Highly efficient and stable flexible perovskite solar cells enabled by using plasma-polymerized-fluorocarbon antireflection layer

Despite of enormous potential in niche applications, flexible perovskite solar cells (F-PSCs) still suffer from low power conversion efficiency (PCE) compared to rigid PSCs largely because of the reduced photocurrent driven by low transmittance of their flexible substrate and transparent electrode. This paper presents a plasma-polymerized-fluorocarbon (PPFC) thin film as an antireflection (AR) coating material for enhancing the efficiency of F-PSCs. The PPFC, which are deposited on flexible polyethylene terephthalate (PET) substrates at low temperature by a mid-range frequency sputtering process, are highly transparent because of their amorphous structure. Due to the very low refractive index (~ 1.38) of PPFC over a wide wavelength range, these thin films decrease the average reflectance by 2.22% and increase the average transmittance in the visible light region by 1.40%. As a result, the AR films increase the PCE of F-PSCs from 18.6% to 20.4%. The thin films have a self-cleaning effect due to their hydrophobic surface, excellent mechanical flexibility (bending radius: 4 mm), and high chemical stability. Accordingly, the thin films improve the long-term stability of F-PSCs in humid environments. Finally, these AR PPFC thin films can be manufactured by a roll-to-roll process, making them suitable for future use in highly efficient F-PSCs.