Electron Injection from a CdS Quantum Dot to a TiO₂ Conduction Band as an Efficiency Limiting Process: Comparison of QD Depositions between SILAR and Linker Assisted Attachment

Abstract

Sensitization of TiO 2 by semiconductor quantum dots (QDs) initiates a primary charge separation in semiconductor quantum dot sensitized solar cells (QDSSCs), and thus is a key fundamental process controlling their solar cell performance. However, despite extensive researches on QD deposition methods, correlation between the solar cell performance and charge transfer dynamics modulated by the different deposition method has rarely been studied. Here, we demonstrate influence of a CdS QD deposition method on their solar cell performance and charge transfer dynamics. Two deposition methods, (i) in-situ QD synthesis directly on the TiO2 surface using a Successive Ionic Layer Adsorption and Reaction (SILAR) method, SILAR-CdS/TiO 2 , and (ii) linker assisted attachment of pre-synthesized QDs on the TiO 2 surface, PSM-CdS/TiO 2 , were investigated. The electron injection efficiency of SILAR-CdS/TiO 2 is estimated to be 96%, while that of PSM-CdS/TiO 2 is 40~50%. The charge recombination dynamics are similar for both films. Therefore, the QDSSC efficiency is essentially controlled by the electron injection process from a CdS QD to the TiO 2 conduction band.

Photoinduced Charge Carrier Dynamics of Metal Chalcogenide Semiconductor Quantum Dot Sensitized TiO₂ Film for Photovoltaic Application

“…[18] Extensive studies have been performed to investigate interfacial charge transfer processes, in particular EI [19,20] and ICR [21] between a QD and TiO2 using transient absorption spectroscopy (TAS). The dynamics results confirm that the EI occurs on ultrafast time scales (typically on subpicosecond to 100 ps), [20,[22][23][24][25] while ICR occurs on nanosecond to microsecond time scale. [23,26,27] However, despite these ample kinetic results and investigation to control the interfacial charge transfer reactions, no study has so far been conducted to correlate the interfacial charge transfer dynamics with the solar cell performance.…”

“…The dynamics results confirm that the EI occurs on ultrafast time scales (typically on subpicosecond to 100 ps), [20,[22][23][24][25] while ICR occurs on nanosecond to microsecond time scale. [23,26,27] However, despite these ample kinetic results and investigation to control the interfacial charge transfer reactions, no study has so far been conducted to correlate the interfacial charge transfer dynamics with the solar cell performance. Therefore, no study was reported to design interfacial structures to optimize QD size and solar cell performance.…”

Investigating the effect of different quantum dots on the absorption spectrum and characteristics of quantum dot sensitized solar cells

“…Quantum dots are the major absorbers of sunlight and excitons are produced after absorbing light using QDs. Photocurrent is formed by the transfer of electrons to the TiO 2 anode [18]. Based on the previously described relationships, we simulated the solar cells with different sensitizers.…”