Towards large-scale production of solution-processed organic tandem modules based on ternary composites: Design of the intermediate layer, device optimization and laser based module processing Ning Li a,n , Peter Kubis a,d , Karen Forberich a , Tayebeh Ameri a , Frederik C. Krebs b , Christoph J. Brabec a,c a Institute of Materials for Electronics and Energy Technology (I-MEET), Friedrich-Alexander-University Erlangen-Nuremberg, Martensstraße 7, 91058 Erlangen, Germany b Department of Energy Conversion and Storage, Technical University of Denmark, Frederiksborgvej 399, DK-4000 Roskilde, Denmark c Bavarian Center for Applied Energy Research (ZAE Bayern), Haberstraße 2a, 91058 Erlangen, Germany d Erlangen Graduate School in Advanced Optical Technologies (SAOT), Paul-Gordan-Straße 6, 91052 Erlangen, Germany article info Available online 2 October 2013 Keywords: Solution processing Organic tandem solar cells Intermediate layer Ternary composites Optical-simulation Laser-based module processing abstract We report on a novel approach including: 1. the design of an efficient intermediate layer, which facilitates the use of most high performance active materials in tandem structure and the compatibility of the tandem concept with large-scale production; 2. the concept of ternary composites based on commer- cially available materials, which enhances the absorption of poly(3-hexylthiophene) (P3HT) and as a result increase the PCE of the P3HT-based large-scale OPV devices; 3. laser-based module processing, which provides an excellent processing resolution and as a result can bring the power conversion efficiency (PCE) of mass-produced organic photovoltaic (OPV) devices close to the highest PCE values achieved for lab-scale solar cells through a significant increase in the geometrical fill factor. We believe that the combination of the above mentioned concepts provides a clear roadmap to push OPV towards large-scale production and commercial applications. & 2013 Elsevier B.V. All rights reserved. 1. Introduction In the last decade organic photovoltaic (OPV) has attracted more and more attention in the research community owing to its remarkable advantages compared to conventional photovoltaics, such as low cost, light weight and easy large-scale production [1– 4]. The power conversion efficiency (PCE) of lab-scale OPV devices has reached  8–10% [5–8] by the development of novel donor materials and meticulous device optimization, indicating a bright future for OPV devices in commercial applications. As the most studied active material, poly(3-hexylthiophene): phenyl-C 61 -butyric acid methyl ester (P3HT:[60]PCBM) is one of the most promising candidates until now for large-scale pro- duction because of the commercial availability, low cost and easy processing in air. However, the P3HT:[60]PCBM-based OPV devices give an averaged PCE of  3% for the lab-scale solar cells [9] and of  2% for the mass-produced OPV devices [10]. The PCE of P3HT:PCBM-based OPV devices is limited by the narrow absorption of P3HT, which results in a decreased short circuit current (J sc ), and thermalization losses, which result in a decreased open circuit voltage (V oc ). Obviously, compared to the 410% PCE reported for the lab-scale solar cells [8] the PCE of mass-produced OPV devices is still at an initial stage, which is mainly due to the lack of commercially available high perfor- mance active materials and non-optimized processing techni- ques with a low degree of control. The tandem concept, which involves stacking two or more cells with complementary absorption spectra in serial or parallel connection [11,12], has been proven to simultaneously address both loss-mechanisms of OPV devices: the narrow absorption window and the thermallization losses. Recently, the PCE of lab- scale OPV devices has surpassed the 12% milestone by using the tandem concept (press release by Heliatek), which has the potential to boost the PCE of OPV devices towards the expected efficiency of 15% [13], while the PCE of mass-production com- patible single-junction devices is restricted to 10–11% [14]. The intermediate layer (IML) consisting of a hole- and an electron- transporting layer is considered to lie at the heart of the tandem structure. The holes and electrons that are selectively collected by the IML should recombine efficiently at its interface [12]. Increasing the PCE of tandem devices toward 15% theoretical efficiency requires the design of efficient and reliable IMLs. We Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/solmat Solar Energy Materials & Solar Cells 0927-0248/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.solmat.2013.09.003 n Corresponding author. Tel.: þ49 9131 85 27634; fax: þ49 9131 85 28495. E-mail address: Ning.Li@ww.uni-erlangen.de (N. Li). Solar Energy Materials & Solar Cells 120 (2014) 701–708