Spin and doctor-blade coated PEDOT:PSS back electrodes in inverted organic solar cells

Abstract

Spin and doctor-blade coated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) back electrodes are evaluated in inverted organic solar cells (OSCs) geometry. The doctor-blade coating which has the potential to be used in roll-to-roll processing, is demonstrated by coating PEDOT:PSS manually over the active layer and hence, this sets-up an effort for the concept of much easier fabrication options for large-scale manufacturing like hand-painting, sketching etc. The spin and doctor-blade coated PEDOT:PSS films showed comparable sheet resistance values of 39.7 ± 2.3 and 40.2 ± 5.5 Ω/□ respectively for a thickness of ≈400 nm. The absorbance in the active layer (≈0.7 at 500 nm) had negligible effect due to these coating styles of PEDOT:PSS layer as well as its thickness. The OSC devices that have PEDOT:PSS electrodes formed by the two coating methods were fabricated, characterized, and comparatively evaluated. The results demonstrated an on-par performance for films as well as devices with a manually doctor-blade coated PEDOT:PSS layer when compared to devices that have a spin-coated PEDOT:PSS layer. The atomic force microscopy probe reveals similar surface morphological behaviour for two coating styles with surface roughness values of 16.5 ± 4.1 nm and 17.4 ± 4.9 nm for spin and manual-doctor-blade coating methods, respectively. From spectral response measurement, the evaluated variation in the charge collection efficiency, ηcc at the interface between active layer and PEDOT:PSS interface was within 6% of error for both kind of devices. It indicates similar interface behaviour for both coating styles of PEDOT:PSS, reinforcing the similar performance of manually-doctor-blade coated PEDOT:PSS electrode to that of spin coated one.