Dye-sensitized solar cells (DSCs) belong to the third generation of solar cells, and present interesting advantages for photovoltaic applications such as low cost of fabrication and simplicity of manufacturing techniques. The highest efficiencies reported for DSCs are for cells using cobalt-based redox couples, which exhibit a high reduction potential, thus increasing the attainable photovoltage of the DSC. However, due to their more bulky nature, mass transport problems associated with the diffusion of the redox couple, mainly within the mesoporous layer, affect solar cell performance. As a result, the use of thinner mesoporous layers and high extinction coefficient dyes is advantageous for DSCs with a cobalt-based redox couple.

On the other hand, it has been stated that mass transport limitation may also become noticeable when the distance between electrodes is increased [1]. Interestingly, the highest reported efficiencies for DSCs with cobalt-based electrolyte are for solar cells with a small separation between the electrodes [2]; these cells were not sealed but were prepared pressing the electrodes together in order to reduce distance between electrodes and increase the fill factor.

In this work we present a sealed cell configuration with the lowest possible distance between electrodes, and report on the influence of the distance between electrodes on the performance of the solar cells. An important improvement of the fill factor, together with a decrease in the total resistance of the DSCs is observed for the cells sealed with this configuration, which improves the overall performance of the solar cells. A study of mass transport is presented, where it is shown that by reducing the distance between electrodes, the mass transport limitation corresponding to diffusion of the redox species in the bulk electrolyte is reduced.

REFERENCES.

1. Liu, W.; Hu, L.; Dai, S.; Guo, L.; Jiang, N.; Kou, D. The effect of the series resistance in dye-sensitized solar cells explored by electron transport and back reaction using electrical and optical modulation techniques. Electrochimica Acta 2010, 55, 2338-2343.

2. Kakiage, K.; Aoyama, Y.; Yano, T.; Oya, K.; Fujisawa, J.-i.; Hanaya, M. Highly-efficient dye-sensitized solar cells with collaborative sensitization by silyl-anchor and carboxy-anchor dyes. Chemical Communications 2015, 51, 15894-15897.