How Important is Working with an Ordered Electrode to Improve the Charge Collection Efficiency in Nanostructured Solar Cells?

Abstract

The collection efficiency of carriers in solar cells based on nanostructured electrodes is determined for different degrees or morphological one-dimensional order. The transport process is modeled by random walk numerical simulation in a mesoporous electrode that resembles the morphology of nanostructured TiO2 electrodes typically used in dye-sensitized solar cells and related systems. By applying an energy relaxation procedure in the presence of an external potential, a preferential direction is induced in the system. It is found that the partially ordered electrode can almost double the collection efficiency with respect to the disordered electrode. However, this improvement depends strongly on the probability of recombination. For too rapid or too slow recombination, working with partially ordered electrodes will not be beneficial. The computational method utilized here makes it possible to relate the charge collection efficiency with morphology. The collection efficiency is found to reach very rapidly a saturation value, meaning that, in the region of interest, a slight degree of ordering might be sufficient to induce a large improvement in collection efficiency.

Charge collection properties of dye-sensitized solar cells based on 1-dimensional TiO2 porous nanostructures and ionic-liquid electrolytes

“…Furthermore, the reduction of the recombination losses and the columnar morphology is especially interesting for novel electrolytes based on cobalt-complexes [7,75], which present strong recombination and diffusion limitations. As shown recently [36,76], using a 1D morphology is only interesting for architectures where recombination is strong. This is case in the systems studied in this work, where an ionic-liquid electrolyte is utilized.…”

“…Furthermore, although not mentioned very often, these electrolytes show a strong tendency to accelerate recombination [34,35]. The importance of using 1-D nanostructures when the electrolyte introduces a limitation in recombination has been demonstrated recently [36].…”

Metal oxide mesocrystals with tailored structures and properties for energy conversion and storage applications

“…78 In addition, transient photocurrent measurements and random walk numerical simulations have shown that the ordering of a nanocrystalline structure significantly influences charge transport and recombination, which are closely related to the performance of photovoltaic cells. 82,83 Zaban and co-workers 82 found that the highest degree of ordering in porous TiO 2 nanocrystalline films correlates with the highest values of effective diffusion coefficient. Indeed, MCs consisting of NCs highly oriented in the same direction are an ideal system to study this issue.…”

“…75,76 It has been suggested that the dense packing of TiO 2 nanocrystals (NCs) enhances the photocatalytic activity and performance of dyesensitized solar cells owing to the efficient interparticle electron transfer between NCs. [77][78][79][80][81][82][83] For example, the Choi group reported that mesoporous TiO 2 consisting of compactly packed nanoparticles showed higher photocatalytic activity for H 2 evolution than that shown by colloidal and commercial TiO 2 samples in both UV and visible light (dye-sensitized) systems. 78 In addition, transient photocurrent measurements and random walk numerical simulations have shown that the ordering of a nanocrystalline structure significantly influences charge transport and recombination, which are closely related to the performance of photovoltaic cells.…”

Physical Modeling of Photoelectrochemical Hydrogen Production Devices

“…The exact origin and location of the traps is still debated and several different theories have been proposed 101 54,104 . If the charge transport is efficient to begin with, there is almost no room for improvements, and when the charge transport properties are poor, the improvements in the electrode structure are not enough to compensate for the shortcomings in the material properties 54,104 .…”