Flexible ITO-free organic photovoltaics on ultra-thin flexible glass substrates with high efficiency and improved stability

The ability for organic solar cells to be conformable and bendable enables them to be used in a broad range of applications. Indium tin oxide (ITO) or PEDOT:PSS on plastic substrates such as poly(ethylene terephthalate) or poly(ethylene napthalate) (PET or PEN) have been used for transparent conductive electrodes (TCEs) for flexible devices. However, ITO is brittle and when used on flexible substrates is prone to cracking, and the acidity of PEDOT:PSS can lead to corrosion of the ester-based plastic substrates and cause device degradation. In this work, TCEs based on modified high-conductivity PEDOT:PSS on 100 μm-thick flexible glass substrates are used as the anode for organic solar cells. The optimized PEDOT:PSS TCE anode on flexible glass has a sheet resistance of ≈30 Ω/sq and a transmission of ≈77% at 550 nm, with a broad transmission window between 300 and 800 nm. The best PEDOT:PSS on flexible glass-based organic solar cell has a power conversion efficiency (PCE) of 8.0%, which is higher than devices comprising ITO or PEDOT:PSS on PEN, which have PCEs of 6.4% and 5.8%, respectively. It is also found that the ultra-thin glass devices can be scaled, with 1.6 cm ² flexible cells having an efficiency of 5.2%.