 events, we obtained the matrix element squared for the decay 7 . r '~ rO:

The dye-sensitized solar cell, based on a wide-bandgap semiconductor photosensitized with an organic dye, is an attractive low-cost alternative to conventional silicon-based solar cells.[1] Absorption of a photon by the dye results in the formation of a strongly bound electron-hole pair, also referred to as an exciton. A key feature of the dye-sensitized solar cell is that efficient exciton decay into separate charge carriers can only occur at the interface between the dye and the semiconductor, leading to injection of an electron into the conduction band of the semiconductor. [2] Since O'Regan and Grätzel reported an efficiency over 10 % for a cell based on an interpenetrating network of dye-coated nanocrystalline TiO 2 particles and a liquid electrolyte containing a iodide/ triiodide redox mediator, [3] the use of nanostructured films in photovoltaic devices has been studied extensively. Due to complications involved in the use of a liquid electrolyte, [4] there is presently great interest in the development of all-solid-state organic/inorganic solar cells. For these cells a maximum performance of 4 % has been realized so far.[5] The use of nanostructured networks avoids the necessity of long-range exciton diffusion through the dye layer. However, in such systems electron transport is hampered by trapping at surface defects.[6] The difficulties involved in electron transport can be avoided by using a bilayer configuration consisting of a bulk semiconductor and a relatively thick dye layer. In order to realize efficient charge separation in such a bilayer configuration, the distance excitons are able to cover by diffusion (exciton diffusion length) needs to be equal to or larger than the light penetration depth, which has a typical value of 50-100 nm. The exciton diffusion length in molecular organic dye layers is usually of the order of only a few nanometers, [7][8][9][10] although Nature shows that it is possible to transport excitation energy efficiently over considerably longer distances. An example is found in the photosynthetic apparatus of purple bacteria, which consists of reaction centers and two types of lightharvesting complexes: LHI and LHII. The light-harvesting complexes consist of chlorophyll and carotenoid molecules, kept in place by proteins. [11][12][13] The presence of chlorophyll molecules leads to a strong light absorption. In addition, the structure of the light-harvesting complexes provides a highly efficient pathway for exciton transport; 80-90 % of the excitons formed on light absorption are transferred to the reaction center, where charge separation occurs.[14] For a few molecular dye systems only, exciton diffusion lengths considerably longer than a few nanometers have been realized in vacuum thermal deposited layers. [15,16] However, the expensive elaborate deposition technique makes these layers commercially less attractive and could only be applied for a few dye materials. Chlorophylls and their analogues are attractive candidates for application in dye-sensitized solar cells, [17,1...

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