Effect of the Side Chain Functionality of the Conjugated Polyelectrolytes as a Cathode Interlayer Material on the Photovoltaic Performances

Novel Polyelectrolytes Based on Naphthalene Diimide with Different Counteranions for Cathode Interlayers in Polymer Solar Cells

We synthesized novel polyelectrolytes based on naphthalene diimide with quaternary amine featuring hydroxyl groups at the side chain, along with different counteranions (PF-NDIN-Br-OH and PF-NDIN-I-OH) for polymer solar cell (PSC) application as the interlayer. The polyelectrolytes establish a beneficial interface dipole through the ionic moieties and synergistic effects arising from the hydroxyl groups located at the side chain. Incorporating polyelectrolytes as the cathode interlayer resulted in an enhancement of the power conversion efficiency (PCE). The PCE of the device with PF-NDIN-Br-OH increased from 8.96% to 9.51% compared to the ZnO-only device. The best PCE was obtained with the device based on PF-NDIN-I-OH, up to 9.59% resulting from the Jsc enhancement. This outcome implies a correlation between the performance of the device and the synergistic effects observed in polyelectrolytes containing hydroxyl groups in the side chain, along with larger anions when employed in PSCs.

Anionic Conjugated Polyelectrolyte as a Semiconducting Additive for Efficient and Stable Perovskite Solar Cells

Perovskite defects are a major hurdle in the efficiency and stability of perovskite solar cells (PSCs). While various defect passivation materials have been explored, most are insulators that hinder charge transport. This study investigates the potential of two different π-conjugated polyelectrolytes (CPEs), MPS2-TEA and PCPDTBT2-TMA, as semiconducting additives in PSCs. The CPEs differ in electrical conductivity, offering a unique approach to bridge defect mitigation and charge carrier transport. Unlike previous uses of CPEs mainly as interlayers or charge transport layers, we explore their direct effect on defect passivation within a perovskite layer. Secondary ion microscopy reveals the even distribution of CPEs within the perovskite layer and their efficient defect passivation potential is studied through various spectroscopic analyses. Comparing MPS2-TEA and PCPDTBT2-TMA, we find MPS2-TEA to be superior in defect passivation. The highly conductive nature of PCPDTBT2-TMA due to self-doping diminishes its defect passivation ability. The negative sulfonate groups in the side chains of PCPDTBT2-TMA stabilize polarons, reducing defect passivation capability. Finally, the PSCs with MPS2-TEA achieve remarkable power conversion efficiencies (PCEs) of 22.7% for 0.135 cm2 and 20.0% for large-area (1 cm2) cells. Furthermore, the device with MPS2-TEA maintained over 87.3% of initial PCE after 960 h at continuous 1-sun illumination and 89% of PCE after 850 h at 85 °C in a nitrogen glovebox without encapsulation. This highlights CPEs as promising defect passivation additives, unlocking potential for improved efficiency and stability not only in PSCs but also in wider applications.