Simple fabrication of highly conductive and passivated PEDOT:PSS film via cryo-controlled quasi-congealing spin-coating for flexible perovskite solar cells

To significantly increase the applicability of inverted-planar flexible perovskite solar cells (PSCs), the achievement of high electrical conductivity, excellent moisture resistance and reproducibility of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layer with simple fabrication (low cost and ease of mass manufacture) during spin-coating are goals pursued by researchers. Herein, for the first time, we propose a facile strategy of cryo-controlled quasi-congealing spin-coating to improve the PEDOT:PSS quality to a new extent. The congealed surface and strengthened hydrogen-bonds between solvent and PSS chains can effectively suppress the moisture corrosion during spin-coating. In addition, the electrical conductivity of PEDOT:PSS can be further enhanced owing to the uniformity of PEDOT:PSS grains and greater co-solvent effect facilitated by induced Young’s modulus during spin-coating. The considerably smooth and uniform film with improved conductivity can be achieved even as fabricating under high humidity environment. Furthermore, this smooth and passivated PEDOT:PSS can facilitate high crystalline perovskite and better interfacial contact between them, which not only enhance the efficiency, but also greatly improve repeated mechanical deformation stability of PSCs. As a result, the power conversion efficiency (PCE) of rigid and flexible PSCs can be improved to 17.65% and 15.13%, respectively. Both devices show about 14% enhancement in PCE compared to conventional one.