Cohesion and adhesion of nanoporous TiO2 coatings on titanium wires for photovoltaic applications

The working electrode of a dye-sensitized photovoltaic fiber is constituted of a porous TiO2 coated titanium wire. The cohesion and adhesion of such a brittle oxide coating on the ductile metal substrate are identified as crucial factors in maintaining photovoltaic efficiency during textile manufacture and weaving operations. The influence of coating thickness on these factors has been investigated in the present work. The tensile mechanical characterization with in situ microscopic observations shows that two damaging processes are involved. For the smaller thickness, loss of adherence appears to be at the interface and inside the coating bulk. Cracks become visible in a random distribution in size and density and do not cross the entire coating circumference. Large patches of coating are still anchored on the wire. For the larger thickness no cohesive rupture in the coating bulk has been observed. The loss of adherence appears at the interface closed to the cracks and grows rapidly as the strain increases. Numerical investigations based on the finite element method permit to analyze the distribution and the combination of radial interfacial stress and circumferential coating stress and their influence on the observed damage

Mechanical integrity of dye-sensitized photovoltaic fibres

The development of photovoltaic (PV) devices based on dye-sensitized TiO2-coated Ti fibers has opened up exciting possibilities for novel PV textile applications. The cohesion and adhesion of the TiO2 layer are identified as crucial factors in maintaining PV efficiency during textile manufacture and weaving operations. The present work describes a systematic investigation of the corresponding damage mechanisms and their influence on the overall PV fiber performance during mechanical deformation. The results confirm that with proper control of the tension of the weft and in the warp, high PV efficiency woven textures are feasible using this technology

Morphology control in polycarbazole based bulk heterojunction solar cells and its impact on device performance

Incremental increase in dimethyl sulfoxide (or dimethyl formamide) in ortho-dichlorobenzene solution of poly [N -heptadecanyl-2,7-carbazole-alt-5,5- (4\u2032, 7\u2032 -di-2-thienyl- 2\u2032, 1\u2032, 3\u2032 -benzothiadiazole)] (PCDTBT) gradually reduces the polymer-solvent interaction, the attraction forces between polymer chains become more dominant, and the polymer chains adopt a tight and contracted conformation with more interchain interactions, resulting in a progressive aggregation in both solutions and films. This was used to fine tune the morphology of PCDTBT/ PC71 BM based solar cells, leading to improved domain structure and hole mobility in the active layer, and significantly improved photovoltaic performance. The power conversion efficiency increased from 6.0% to 7.1% on devices with an active area of 1.0 cm2. \ua9 2011 Crown.Peer reviewed: YesNRC publication: Ye

Effect of mixed solvents on PCDTBT:PC 70BM based solar cells

We investigated the effect of solvents on the morphology, charge transport and device performance of poly[N-9\u2033-hepta-decanyl-2,7-carbazole-alt-5,5- (4\u2032,7\u2032-di-2-thienyl-2\u2032,1\u2032,3\u2032-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C71-butyric acid methyl ester (PC 70BM) based solar cells. To carry out this investigation, chloroform and 1,2-dichlorobenzene were chosen as good solvents of the two compounds. Films prepared with chloroform exhibit larger domains than those prepared with 1,2-dichlorobenzene and their size increases with the amount of PC 70BM. Fine tuning of the domain size was realized by using a solvent of mixed chloroform and 1,2-dichlorobenzene. At a mixing ratio of 50%:50%, a power conversion efficiency of 6.1% was achieved on PCDTBT:PC 70BM (1:3) devices with an active area of 1 cm 2, under air mass 1.5 global (AM 1.5 G) irradiation at 100 mW/cm 2. \ua9 2011 Published by Elsevier B.V. All rights reserved.Peer reviewed: YesNRC publication: Ye