Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices.

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal inks. For the photoactive absorber layer, colloidal CdTe and CdSe nanocrystals (3-5 nm) are synthesized using an inert hot injection technique and cleaned with precipitations to remove excess starting reagents. Similarly, gold nanocrystals (3-5 nm) are synthesized under ambient conditions and dissolved in organic solvents.

Synthesis and Optical Properties of PbSe Nanorods with Controlled Diameter and Length.

The synthesis of PbSe nanorods with low branching (<1%), high aspect ratios (up to ∼16), and controlled lengths and diameters was demonstrated via the removal of water and oleic acid from the synthesis precursors. It was determined that the proper combination of reaction time and temperature allows for the control of PbSe nanorod length and diameter and therefore control over their electronic states, as probed through absorbance and photoluminescence measurements. Similar to PbSe nanowires, nanorods display higher Stokes shifts than for spherical nanocrystals due to intrananorod diameter fluctuations.

Fully solution processed all inorganic nanocrystal solar cells.

The effects of solution (sol) processed contacts of indium tin oxide (ITO-sol) and gold (Au-sol) on solar cells are tested. When combined with solution processed active layers of CdTe/CdSe, all-inorganic fully solution processed solar cells are produced on non-conductive glass substrates. Under AM 1.

Impact of nanocrystal spray deposition on inorganic solar cells.

Solution-synthesized inorganic cadmium telluride nanocrystals (∼4 nm; 1.45 eV band gap) are attractive elements for the fabrication of thin-film-based low-cost photovoltaic (PV) devices. Their encapsulating organic ligand shell enables them to be easily dissolved in organic solvents, and the resulting solutions can be spray-cast onto indium-tin oxide (ITO)-coated glass under ambient conditions to produce photoactive thin films of CdTe.

Control of PbSe nanorod aspect ratio by limiting phosphine hydrolysis.

The aspect ratio and yield of PbSe nanorods synthesized by the reaction of Pb-oleate with tris(diethylamino)phosphine selenide are highly sensitive to the presence of water, making it critical to control the amount of water present in the reaction. By carefully drying the reaction precursors and then intentionally adding water back into the reaction, the nanorod aspect ratio can be controlled from 1.1 to 10 and the yield from 1 to 14% by varying the water concentration from 0 to 204 mM.

Inorganic photovoltaic devices fabricated using nanocrystal spray deposition.

Soluble inorganic nanocrystals offer a potential route to the fabrication of all-inorganic devices using solution deposition techniques. Spray processing offers several advantages over the more common spin- and dip-coating procedures, including reduced material loss during fabrication, higher sample throughput, and deposition over a larger area. The primary difference observed, however, is an overall increase in the film roughness.

Enhanced open-circuit voltage of PbS nanocrystal quantum dot solar cells.

Nanocrystal quantum dots (QD) show great promise toward improving solar cell efficiencies through the use of quantum confinement to tune absorbance across the solar spectrum and enable multi-exciton generation. Despite this remarkable potential for high photocurrent generation, the achievable open-circuit voltage (Voc) is fundamentally limited due to non-radiative recombination processes in QD solar cells. Here we report the highest open-circuit voltages to date for colloidal QD based solar cells under one sun illumination.

The Complex Interaction of Spectroscopic Shifts and Electronic Properties in Semiconductor Nanocrystal Films.

Absorption spectroscopy has traditionally served as a powerful technique for the study of solution synthesized semiconductor nanocrystals, enabling information on the size, dispersity, concentration, and overall quality of a sample to be obtained quickly and easily. When thin, densely packed films of these materials are produced through ligand exchange, spectroscopic shifts to both higher and lower energy are observed. Reduction of the internanocrystal distance can result in both a change to the overall dielectric constant of the film as well as increased electronic coupling, producing a redshift.

Enhanced multiple exciton generation in quasi-one-dimensional semiconductors.

The creation of a single electron-hole pair (i.e., exciton) per incident photon is a fundamental limitation for current optoelectronic devices including photodetectors and photovoltaic cells.

Fluorine-labeling as a diagnostic for thiol-ligand and gold nanocluster self-assembly.

An omega-fluorine-labeled oxyethylene thiol ligand, F(CH2CH2O)2CH2CH2SH, was synthesized, characterized and incorporated into mixed self-assembled monolayers with CH3(OCH2CH2)3SH onto a planar gold substrate and onto 2 nm gold nanoclusters. The fluorine-labeled nanocluster was self-assembled onto gold substrates using alkane dithiol (HS(CH2)nSH; n = 5, 8, 11) and oxyethylene dithiol (HS(CH2CH2O)nCH2CH2SH; n = 1, 2, 3) linking agents with equivalent chain lengths for comparative purposes. X-ray photoelectron spectroscopy (XPS) was used to track the fluorine-label in the self-assembly operations and to evaluate the effectiveness of the dithiols.

Self-assembly of trioxyethylene-encapsulated gold nanoclusters under aqueous conditions.

The aqueous self-assembly of methyl-terminated tri(oxyethylene)thiol-encapsulated gold nanoclusters of varying core size is demonstrated on micrometer scale Au/SiO2 interdigital electrodes. This self-assembly process consists of alternate exposures of the substrate to solutions of either an alpha,omega-dithiol or the gold nanoclusters, resulting in the deposition of these materials onto the electrode surface. A comparison of the procedure in both H2O and CHCl3 solvents shows that the assembly, as monitored by the electrical conductivity of the device, occurs more rapidly in the H2O system.

Ion-induced discrete charging of immobilized water-soluble gold nanoclusters.

Hydrophilic gold nanoclusters were immobilized onto monolayer-modified gold electrodes and PF6-(-)induced rectification and stepwise capacitance charging was studied in aqueous supporting electrolyte by cyclic voltammetry and ac voltammetry.