Nanoscale Interaction Between CdSe or CdTe Nanocrystals and Molecular Dyes Fostering or Hindering Directional Charge Separation

Abstract

Dye is coabsorbed with CdSe nanocrystals (see image), strongly increasing the amount of charge injected into TiO2 from CdSe nanocrystals and providing an additional degree of control over the electron charge‐transfer process. This could have important implications in the development of supracollectors with enhanced absorption and charge‐separation properties for photovoltaic devices.

Ultrafast characterization of the electron injection from CdSe quantum dots and dye N719 co-sensitizers into TiO2 using sulfide based ionic liquid for enhanced long term stability

“…These results suggest the dye regeneration action affecting the QD injection rate, since the hole is quickly removed from the QD the photoexcited electron does not recombine before being injected. The results obtained in this work explain the previous results on surface photovoltage 15,19 (SPV) or on photoluminescence 16 (PL) for co-sensitized electrode. The net improvement of the amount of photoinjected electrons into TiO 2 , observed by SPV, or the PL quenching for co-sensitized electrodes was due to an improvement of charge separation efficiency that avoids the charge recombination before injection.…”

“…These materials present a favorable type II alignment (cascade structure) which promotes the electron injection and hole extraction efficiencies. 15,16 Electrodes coated with a single sensitizer (CdSe or N719) and with both sensitizers (first CdSe and N719 over it) have been analyzed.…”

“…8,9 In addition, semiconductor QDs are excellent building blocks for the design of light supracollecting structures by the synergetic combination of different types of QDs, 10,11 or QDs and dyes. [12][13][14][15][16][17][18][19][20] Different QDs and dye hybrid systems have been explored with the aim to exploit their interacting proprieties. In this heterostructures, performance can arise from the fast scavenging of photogenerated holes in quantum dots by a molecular dye.…”

“…Most recently, solvent-free ionic liquid based electrolytes containing sulfide/polysulfide redox couple compatible with inorganic sensitizers have been reported, being a promising alternative for this type of efficient supracollector nanocomposites, and adding the advantages of ionic liquid electrolytes, such as, nonvolatility, non-flammability and high ionic conductivity, among others. 26 We have studied, in precedent works, the charge separation in hybrid sensitized electrodes with surface photovoltage 15,19 (SPV) and photoluminescence 16 (PL). These studies are completed in this work.…”

“…This process can outbalance the competition between the electron transfer into the TiO 2 and the internal relaxation of the quantum dot excited state, leading to a better charge separation and higher electron injection yields. 15,19 Simultaneously, the combined use of QD and dye enhances the light harvesting wavelength range due to the combined absorption of the two assembled sensitizers. 12,17,18 Although hybrid sensitized systems appear promising, only few examples have been…”