[Paper] Effects of Self-Assembled Monolayers on Solid- State CdS Quantum Dot Sensitized Solar Cells




Effects of Self-Assembled Monolayers on Solid- State CdS Quantum Dot Sensitized Solar Cells, Pendar Ardalan, Thomas P. Brennan, Han-Bo-Ram Lee, Jonathan R. Bakke, I-Kang Ding, Michael D. McGehee, Stacey F. Bent, ACS Nano, 2011


http://dx.doi.org/10.1021/nn103371v 


Abstract


Quantum dot sensitized solar cells (QDSSCs) are of interest for solar energy conversion because of their tunable band gap and promise of stable, low-cost performance. We have investigated the effects of self-assembled monolayers (SAMs) with phosphonic acid head groups on the bonding and performance of cadmium sulfide (CdS) solid-state QDSSCs. CdS quantum dots∼2 to ∼6 nm in diameter were grown on SAM-passivated planar or nanostructured TiO2 surfaces by successive ionic layer adsorption and reaction (SILAR), and photovoltaic devices were fabricated with spiro-OMeTAD as the solid-state hole conductor. X-ray photoelectron spectroscopy, Auger electron spectroscopy, ultraviolet-visible spectroscopy, scanning electron microscopy, transmission electron microscopy, water contact angle measurements, ellipsometry, and electrical measurements were employed to characterize the materials and the resulting device performance. The data indicate that the nature of the SAM tail group does not significantly affect the uptake of CdS quantum dots on TiO2 nor their optical properties, but the presence of the SAM does have a significant effect on the photovoltaic device performance. Interestingly, we observe up to∼3 times higher power conversion efficiencies in devices with a SAM compared to those without the SAM.