Journal of the Korean Physical Society, Vol. 61, No. 9, November 2012, pp. 1494∼1499 Fabrication and Characteristics of Fully-sprayed ZnO/CdS/CuInS 2 Solar Cells Tran Thanh Thai, ∗ Nguyen Duc Hieu, Luu Thi Lan Anh, Pham Phi Hung and Vo Thach Son School of Engineering Physics, Hanoi University of Science and Technology, Hanoi 84-04, Vietnam Vu Thi Bich Center for Quantum Electronics, Institute of Physics, Vietnam Academy of Science and Technology (VAST), Hanoi 84-04, Vietnam (Received 2 December 2011, in final form 23 June 2012) This paper reports the successful fabrication of glass/ZnO/CdS/CuInS2 solar cells with a su- perstrate structure deposited using full spray pyrolysis deposition (FSPD). The structure, and the optical and electrical properties of the constituent layers are investigated. The CuInS2 (CIS) film deposited from a starting solution with [Cu]/[In] = 1.1 and the Al-doped CuInS2 (CIAS) film de- posited from a solution with [Cu]/[In] = 1.0 and [Al]/[In] = 0.12, and using a sulfurization process, is observed to exhibit the best crystallites with tetragonal structures. The optical band-gap of the CIAS film is obtained as 1.49 eV. Moreover, physical properties of both the ZnO and the CdS thin films are also studied. The obtained parameters of the cells are an open-circuit voltage of VOC = 425 mV, a short circuit current density of JSC = 14.02 mA/cm 2 , a fill factor of FF = 28.75%, and a conversion efficiency of η = 1.71%. The results in our experiment show that FSPD is a potential technique for preparing solar cells based on CIS absorbers in a superstrate structure with low cost and high performance. PACS numbers: 81.15.Rs, 79.60.Dp, 85.60.Bt Keywords: Solar cells, CuInS 2 , Ultrasonic spray pyrolysis DOI: 10.3938/jkps.61.1494 I. INTRODUCTION Cu-chalcopyrite semiconductor materials have emer- ged for decades as promising candidates for absorber lay- ers in heterojunction solar cells [1–5]. Recently, a high conversion efficiency of 20.3% has been achieved with CuInSe 2 (CISe) solar cells [3]. However, these CISe tech- nologies still have some problems. They include the ad- justment of stoichiometry, and the use of other elements (Ga, Na, S) at increased production costs in order to achieve high efficiencies [1]. Moreover, the presence of selenium and the steps of selenization are also problem- atic from an environmental view due to the potential toxicity [1,4]. For these reasons, today, solar cells based on a CuInS 2 (CIS) absorption layer have attracted much attention from research groups [1,2,4,5]. CIS has sev- eral advantages with respect to other chalcopyrite-based materials. First of all, the bandgap of 1.53 eV is ideal for optimal absorption of solar radiation. Second, unlike CISe or CIGSe, it does not contain the poisonous ele- ment Se. Third, CIS as an absorber layer material for thin-film solar cells has the highest theoretical conver- sion efficiency of 30.5% among Cu-chalcopyrite absorber * E-mail: thaittdhqn@gmail.com; Fax: +84-4-3869-3498 materials [1,2,4,5]. In the case of CIS absorber-layer-based substrate- structure solar cells, the most successful techniques for absorber preparation have been the multi-source- evaporation and the two-step (sulfurization of metal pre- cursor films) processes [1,4,5]. Cells deposited by using vacuum-based techniques have reached a confirmed total area efficiency of 11.4% [4]. However, they were vacuum techniques that had some disadvantages including the high-cost and low-speed [2,5]. Meanwhile, non-vacuum techniques such as ion layer gas reaction spray pyroly- sis and electro-deposition can generate low-cost, high- speed photovoltaic production [2,4,5]. Therefore, non- vacuum techniques have received extensive consideration from research groups concerned with the aim to reduce the production costs. Among these methods, spray py- rolysis supports a superstrate structure design, which is used for full-layer-sprayed solar cells (full spray pyrolysis depostion-FSPD) [2,5]. However, the efficiency of CIS cells deposited by using FSPD is quite low compared with that of CIS cells prepared by using a vacuum-based method. Thus, this deposition method must be devel- oped more in order to enhance the conversion efficiency. In this study, we develop ultrasonic spray pyrolysis (USP) deposition of semiconductor thin films to produce solar cell structures. The USP technique is chosen be- -1494-