Film-forming polymer nanoparticle strategy for improving the passivation and stability of perovskite solar cells

Abstract

Perovskite solar cells (PSCs) provide excellent potential for large-scale solar energy harvesting because of their high power conversion efficiency (PCE) and facile preparation. However, long-term stability remains the Achilles heel for PSCs and new methods for improving stability are urgently needed. Film-forming polymer nanoparticles are widely used in the surface coatings industry to provide scalable, low-cost protection to surfaces. Inspired by this, here we add three soft, film-forming crosslinked polymer nanoparticle systems (nanogels) with different diameters (60, 100 and 200 nm) to the perovskite (FA_0.75MA_0.25PbI₃) precursor solution and study their effects on PSC performance. The nanogels contain hydrophilic ethylene oxide repeat units and form films when their diameter is less than or equal to 100 nm. Device stability was assessed using shelf-life and light-soaking measurements; in addition, films were subjected to moisture challenge tests. We show that nanogel coverage increases the PCE and stability. Ab initio simulations indicate strong binding of the molecules that comprise the nanogels on the perovskite surface through Pb–O bonds, thereby promoting enhanced surface stability in agreement with the XPS and FTIR signals associated with the binding of the CO and C–O groups to Pb. Shelf-life stability measurements showed that nanogels with a diameter of 100 nm gave devices that retained >80% of their initial PCE after more than six months compared to 25% for the control. In contrast, the 200 nm nanogels did not form films or increase the PCE or shelf-life stability. The 100 nm nanogels also gave the best stability to light soaking. Our results show that highly deformable hydrophilic film-forming nanogel particles with a size of ∼100 nm provide a scalable alternative approach for improving passivation and stability of PSCs.