Semitransparent organic photovoltaics using a near-infrared absorbing cyanine dye

A selective near-infrared absorbing heptamethine cyanine dye (Cy7-P) electron donor was used for the fabrication of bilayer solar cells with the acceptor C60. Using a reflective metal top electrode, solar cell optimization resulted in an external power conversion efficiency (η) of 1.5% for layer thicknesses of ~20 nm for Cy7-P and of ~40 nm for C60, with using either PEDOT:PSS or MoO3 as anode and Alq3 as cathode buffer layers. Highly transparent devices were then fabricated by using silver/Alq3 cathodes. Average visible transmittance (450–670 nm) values of, for example, 67.2% (η=0.7%), 62.1% (η=0.9%) or 50% (η=1%) were obtained for different thickness combinations of silver and Alq3. Optimized solar cells had a maximum transparency of 79.8% at 568 nm. The operational stability under 1 sun illumination was T80=30 h, after which 80% of the initial cell performance was reached.