A simple approach for improving the photovoltaic efficiency of organic solar cells through polymer modification via anion exchange as the interlayer

A simple anion exchange was used to synthesize polyelectrolytes based on naphthalene diimide (NDI), which were then applied as a cathode interlayer in organic solar cells (OSCs). These polyelectrolytes can be dissolved in alcohols and produce a beneficial interface dipole due to the ionic functionality in the side chain. The PCE of the OSC utilizing PFN-NDI-OH as the cathode interlayer showed an enhancement compared to the pristine ZnObased device, increasing from 8.79 % to 8.91 %. This improvement can be attributed to the polar nature of PFN-NDI-OH, which facilitates a strong adhesion between the inorganic metal oxide and the organic active layer. The device with PFN-NDI-OTs exhibited an enhanced PCE of up to 9.41 % due to the size of the counteranion was found to be related to the PCE, as converting the hydroxide to a tosylate anion increased the PCE, with the larger size of the tosylate anion playing a role in enhancing the Jsc. These results indicate that these polyelectrolytes are a promising candidate for use as a cathode interlayer in OSCs, with the additional advantage of being able to improve interfacial properties through a simple anion exchange process without time-consuming purification steps.