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Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%

Why this mattered

This paper mattered because it helped turn halide perovskites from an unstable curiosity in dye-sensitized, liquid-electrolyte cells into a credible solid-state photovoltaic absorber. Earlier methylammonium lead halide cells had shown strong light harvesting but were limited by dissolution and rapid degradation in liquid electrolytes. By replacing the liquid junction with the solid hole conductor spiro-MeOTAD and using mesoporous TiO₂ as the electron-collecting scaffold, Kim and colleagues demonstrated that perovskite sensitizers could deliver both high photocurrent and substantially improved operational stability. The reported 9.7% efficiency was not merely an incremental record; it showed that a solution-processable, submicron absorber could compete with far more established thin-film concepts.

The deeper shift was conceptual. The device was still framed as a “sensitized” mesoscopic solar cell, but the measured performance and ultrafast spectroscopy pointed toward a material that was doing more than behaving like a conventional dye. Methylammonium lead iodide absorbed strongly, generated charge efficiently, and supported charge separation through both hole injection into spiro-MeOTAD and electron transfer to TiO₂. This made it plausible that organometal halide perovskites could function as the central photovoltaic semiconductor, not just as a molecular light harvester attached to an oxide surface.

That realization opened the path to the rapid perovskite solar-cell surge that followed: higher-efficiency solid-state mesoscopic devices, planar thin-film architectures, mixed-halide and mixed-cation compositions, improved transport layers, and eventually tandem cells with silicon. Later work would move beyond the exact architecture used here and address major weaknesses such as hysteresis, moisture sensitivity, ion migration, and lead toxicity. But this 2012 result supplied one of the decisive proofs that perovskite photovoltaics could be efficient, solid-state, and manufacturable by low-temperature solution methods, making the field newly worth a global research race.

Abstract

We report on solid-state mesoscopic heterojunction solar cells employing nanoparticles (NPs) of methyl ammonium lead iodide (CH(3)NH(3))PbI(3) as light harvesters. The perovskite NPs were produced by reaction of methylammonium iodide with PbI(2) and deposited onto a submicron-thick mesoscopic TiO(2) film, whose pores were infiltrated with the hole-conductor spiro-MeOTAD. Illumination with standard AM-1.5 sunlight generated large photocurrents (J(SC)) exceeding 17 mA/cm(2), an open circuit photovoltage (V(OC)) of 0.888 V and a fill factor (FF) of 0.62 yielding a power conversion efficiency (PCE) of 9.7%, the highest reported to date for such cells. Femto second laser studies combined with photo-induced absorption measurements showed charge separation to proceed via hole injection from the excited (CH(3)NH(3))PbI(3) NPs into the spiro-MeOTAD followed by electron transfer to the mesoscopic TiO(2) film. The use of a solid hole conductor dramatically improved the device stability compared to (CH(3)NH(3))PbI(3) -sensitized liquid junction cells.

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