Design rules for high-efficiency quantum-dot-sensitized solar cells: A multilayer approach

The effect of multilayer sensitization in quantum-dot (QD)-sensitized solar cells is reported. A series of electrodes, consisting of multilayer CdSe QDs were assembled on a compact TiO ₂ layer. Photocurrent measurements along with internal quantum efficiency calculation reveal similar electron collection efficiency up to a 100 nm thickness of the QD layers. Moreover, the optical density and the internal quantum efficiency measurements reveal that the desired surface area of the TiO ₂ electrode should be increased only by a factor of 17 compared with a compact electrode. We show that the sensitization of low-surface-area TiO ₂ electrode with QD layers increases the performance of the solar cell, resulting in 3.86% efficiency. These results demonstrate a conceptual difference between the QD-sensitized solar cell and the dye-based system in which dye multilayer decreases the cell performance. The utilization of multilayer QDs opens new opportunities for a significant improvement of quantum-dot-sensitized solar cells via innovative cell design.