We report a hybrid dye-sensitized solar cell consisting of double titania layers (top and bottom layers) stained with two dyes. A top layer fabricated on a glass was mechanically pressed with a bottom layer fabricated on a glass cloth. The glass cloth acts as a supporter of a porous titania layer as well as a holder of electrolyte. The incident photon to current efficiency (IPCE) curve had two peaks corresponding to those of the two dyes, which demonstrates that electrons are collected from both the top and bottom layers.

Fabrication and photovoltaic performances for flexible transparent conductive oxideless (TCO-less) flat and cylinder dye-sensitized solar cells (DSCs) are reported. The cylinder solar cell consists of a porous silicone tube, a protected stainless steel metal mesh (protected SUS mesh) working as a counter electrode, a gel electrolyte sheet, a dye/porous titania layer fabricated on a protected SUS mesh working as a anode, and a thermally shrinkable plastic tube, from the inside to the outside. The thermally shrinkable tube was used to reduce the gap between a cathode and an anode. In addition, a porous silicone tube was used for injecting electrolytes smoothly into the gel electrolyte layer. 5.08% efficiency (FF: 0.68; Voc: 0.68 V; Jsc: 11.07 mA∕cm 2 ) was observed. A flexible TCO-less flat DSCs with 6.1% efficiency which was improved by narrowing a gap between two electrodes is also reported.

A SnO 2 electrode is a promising candidate for a bottom electrode of dye-sensitized solar cells. One of the drawbacks is its low fill factor (FF). We clarified the cause of this low FF using our original hybrid cells consisting of carrier generation areas (a bottom layer consisting of TiO 2 /a dye layer) and carrier transport areas (a top layer consisting of SnO 2 with and without a dye layer). A large decrease in FF was observed only when the SnO 2 charge transport areas were covered by photo excited dyes, leading to the conclusion that back electron transfer reaction from SnO 2 to oxidized dyes is a major route for the charge recombination. This was also confirmed by electron lifetime and dark current measurements.

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