How Low Can You Go? Defect Quantification at the 10¹⁵ cm^–3 Level in Mixed-Cation Perovskites Using Differential Pulse Voltammetry

Reactive defects in hybrid organic–inorganic metal halide perovskites that limit material functionality and durability, factors which ultimately dictate (opto)electronic device performance, are difficult to probe. Herein, we expand an electrochemical methodology for near-valence defect quantification, using a solid-state electrolyte “top contact,” to increase energy resolution and sensitivity via a differential pulse protocol. A new low level of detection of ca. 2 × 1015 cm–3 is reported for reactive defects in a triple-cation system. We confirmed that these defects are associated with mobile iodide ions in grain boundaries and at interfaces by using iodide and bromide spiked electrolytes. The detection limit for this electrochemical method is estimated to be ca. 1014 cm–3, well below that of many electrical or spectroscopic approaches. We predict this methodology lends itself to operando defect characterization during and after processing, at scale, of extremely low defect density perovskites and related optoelectronic platforms, ultimately providing an in-line approach to real-time performance and stability optimization.