Polymer-complexed SnO₂ electron transport layer for high-efficiency n-i-p perovskite solar cells

An effective electron transport layer (ETL) plays a pivotal role in suppressing nonradiative recombination at the interface as well as promoting perovskite crystallization to facilitate electron extraction in perovskite solar cells (PSCs). Herein, a functional polymer, poly(amidoamine) (PM) dendrimer, is introduced to rationalize the morphology and electrical performance of SnO₂ nanocrystals to construct an SnO₂ charge transfer layer. PM offers an even SnO₂ colloidal dispersion with a particle-size distribution of ∼10 nm, which prevents the agglomeration of nanocrystals significantly. The polymer-complexed SnO₂ provides a uniform and dense ETL film without island-like agglomeration, yielding a large conductive layer superior to that of the control. Equally important, the wettability-improved SnO₂ ETL with PM modification produces a high-quality perovskite film with larger grain size, resulting in a power conversion efficiency (PCE) of the champion n-i-p PSC of up to 22.93% with negligible hysteresis. Noticeably, the device based on SnO₂-PM maintained 71% of its initial PCE (only 49% for the control device) after storing in the ambient environment for 45 days (relative humidity of 30%-80%) without packaging.