Simple route to interconnected, hierarchically structured, porous Zn₂SnO₄ nanospheres as electron transport layer for efficient perovskite solar cells

Constructing electron transport layer (ETL) with higher carrier mobility and suitable bandgap is of key importance as it greatly influences the photovoltaic performance of perovskite solar cells (PSCs). Zn₂SnO₄ (ZTO) carries a high electron mobility of 10–30 cm² V⁻¹ s⁻¹, an order of magnitude over the widely used TiO₂ ETL in PSCs, rendering it an excellent alternative to TiO₂ ETL. Herein, we report a simple yet robust polymer-templating route to interconnected, hierarchically structured, porous ZTO nanospheres as an efficient ETL for high-performance organolead halide PSCs. The porous ZTO nanospheres ETL, composed of an assembly of 4.5-nm ZTO nanoparticles on the surface of porous nanosphere possessing 80–100 nm cavity, renders markedly improved light absorption, enhanced electron extraction, facilitated charger transportation, and suppressed carrier recombination in the resulting PSCs, which exhibit a power conversion efficiency (PCE) of 17.14%, greatly outperforming the device based on the ZTO nanoparticles (14.02%; i.e., without porosity). As such, the strategy for crafting porous yet hierarchically structured semiconductors with high carrier mobility may open up an avenue to create robust ETL, and by extension, hole transport layer (HTL) for high-performance optoelectronics.