Treatment Effects of ZnO and Al:ZnO Photoanodes on Short-Circuit Photocurrent and Open-Circuit Photovoltage of Quantum Dot Sensitized Solar Cell Using Ag Nanoparticles M. Eskandari a , V. Ahmadi b, * a Department of Nanomaterial Engineering, Tarbiat Modares University, Tehran, Iran b Department of Electrical Engineering, Tarbiat Modares University, Tehran, Iran A R T I C L E I N F O Article history: Received 13 November 2014 Received in revised form 19 February 2015 Accepted 28 February 2015 Available online 3 March 2015 Keywords: Aluminum doped ZnO nanorods quantum dot sensitized solar cells photoanode Ag nanoparticles A B S T R A C T This study investigates the treatment effects of ZnO and Al:ZnO (AZO) photoanodes on short-circuit photocurrent (J sc ) and open-circuit photovoltage (V oc ) of quantum dot sensitized solar cell using Ag nanoparticles (Ag NPs). Current density-voltage (J–V) characterization showed that J sc of QDSSC rises for treated ZnO photoanode with Ag NPs, whereas it decreases in AZO/Ag NPs photoanode based QDSSCs. Also, it was found that V oc raises when treating both ZnO and AZO photoanodes of QDSSCs with Ag NPs. These results were studied using electrochemical impedance spectroscopy (EIS) and absorption spectra. EIS results indicated that recombination resistance of photoanode/electrolyte interfaces of QDSSC increases with decoration of Ag NPs on ZnO and AZO photoanodes which, consequently, results in reduction of electron back into electrolyte. Furthermore, it was observed that chemical capacitance of photoanode enhances with treatment of ZnO photoanode, while being extremely reduced for AZO photoanode. ã 2015 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, numerous studies have been widely conducted on quantum dot sensitized solar cells (QDSSCs). QDSSCs work based on the interfacial charge separation between a short band gap (donor) and a large band gap (acceptor) semiconductor. These solar cells are founded on the semiconductor photoanode, typically TiO 2 or ZnO, decorated by QD sensitizers [1–10]. By controlling the quantum dot (QD) size, these cells can absorb a wide range of solar spectra, resulting in higher efficiency of the cell. In addition, QDs possess higher extinction coefficients leading to desired electron transfer to semiconductor [11]. Electron transfer from QD to semiconductor and electron transport in the semiconductor is an essential property of QDSSCs. Compared to TiO 2 , ZnO involves a higher electronic mobility and diffusion coefficient that causes easier injection of the electrons into the ZnO conduction band (CB) [12]. Moreover, ZnO has several advantages over TiO 2 such as higher thermal stability, easier growth, and lower synthesis cost which makes it an efficient alternative for the TiO 2 [13]. Since pure ZnO possesses poor conductivity, doping it with III, IV, V, and VI group elements is usually necessary to improve its conductivity [14–21]. Presently, conductivity improvement of ZnO nanostruc- tures is performed by doping with gallium [22–24], indium [25], and aluminum [26,27]. In the dye sensitized solar cells (DSSC), short circuit current density (J cs ) is improved from 0.65 mA/cm 2 to about 1.3 mA/cm 2 with doping Al into ZnO nanorods as photo- anode [28]. The improved DSSC performance is attributed to the enhanced electrical conductivity, causing easier transfer of electrons into the ZnO CB. The Al doped ZnO arrays can be used as a novel FTO free photoanode for solar water splitting, resulting in the improved absorbance of solar light and increased cell performance [29]. Besides, using metallic nanoparticles in solar cells facilitates improving the efficiency of the cell performance because of the enhanced optical absorption and scattering spectrum. So far, this approach has been used in different solar cell structures to modify their performance. For instance, using Ag nanoparticles (Ag NPs) in photoanode of dye sensitized solar cell, the short circuit current is increased and cell efficiency is improved from 0.48% to 0.81% [30]. TiO 2 NPs loaded with Au NPs are found to improve the efficiency and short-circuit current density (J sc ) of DSSCs [31]. However, some studies show that metallic nano- particles can result in photocurrent reduction [32]. We investigat- ed the effect of Ag NPs concentration on the cell performance in our previous work [33]. Results showed that J sc enhances with * Corresponding author. Tel. +98 2182883368; fax: +98 2182883368. E-mail address: v_ahmadi@modares.ac.ir (V. Ahmadi). http://dx.doi.org/10.1016/j.electacta.2015.02.239 0013-4686/ ã 2015 Elsevier Ltd. All rights reserved. Electrochimica Acta 165 (2015) 239–246 Contents lists available at ScienceDirect Electrochimica Acta journa l home page : www.e lsevier.com/loca te/ele cta cta