PEDOT:PSS on flexible black silicon for a hybrid solar cell on textured polyimide substrate

This work investigates properties of PEDOT:PSS on flexible black silicon (bSi) for a hybrid solar cell on textured polyimide (PI) substrate. The flexible bSi is formed by thinning down crystalline silicon (cSi) wafers to 65 μm thickness, followed by fabrication of bSi nanowires (NWs) on the wafer surface using one-step metal-catalyzed electroless etching (MCEE) technique. The resulting bSi NWs exhibit an average diameter of around 90-100 nm and length of 900 nm. Then, PEDOT:PSS with a thickness of 150 nm is coated on the flexible cSi and bSi NWs. For texturing of PI, copper-seeding technique is used. The planar and textured PI substrates are then attached to the back of the flexible cSi and bSi. The PEDOT:PSS/flexible bSi on PI substrate shows lower broadband reflection when compared to PEDOT:PSS/flexible cSi. This is due to the presence of bSi NWs on wafer surface which leads to refractive index grading effect. The PEDOT:PSS/flexible bSi solar cell on the textured PI substrate demonstrates conversion efficiency of 2.58%. This is contributed by the increased short-circuit current density (J_sc) in the device (when compared to the device on planar PI), owing to the enhanced light absorption above wavelength of 800 nm.