Designs of Flexible Transparent Electrodes with Antireflection Coatings for High Performance Flexible Perovskite Solar Cells

Flexible perovskite solar cells (F-PSCs) are of great interest because of their flexibility, light weight, portability, and compatibility with various form factors including curved surface, and low fabrication cost. Despite of enormous potential in applications, 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. In this regard, we propose a newly developed plasma-polymerized-fluorocarbon (PPFC) thin film as an antireflection (AR) coating material for enhancing the efficiency of F-PSCs. The PPFC is a thin film with an amorphous structure produced by sputtering a composite target made by mixing PTFE and carbon nanotubes. The PPFC thin films have excellent AR effect due to low refractive index (~1.38), good adhesion to the substrate, uniformity of nanometer-level thickness and water repellency. When PPFC AR coating are deposited on the flexible polyethylene terephthalate (PET) substrates, the average difference in the transmittance of PPFC/PET increases by 3.23%, and the average difference in reflection decreases by 3.23%. After coating the PET/ITO with 100 nm PPFC film, the average difference in the reflectance decreases by 2.22%, and the average difference in transmittance increases by 1.40% in the visible region, resulting in maximum light transmittance due to the AR effect. The PPFC thin film is employed to improve the efficiency of F-PSCs, thereby increasing light absorption in the perovskite layer, and finally enhances the photocurrent in the F-PSCs. The enhanced photocurrent in the F-PSCs with the PPFC thin film is also verified by measuring the external quantum efficiency (EQE) spectra of F-PSCs without and with the PPFC thin film. All the F-PSCs with the PPFC thin film shows increased EQE in the entire visible range. The optimized F-PSCs with the 100 nm PPFC thin film greatly improves the PCE of F-PSCs from 18.6% to 20.4%. In addition, PPFC thin film have a hydrophobic surface and very flexible, its properties is enhanced the device stability against under harsh environmental conditions. These PPFC thin films are expected to be useful not only for F-PSCs but also for flexible electronic devices in general, considering their excellent broadband light enhancement properties, self-cleaning surface, environmental stability and flexibility.