Inkjet printed chalcopyrite CuIn x Ga 1  x Se 2 thin film solar cells Wei Wang, Yu-Wei Su, Chih-hung Chang n Oregon State University, School of Chemical, Biological and Environmental Engineering, 103 Gleeson Hall, Corvallis, OR 97331, USA article info Article history: Received 9 October 2010 Received in revised form 13 April 2011 Accepted 5 May 2011 Available online 31 May 2011 Keywords: Photovoltaic devices Inkjet printing Solar cells Thin films CIGS Solution processing abstract In this paper, we report a novel approach for the fabrication of chalcopyrite CuIn x Ga 1x Se 2 thin film solar cells by inkjet printing. The short circuit current (J sc ), open circuit voltage (V oc ), fill factor (FF), and total area power conversion efficiency (Z) of the device are 29.78 mA/cm 2 , 386 mV, 0.44%, and 5.04%, respectively. Inkjet printing at atmospheric environment offers an opportunity for the direct patterning of absorber materials at large scale. This provides a potential cost advantage over conventional fabrication process that involves sequential deposition, patterning, and etching of selected materials. In addition, inkjet printing increases the raw material utilization ratio compared to more wasteful vacuum-based deposition techniques. & 2011 Elsevier B.V. All rights reserved. 1. Introduction Currently chalcopyrite Cu(In,Ga)(S,Se) 2 (CIGS) thin film solar cells have reached up to 20.1% power conversion efficiency using a three-stage co-evaporation process [1]. Decent conversion efficiency and high chemical stability of CIGS make it a promising p-type material for thin film solar cells. However, the high cost of vacuum-based fabrication process becomes a barrier to affordable commercial modules for the substitution of conventional fossil fuels as a primary energy source. An efficient non-vacuum printing process has the potential to overcome this barrier. Several solution methods have already been reported in the recent years. Liu et al. [2] utilized hydrazine to dissolve binary chalcogenides and deposit CIGS films by spin coating with a high efficiency of 12.2%. The toxic and explosive nature of hydrazine might limit the large scale industrial implementation of this exciting approach. Guo et al. [3] and Akhavan et al. [4] synthe- sized CIGS nanoparticles and fabricated solar cells by drop casting with power conversion efficiencies of 6.23% and 3.1%, respec- tively. A scalable and high throughput synthesis process is needed to lower down the cost of these nanocrystal inks. More recently, Weil et al. [5] demonstrated an air-stable vulcanized ink for the production of large-grained CuInS 2 absorber layers by rolling printing process with a post-KCN etching. A power conversion efficiency of 2.15% was achieved. Solution-based direct printing of inorganic materials offers the possibility of depositing high quality thin films at low temperature under atmospheric conditions, and the direct additive patterning processes that enable the fabrication of high-performance and ultra-low-cost electronics [6–11]. Inkjet printing of inorganic materials is relatively more challenging compared to the inkjet printing of organic materials, especially for semiconductor mate- rials. The first example of printing inorganic semiconducting materials was reported by Ridley et al. [7], who fabricated a thin film transistor by casting CdSe thin films from a precursor solution of cadmium selenide nanocrystals using a micro-pipette. Shimoda et al. [8] fabricated TFTs using inkjetted poly-silicon channel layer. This process, however, requires a special precursor and very stringent control of the oxygen level ( o0.5 ppm) in a dry box in addition to laser re-crystallization and thermal annealing (540 1C). Lee et al. [9] have developed a process that uses metal salt precursors dissolved in an aprotic solvent (i.e. acetonitrile) and is capable of forming uniform and continuous thin films through both digital fabrication (e.g. inkjet printing) and blanket coating (e.g. spin coating) techniques. This feature makes the printing process follow a simple dissolution and drying mechanism. In addition, the high volatility of solvent helps convert the printed liquid thin films to solid metal salt thin films in a short time. The inkjet printed metal salt thin films were converted to oxide semiconductors through a substitution reaction between the metal halide and oxygen (i.e. H 2 O). This synthetic pathway opens a general route to fabricate a variety of patterned metal oxide semiconductors through a simple and low-cost process in an atmospheric environment [9]. This paper reports an exten- sion of this approach to enable inkjet printing of chalcogenide semiconductors. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/solmat Solar Energy Materials & Solar Cells 0927-0248/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2011.05.011 n Corresponding author. Tel.: þ1 541 737 8548; fax: þ1 541 737 4600. E-mail addresses: changch@che.orst.edu, chih-hung.chang@oregonstate.edu (C.-h. Chang). Solar Energy Materials & Solar Cells 95 (2011) 2616–2620