The First Solid-State Halide Perovskite Solar Cell

RecommendationsH alide perovskites can function as solution-processable, direct-gap semiconductor absorbers in fully solid-state photovoltaic devices.We established this by demonstrating, in early 2012, an all-solid-state, Graetzel-type mesoscopic device in which CsSnI 3 functioned as a p-type semiconductor replacing the liquid electrolyte and, because of its strong visible to near-infrared absorption, contributed substantially to light harvesting and photocurrent generation.This operating principle differs fundamentally from dye-sensitized solar cells, where absorption is molecular and charge transport relies on a liquid electrolyte.The device concept was enabled by establishing that tin halide perovskites are direct-band gap semiconductors, whose apparent metallic transport arises from defect-controlled self-doping rather than intrinsic metallicity, and that they can be processed from solution into continuous thin films.By establishing the perovskite as an active semiconductor layer rather than a sensitizer, this work defined a new photovoltaic platform that underpins subsequent advances in thin-film solid-state perovskite solar cells.The emergence of halide perovskites as photovoltaic materials is one of the most rapid transitions in contemporary materials science.In a short time window, a class of compounds that had been studied mainly as optoelectronic curiosities became a central platform for solar energy research.When such transitions happen quickly, the early years often get compressed into a simplified sequence, which can blur the scientific steps that made later advances possible.The purpose of this article is not to provide a comprehensive review.Rather, it is to describe, with specific experimental signposts, how our work progressed from early tin halide perovskite studies to a solid-state perovskite solar cell demonstration in 2012, 1 and how that demonstration fits within the broader landscape of parallel efforts. 2,3I also want the central message to be easy for the reader to follow in terms of chronology, scientific rationale, and mechanism: our 2012 demonstration established that a compact perovskite film can act as the dominant absorber and a functional semiconducting layer in an all-solid solar cell stack.It is equally important to frame this in a way that gives fair credit to the field's intellectual roots.The mesoscopic dyesensitized solar cell architecture, pioneered and advanced by Michael Graetzel and colleagues three decades earlier, 4 motivated the early community and provided a device language that many groups used as they searched for new absorber concepts.In that sense, Graetzel's work motivated the trajectory that made perovskite photovoltaics possible.The distinct contribution described here is that the absorber can be a halide perovskite semiconductor layer that enables fully solidstate operation and supports efficient charge extraction without a liquid redox electrolyte.