Enhanced Electron Transport in Dye-Sensitized Solar Cells Using Short ZnO Nanotips on A Rough Metal Anode

Abstract

Many efforts have been directed toward the enhancement of electron transport in dye-sensitized solar cells (DSSC) using one-dimensional nanoarchitectured semiconductors. However, the improvement resulting from these ordered 1-D nanostructured electrodes is often offset or diminished by the deterioration in other device parameters intrinsically associated with the use of these 1-D nanostrucutres, such as the two-sided effect of the length of the nanowires impacting the series resistance and roughness factor. In this work, we mitigate this problem by allocating part of the roughness factor to the collecting anode instead of imparting all the roughness factors onto the semiconductor layer attached to the anode. A microscopically rough Zn microtip array is used as an electron-collecting anode on which ZnO nanotips are grown to serve as the semiconductor component of the DSSC. For the same surface roughness factor, our Zn-microtip|ZnO-nanotip DSSC exhibits an enhanced fill factor compared with DSSCs that have ZnO nanowires supported by a planar anode. In addition, the open-circuit voltage of the Zn-microtip|ZnO-nanotip DSSC is also improved due to a favorable band shift at the Zn−ZnO interface, which raises the Fermi level of the semiconductor and consequently enlarges the energy gap between the quasi-Fermi level of ZnO and the redox species. With these improvements, the overall efficiency becomes 1.4% with an open-circuit voltage of 770 mV, while the surface roughness factor of ZnO is approximately 60. Electrochemical impedance spectroscopic study reveals that the electron collection time is much shorter than the electron lifetime, suggesting that fast electron collection occurs in our device due to the significantly reduced electron collection distance along the short ZnO nanotips. The overall improvement demonstrates a new approach to enhance the efficiency of dye-sensitized solar cells.

Review of the Multi-scale Nano-structure Approach to the Development of High Efficiency Solar Cells

“…While the branched growth nanowires and the backbone NW have a monolithic single crystalline relationship to the CVD grown comb-like ZnO nanostructure, the hydrothermally grown secondary branched ZnO NWs did not originate from the backbone NW, but from the ZnO seed nanoparticles in the c axis direction with single crystal wurtzite structure [10]. Other researchers reported similar effects [12][13][14] and very similar approaches to that for ZnO branched nanostructures were demonstrated for TiO 2 [15][16].…”

Photochemical performance of ZnO nanostructures in dye sensitized solar cells

“…Extensive research in this area has been performed on TiO 2 based DSSC exhibiting an overall conversion efficiency of 11.2% [3]. The energy loss due to the recombination of electrons and either the oxidised sensitizers or electron accepting species of the electrolyte during charge transport process has mainly restricted the improvement of conversion efficiency of DSSC based devices [4].…”

Double‐Layer Structure Photoanode with TiO2 Nanotubes and Nanoparticles for Dye‐Sensitized Solar Cells

“…Furthermore, TiO 2 nanoparticles with high specific surface area have been widely used as photoanode in DSSC . However, the high surface area of the nanoparticles also results in the large amount of grain boundaries between nanoparticles, leading to the presence of many electron‐hole recombination centers . A random zigzag walk over the disordered framework of TPs is believed to increase the electron scattering.…”

“…7 However, the high surface area of the nanoparticles also results in the large amount of grain boundaries between nanoparticles, leading to the presence of many electron-hole recombination centers. 8,9 A random zigzag walk over the disordered framework of TPs is believed to increase the electron scattering. Furthermore, the poor absorption of long-range wavelength light of TPs is also a key factor limiting the conversion efficiency.…”