Rational design of nanogel particle composition to control halide perovskite growth, structure and increase solar cell efficiency

The purpose of this study is to apply pH-responsive nanogels, previously used for load-bearing biomaterials and colloidosomes, to the challenge of improving the properties of halide perovskite (HP) films and perovskite solar cell (PSC) power conversion efficiency (PCE). Our results show that nanogel composition is critical for their use in the HP precursor solutions and that methacrylic acid (MAA) has multiple beneficial effects. MAA groups in the nanogels catalyze HP crystallization and increase conversion of PbI 2 to HP. The nanogels are shown to be present at the top and bottom (buried) HP surfaces as well as between grains. By varying the composition of the nanogels we identify PEA-MAA-DVB (EA and DVB are ethyl acrylate and 1,4-divinylbenzene) as an optimal nanogel system in terms of PCE. The nanogels are shown to bind HP grains to each other as well as to the underlying SnO 2 transport layer. The nanogels decrease the rate of HP film degradation to moisture and increase PSC stability. They are also shown to passivate defects at the HP surface decreasing non-radiative recombination which increases the PCE to the highest value reported to date for PSCs containing nanogels. We conclude that all parts of the nanogel structure are essential for these adhesive and binding colloidal additives to improve HP properties and PSC performance. The results of this study provide a pathway to future nanogel design improvements for use in PSCs.