Aerosol jet printed grid for ITO-free inverted organic solar cells

Aerosol jet printing is investigated as a new deposition method for a current collecting grid in indium tin oxide (ITO) free organic solar cells with an inverted layer sequence. In this device configuration, the ITO layer which usually serves as the hole contact is replaced by a transparent highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer in combination with a silver grid deposited by aerosol jet printing. Since the cells are illuminated from the grid side, the optimisation of the grid design is a trade-off between area coverage and conductivity of the grid lines. These factors have been controlled by the printing parameters such as chuck temperature, printing speed and the number of printing passes. In this paper, we demonstrate that continuous, conductive grid lines with a minimum line width of 58 mu m can be processed on the top of the PEDOT:PSS layer. For single pass printing the area coverage varied from 5.8% to 11.9% with corresponding effective sheet resistances ranging from 8.9 Omega to 1.5 Omega. The ITO-free inverted devices with aerosol jet printed grid (an active area of 1.1 cm(2)) show comparable performance to the cells with an evaporated gold grid. The effective sheet resistance can be further decreased by multiple printing passes without increasing the area coverage proportionally due to an improved aspect ratio. By increasing the conductivity and aspect ratio by multiple line printing, the cell length in the module structures can be significantly extended. (C) 2012 Elsevier B.V. All rights reserved.