Photovoltaic Performance, Optical Current Loss Simulation, and Conductive Atomic Force Microscopy Analysis of Organic Solar Cells Based on PM6:Y7

In this work, an investigation of the photovoltaic (PV) performance of organic solar cells (OSCs) based on PM6:Y7, in combination with a conductive atomic force microscopy (c-AFM) study, is presented. OSCs were fabricated and tested under regular atmospheric conditions, employing the conventional structure glass/ITO/PEDOT:PSS/PM6:Y7/PFN/Field’s metal (FM) where FM, a eutectic alloy of Bi, In, and Sn, served as an alternative top electrode, deposited easily via drop casting at 95 °C, eliminating the requirement of a high-vacuum chamber. An optimum active film thickness of 72 nm is identified for the PV devices, reaching a power conversion efficiency (PCE) of 11.44 ± 0.22% (best PCE = 11.76%). Further, optical constants (n and k) were determined for PEDOT:PSS, PM6:Y7, and PFN films via modeling of transmittance data; these parameters were used to simulate the external quantum efficiency response, which provided the optical performance-limiting factors across all cell layers and interfaces within the OSC. Likewise, topography measurements showed that the 72 nm-thick PM6:Y7 film exhibited a relatively low roughness of 1.7 nm, obtained without the use of postprocessing methods. The c-AFM quantitative analysis was carried out on the active film with and without the electron transport interfacial layer (PFN) of the cell structure, which confirmed that the addition of PFN on top of PM6:Y7 enhanced conductive pathways with high current and low resistance values.