A Quasi-Quantum Well Sensitized Solar Cell with Accelerated Charge Separation and Collection

Abstract

Semiconductor-sensitized solar cell (SSSC) represents a new generation of device aiming to achieve easy fabrication and cost-effective performance. However, the power of the semiconductor sensitizers has not been fully demonstrated in SSSC, making it actually overshadowed by dye-sensitized solar cell (DSSC). At least part of the problem is related to the inefficient charge separation and severe recombination with the current technologies, which calls on rethinking about how to better engineer the semiconductor sensitizer structure in order to enhance the power conversion efficiency (PCE). Herein we report on using for the first time a quasi-quantum well (QW) structure (ZnSe/CdSe/ZnSe) as the sensitizer, which is quasi-epitaxially deposited on ZnO tetrapods. Such a novel photoanode architecture has attained 6.20% PCE, among the highest reported to date for this type of SSSCs. Impedance spectra have revealed that the ZnSe/CdSe/ZnSe QW structure has a transport resistance only a quarter that of, but a recombination resistance twice that of the ZnSe/CdSe heterojunction (HJ) structure, yielding much longer electron diffusion length, consistent with the resulting higher photovoltage, photocurrent, and fill factor. Time-resolved photoluminescence spectroscopy indicates dramatically reduced electron transfer from ZnO to the QW sensitizer, a feature which is conducive to charge separation and collection. This study together with the impedance spectra and intensity modulated photocurrent spectroscopies supports a core/shell two-channel transport mechanism in this type of solar cells and further suggests that the electron transport along sensitizer can be considerably accelerated by the QW structure employed.

Hierarchical ZnO nanorod-on-nanosheet arrays electrodes for efficient CdSe quantum dot-sensitized solar cells

“…Many kinds of metal oxide semiconductors have been employed as photoanode materials for QDSSCs, such as TiO2 [5][6][7][8][9], ZnO [10][11][12][13], SnO2 [14,15], and Zn2SnO4 [16,17]. Among them, ZnO has been considered to be a recommendable alternative to the most competitive TiO2 [5,[18][19][20][21] for its intrinsic electronic and electrochemical advantages, and the highest power conversion efficiency (PCE) record for ZnO based QDSSCs has already been promoted to 6.20% [13]. Two most attractive properties of ZnO are the excellent electron mobility and the anisotropic growth [4,22].…”

“…ZnO has the highest reported electron mobility (200-1000 cm 2 V -1 s -1 ) [4,23] among the various candidates of photoanode materials, which is more than 1 order of magnitude larger than TiO2 (0.1-1.0 cm 2 V -1 s -1 ) [24]. Meanwhile, the ease of crystallization and anisotropic growth of ZnO allows the rich family of ZnO nanostructures, including rods [11,25], tubes [26,27], sheets [28,29], rings [30], hollow spheres [31,32], tetrapods [13], nanourchins [33] and many other hierarchical structures [34][35][36][37][38]. Nanorod (NR) is still the easiest prepared and most commonly used morphology in ZnO photoanode materials.…”

Raman and photoluminescence investigation of CdS/CdSe quantum dots on TiO2 nanoparticles with multi-walled carbon nanotubes and their application in solar cells

“…Quantum dots have been widely used in solar cells to absorb the sunlight for photocurrent generation [1][2][3][4]. Time-resolved second harmonic spectroscopy has been used to demonstrate the efficient hot-electron injection from PbSe nanocrystals to TiO 2 nanoparticles [5].…”

“…The fabrication process of QDs is also easier than that of organic dyes, which brings a benefit to reach the aim of low-cost solar energy. Cascade QDs have been used to increase the power conversion efficiency (PCE) of QDSSCs, using materials such as CdS/CdTe, CdS/CdSe, ZnSe/CdSe, and ZnSe/CdSe/ZnSe [4,[8][9][10]. TiO 2 nanoparticles [11,12] and ZnO nanostructures [1,2,4] have been widely used as photoanodes.…”

A structure of CdS/CuxS quantum dots sensitized solar cells

“…However, the state of art chalcogenide QDs based QDSCs (e.g., CdSe, 8 18 and QDs engineering by absorption extension, element doping, and surface modification. [19][20][21] In nanometer-sized QDs, the surface to interior atom ratio is high. The surface atoms have lower coordination number than the corresponding volume atoms leading to high probability that they act as the electrons or holes traps.…”