Perovskite films passivated by poly[(R)-3-hydroxybutyric acid] for improved photovoltaic performance

Polymer is one of the most effective passivation additives in perovskite solar cells (PSCs). Herein, we apply a polymer Poly[(R)-3-hydroxybutyric acid]) (PHB) to passivate the defects and traps in the perovskite films due to the presences of C=O functional group in the structure of PHB. The FTIR result demonstrates the PHB has chemical interaction with perovskite films, which can decrease the Pb trap density on the surface of films. As a result, the PCE of PSCs increases from 18.92% to 20.20%, and the average Voc increases from 1.07 V to 1.11 V due to PHB passivation. The hydrophobic properties of the alkyl chains on the polymer enhance the stability of the devices. The device without PHB passivation degrades to ∼72% of the initial PCE, whereas the PCE of the device with PHB still exhibit 98% of its initial PCE as the devices are kept under 25 ± 5% RH and 30 ± 5 °C condition for 14 days. For high humidity condition (60 ± 5% RH for 350 min), The device with PHB can keep ∼ 75% of the original PCE value, but the control device can only maintain ∼45% of the initial value. This work presents a new strategy to increase the efficiency and stability of PSCs by two function groups C=O and alkyl chains.