Improving the Performance of Dye-Sensitized Solar Cells

Abstract

Dye-sensitized solar cells have been investigated intensively during the last three decades. Nevertheless, there are still many aspects to be explored to further improve their performance. Dye molecules can be modified endlessly for better performance. For instance, steric groups can be introduced to slow down recombination reactions and avoid unfavorable aggregation. There is a need for more optimal dye packing on the mesoporous TiO₂ surface to increase light absorption and promote a better blocking effect. Novel redox mediators and HTMs are key elements to reach higher performing DSC as they can offer much higher output voltage than the traditional triiodide/iodide redox couple.

Keywords: cobalt-complex; electron lifetime; maximum power point; mesoporous TiO2; organic dyes; recombination.

Figure 1

Energy scheme and working mechanism of a dye-sensitized solar cell. Electron transfer reactions are indicated with numbers and arrows (green for forward, red for recombination) that are referred to in the text. The energy levels of different redox mediators are indicated (spiro-MeOTAD is a solid-state hole conductor).

Figure 2

Schematic electrical diagram of a dye-sensitized solar cell. A current generator give a photocurrent J_ph, which charges the capacitor. The current flow is through R_series + R_tr + R_ext and through R_rec.

Figure 3

Structures of efficient molecular sensitizers for DSC, with absorption maximum (λ_max) in nm, extinction coefficient (in 10³ M⁻¹ cm⁻¹) and zero-zero transition energy (E₀₋₀). LEG4 is structurally nearly identical to Y123, having butoxy-groups instead of hexoxy.

Figure 4

Effect of addition of a TPA electron donor to Co(bpy)₃ electrolyte in a DSC. (A) Charge extraction and (B) electron lifetime measurements as function of V_OC in a DSC with and without additive (Hao et al., 2016b).