Effective Mg:Ag / MoO 3 recombination zone for tandem organic photovoltaic devices
- PDF / 4,615,615 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 6 Downloads / 186 Views
Effective Mg:Ag / MoO3 recombination zone for tandem organic photovoltaic devices A. R. Jeong, S. Wiesner, S. Fengler, M. Ch. Lux-Steiner, M. Rusu* Institut für Heterogene Materialsysteme, Helmholtz-Zentrum Berlin für Materialien und Energie, Lise-Meitner Campus, Hahn-Meitner-Platz 1, 14109 Berlin, Germany ABSTRACT We demonstrate an effective recombination zone consisting of Mg:Ag (1:3) alloy and MoO3 layers with 0.8 nm and 3 nm respectively for application in tandem organic photovoltaic devices based on zinc phthalocyanine (ZnPc) donor and fullerene C60 acceptor. The Mg:Ag layer ensures an optimum electron selectivity, while MoO3 layer effectively selects holes. A conversion efficiency of 2.2% has been achieved under an illumination of 100 mW/cm2 at room temperature. The open circuit voltage of 810 mV is close to the sum of the open circuit voltages of the constituent single cells. The recombination Mg:Ag-MoO3 layer system is investigated with regard to the requirements of high optical transparency, work function compatibility, and facilitation of light absorption. The respective characterizations were carried out by UV-Visible spectroscopy, Kelvin probe force microscopy in ultrahigh vacuum, current-voltage and external quantum efficiency methods. INTRODUCTION Organic photovoltaics (OPV) have attracted much attention due to potential light-weight, low cost, transparency and flexible alternative to conventional inorganic solar cells. However, the absorber thickness in single solar cells is constrained by the exciton diffusion length which is much smaller than the light absorption length [1,2]. Therefore, maximum theoretical efficiencies are difficult to achieve on single photovoltaic devices. Tandem solar cells, which consist of two or more single cells with complimentary absorptions, have been considered as an effective approach to overcome this limitation. For the configuration of tandem solar cells, series connected architectures have been widely used. Tandem devices have already achieved high efficiencies of 12%, which means that tandem organic photovoltaic cells are promising candidates for commercial applications [3]. In these architectures, utilization of effective recombination zones for the realization of the series connection between the sub-cells is one of the key aspects to achieve high-efficient tandem devices. In this work, we demonstrate an efficient recombination zone with ultra-thin Mg:Ag (1:3) and MoO3, which was reported as electron transport [4,5] and hole transport layers [6-9], respectively. The recombination zone indicates high transparency, proper band alignment between front and back cells, and adequate photoresponse within zinc phthalocyanine (ZnPc) and C60 regions. EXPERIMENT The OPV devices were prepared with ZnPc and C60 by organic vapor phase deposition (OVPD) [10]. The organic layers were deposited on cleaned indium tin oxide (ITO) substrates coated by poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) layers
prepared by spin-coating. The recombination zone was pre
Data Loading...
