Transparent Metal Network with Low Haze and High Figure of Merit applied to Front and Back Electrodes in Semitransparent ITO-free Polymer Solar Cells

In the quest for indium-tin oxide (ITO)-free photovoltaics and for building integrated as well as automobile roof applications, novel transparent electrodes for both front and back electrodes are required. Here we report the fabrication and integration of submicrometer transparent silver (Ag) and gold (Au) metal network electrodes, which are invisible to the naked eye, in organic photovoltaic devices. We exploit the idea of using the spontaneous cracking of a polymer layer as template to prepare the metal network. The main challenge is to apply the cracked template approach on top of soluble organic layers and to lift off the template without damaging the photoactive layer. We demonstrate that Ag or Au back electrodes can be fabricated maintaining a transmittance of 80% for the whole visible range. These electrodes exhibit ultralow haze of approximately 5% and an excellent figure of merit value. Moreover, the ITO-free semitransparent polymer solar cell incorporating the Ag/Ag network electrodes exhibits 57% transmittance above 650 nm.