Publication date: 1st April 2013
Although quantum dot sensitized solar cells (QDSSCs) are very promising devices in the field of solar energy conversion[1], there still are open issues limiting the systematic fabrication of performant devices. Among them, the lack of reproducible, stable and efficient counter electrodes (CEs) is particularly troublesome.
Herein, we present the preparation of copper sulphide CEs by spray deposition to be applied as cathodes in QDSSCs. Spray deposition of Cu(NO3)2 x 3 H2O and CS(NH2)2 resulted in homogeneous amorphous nanosized thin film and subsequent reaction with polysulfide electrolyte delivers Cu2S hierarchical structures, suitable to be applied as CEs. Proposed procedure is very fast as compared with currently adopted strategies (such for instance treatment of brass foils/wires), straightforward, being able to produce several CEs at once, and highly reproducible.
Cu2S hierarchical CEs were applied as cathodes in QDSSCs, whose sensitization layer consisted of SILAR-deposited semiconductor quantum dots, in particular CdS, PbS, CdS/PbS, CdS/CdSe, PbS/CdS/CdSe [2],[3].
For each applied sensitization system, excellent performances were recorded, especially related to improved photocurrent densities (higher than 15 mA/cm2) and fill factors, this latter testifying the good catalytic activity of the spray-deposited CE.
Photoconversion efficiencies as high as 2.98% and 3.75%, with associated incident photo-to-current efficiencies of 80% and 90%, were obtained with mixed networks of PbS/CdS and CdS/CdSe, respectively.
Figure 1. (a) Scheme of band alignment of the different components the QDSC. PbS QD bands are qualitatively illustrated according to nanocrystal sizes. (b) IPCE of selected cells for different kinds of QD. (c) and (d) J-V curves of QDSC sensitized with QDs of various compositions under simulated sunlight (AM 1.5 G, 100 mW cm-2). (e) Pictures of different QD sensitized photoanodes used in this work (left to right: CdS 4 cycles; CdS/CdSe 5/3; PbS/CdS 2/5; PbS 6cycles).
[1] Rühle, S.; Shalom, M.; Zaban, A. Quantum-Dot-Sensitized Solar Cells. Chem. Phys. Chem. 2010, 11, 2290-2304. [2] Lee, Y.-L.; Lo, Y.-S. Highly Efficient Quantum-Dot-Sensitized Solar Cell Based on Co-Sensitization of CdS/CdSe. Adv. Func. Mat. 2009, 19, 604-609. [3] Lee, H.; Wang, M.; Chen, P.; Gamelin, D.R.; Zakeeruddin, S.M.; Gratzel, M.; Nazeeruddin Md K., Efficient CdSe Quantum Dot-Sensitized Solar Cells Prepared by an Improved Successive Ionic Layer Adsorption and Reaction Process. Nano Lett. 2009, 9, 4221-4227.
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