Graphitic Carbon Nitride Nanosheets: Dual Functional Charge Selective Cathode/Anode Interface Layer for Polymer Solar Cells

Here, we report a systematic study proposing the utilization of graphitic carbon nitride nanosheets (g-C3N4 NS) thin film as a charge-selective cathode/anode interface layer for inverted as well as conventional polymer solar cells. The pristine ITO/g-C3N4 NS thin film-based electrodes were found to have a work function value of approximately 4.43 eV making them a potential candidate as a cathode interface layer for inverted devices. The work function value increased to similar to 5.25 eV after UV-ozone treatment, befitting as an anode interface layer for conventional PSCs. The device with g-C3N4 NS as the interface layer exhibited similar short circuit current density for both inverted and conventional device architecture. This confirms the dual functionality of the g-C3N4 NS thin film in terms of charge-selectivity for efficient carrier collection. The overall power conversion efficiency for the two devices was approximately 5.60% and 6.05%, respectively. The UV-ozone treatment seems to alter the work function of g-C3N4 NS thin film by inducing surface dipoles due to the incorporation of oxygen atoms. This results in switching from electron-extracting behavior to hole extraction. Our results demonstrate the dual functional nature of g-C3N4 NS as an interface layer (CIL/AIL) for solution-processable polymer solar cells.