Enhanced Electron Lifetime of CdSe/CdS Quantum Dot (QD) Sensitized Solar Cells Using ZnSe Core–Shell Structure with Efficient Regeneration of Quantum Dots

Abstract

. (2015). Enhanced electron lifetime of CdSe/CdS quantum dot (QD) sensitized solar cells using ZnSe core-shell structure with efficient regeneration of quantum dots. The Journal of Physical Chemistry C: Energy Conversion and Storage, Optical and Electronic Devices, Interfaces, Nanomaterials, and Hard Matter, 119 (5), 2297-2307. Enhanced electron lifetime of CdSe/CdS quantum dot (QD) sensitized solar cells using ZnSe core-shell structure with efficient regeneration of quantum dots AbstractResearch on development of efficient passivation materials for high performance and stable quantum dot sensitized solar cells (QDSCs) is highly important. While ZnS is one of the most widely used passivation material in QDSCs, an alternative material based on ZnSe which was deposited on CdS/CdSe/TiO 2 photoanode to form a semi-core/shell structure has been found to be more efficient in terms of reducing electron recombination in QDSCs in this work. It has been found that the solar cell efficiency was improved from 1.86% for ZnSe0 (without coating) to 3.99% using 2 layers of ZnSe coating (ZnSe2) deposited by successive ionic layer adsorption and reaction (SILAR) method. The short circuit current density (J sc ) increased nearly 1-fold (from 7.25 mA/cm 2 to13.4 mA/cm 2 ), and the open circuit voltage (V oc ) was enhanced by 100 mV using ZnSe2 passivation layer compared to ZnSe0. Studies on the light harvesting efficiency (η LHE ) and the absorbed photon-to-current conversion efficiency (APCE) have revealed that the ZnSe coating layer caused the enhanced η LHE at wavelength beyond 500 nm and a significant increase of the APCE over the spectrum 400-550 nm. A nearly 100% APCE was obtained with ZnSe2, indicating the excellent charge injection and collection process in the device. The investigation on charge transport and recombination of the device has indicated that the enhanced electron collection efficiency and reduced electron recombination should be responsible for the improved J sc and V oc of the QDSCs. The effective electron lifetime of the device with ZnSe2 was nearly 6 times higher than ZnSe0 while the electron diffusion coefficient was largely unaffected by the coating. Study on the regeneration of QDs after photoinduced excitation has indicated that the hole transport from QDs to the reduced species (S 2-) in electrolyte was very efficient even when the QDs were coated with a thick ZnSe shell (three layers). For comparison, ZnS coated CdS/CdSe sensitized solar cell with optimum shell thickness was also fabricated, which generated a lower energy conversion efficiency (η = 3.43%) than the ZnSe based QDSC counterpart due to a lower V oc and FF. This study suggests that ZnSe may be a more efficient passivation layer than ZnS, which is attributed to the type II energy band alignment of the core (CdS/CdSe quantum dots) and passivation shell (ZnSe) structure, leading to more efficient electron-hole separation and slower electron recombination. ABSTRACTResearch on development of efficient passivation materials for high perfor...

Doubling the power conversion efficiency in CdS/CdSe quantum dot sensitized solar cells with a ZnSe passivation layer

“…ZnSe is a good candidate, in view of its E cb and E vb are higher than those of CdS/CdSe QDs; such band alignment would not only prevent the electron back transfer to the electrolyte but may also facilitate the desired hole transport from the QDs to the electrolyte. Udit et al [44] Although ZnSe as a passivation layer has a favorable electronic configuration and has demonstrated effects on improving the power conversion efficiency in QDSSCs, the efficiency remains lower than 5% at present [45,47,48]. In this work, we demonstrated the effects of ZnSe passivation layer with approporiate coverage and thickness on the photovoltaic performance of TiO 2 /CdS/CdSe QDSSCs in terms of light absorption, charge transport, and charge recombination.…”

Effect of defects in TiO2 nanotube thin film on the photovoltaic properties of quantum dot-sensitized solar cells

“…ACCEPTED MANUSCRIPT 13 In this work, a maximum photovoltaic conversion efficiency of 3.1% was achieved for the CdSe QD-sensitized NT-TiO 2 solar cells prepared at 10C. …”

“…Fundamental studies are needed to shed light on the physics and chemistry governing the poor initial performance of QDSSCs when compared to dye-sensitized solar cells (DSSCs). To improve the present QDSSC performance, there are several approaches: (1) enhance the QD loading onto the TiO 2 surface, (2) passivate the surfaces of the QDs and the TiO 2 to reduce excited carrier recombination [13], and (3) develop novel electrolytes and counter electrodes for QDSSCs [14].…”

Graphitic porous carbon derived from human hair as ‘green’ counter electrode in quantum dot sensitized solar cells

“…Figure 4b shows the Bode plots of QDSCs based on different GPC CEs. The information about electron lifetime, τ, in a working device can be obtained from the position of low frequency peak (f) in a Bode plot using the following equation [40]:…”