HOPV12 - Blogs

4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 111
C11 - Copper indium gallium diselenide hybrid solar cells comprising solutiondeposited
window and organic buffer layers
Manuel Reinhard, Johannes Kuhn, Christoph Simon, Alexander Colsmann, Uli Lemmer
Karlsruhe Institute of Technology, Light Technology Institute, Engesserstr. 13, Karlsruhe, 76131, DE
Thin-film chalcopyrite solar cells based on copper indium gallium diselenide (CIGS) exhibit
record power conversion efficiencies of more than 20%. In order to compete with the
predominant silicon based devices it is key to further reduce the cost per watt and hence
explore new device and fabrication concepts for cheaper production processes. In this study,
we present solution-processable, non-toxic and potentially printable organic semiconductors
as a replacement for the commonly used cadmium sulfide (CdS) buffer layer. In particular,
organic semiconductors with LUMO energies above 3eV allow for the fabrication of efficient
hybrid solar cells.
By performing bias dependent impedance spectroscopy we can show that these organic
semiconductors reduce the recombination at the CIGS interface and enhance the minority
carrier lifetimes as compared to buffer-free devices.
Furthermore, we find a relation between the open circuit voltage (VOC) of the devices and
the position of the N2 defect level within the absorber bulk as identified by temperaturedependent
admittance spectroscopy. The higher the VOC of the photovoltaic device the further
this defect level approaches the valence band of CIGS indicating a reduced Shockley-Read-Hall
recombination rate. We further replace the commonly used transparent zinc oxide top
electrode with a solution-processable highly conductive mesh electrode comprising
commercially available silver nanowires. These electrodes exhibit a transmittance of more
than 80% in the visible range and sheet resistances of less than 20Ω/□, hence allowing for the
fabrication of 5% efficient solar cells.
© SEFIN 2012