Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has the merits of high electrical conductivity and solution processability, and can be dispersed in water. To improve the stretchability of PEDOT:PSS-based transparent electrode films, the intrinsically conducting polymer PEDOT:PSS was blended with highly stretchable nonionic waterborne polyurethane (WPU) and coated on a thermoplastic polyurethane (TPU) film. Nonionic WPU has good compatibility with PEDOT:PSS, without affecting the acidity. WPU undergoes hydrogen bonding and coulombic attractions with PEDOT:PSS. With variation of the WPU content, differences in the electrical properties, such as the sheet resistance and mechanical stretchability, of the coated thin films were observed. The film with 2.0 wt% WPU could be stretched to 400% of the electrode surface without damage to the surface of the electrode films. The WPU and TPU films both have a polyester group, which provides good adhesion between the WPU-based transparent electrodes and the TPU substrate films. A stretchable alternating current electroluminescence (ACEL) device was constructed by using the water-based PEDOT:PSS/nonionic WPU composite as both the bottom and top transparent electrodes. The fabricated ACEL remained its initial luminance in the 500% stretched state.

Flexibility and stretchability of solar cells are crucial factors for enhancing their real-life application for wearable devices. Although poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) has been conventionally employed as a hole extraction layer (HEL) in flexible organic or perovskite solar cells, the inherent stretchability of PEDOT:PSS has yet to be convinced. Here, we report a highly stretchable and mechanically stable PEDOT:PSS-based thin film and its application on flexible perovskite solar cells. We synthesized a chemically linked copolymer, P­(SS-co-TFPMA), consisting of PSS and tetrafluoropropyl methacrylate (TFPMA) followed by graft copolymerization with poly­(ethylene glycol) methyl ether methacrylate (PEGMA) to form a P­(SS-co-TFPMA)-g-PEGMA dopant for the PEDOT HEL. The PEDOT:P­(SS-co-TFPMA)-g-PEGMA (PEDOT:PTP) copolymer solution has excellent homogeneity and high phase stability, and its developed HEL film exhibits outstanding stretching capability. After stretching of 300%, PEDOT:PTP films sustain conductivity of over 80% of their original conductivity, whereas the conventional PEDOT:PSS films completely lose their conductivity after a strain of 300%. In addition, the PEDOT:PTP-incorporated flexible perovskite solar cells exhibited improved mechanical stability compared with the unassisted cells, retaining 92% of the initial power conversion efficiency after 1500 bending cycles at a 7 mm radius.