We report on solid-state mesoscopic heterojunction solar cells employing nanoparticles (NPs) of methyl ammonium lead iodide (CH₃NH₃)PbI₃ as light harvesters. The perovskite NPs were produced by reaction of methylammonium iodide with PbI₂ and deposited onto a submicron-thick mesoscopic TiO₂ 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/cm², 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 (CH₃NH₃)PbI₃ NPs into the spiro-MeOTAD followed by electron transfer to the mesoscopic TiO₂ film. The use of a solid hole conductor dramatically improved the device stability compared to (CH₃NH₃)PbI₃ -sensitized liquid junction cells.

Highly efficient quantum-dot-sensitized solar cell is fabricated using ca. 2–3 nm sized perovskite (CH₃NH₃)PbI₃ nanocrystal. Spin-coating of the equimolar mixture of CH₃NH₃I and PbI₂ in γ-butyrolactone solution (perovskite precursor solution) leads to (CH₃NH₃)PbI₃ quantum dots (QDs) on nanocrystalline TiO₂ surface. By electrochemical junction with iodide/iodine based redox electrolyte, perovskite QD-sensitized 3.6 μm-thick TiO₂ film shows maximum external quantum efficiency (EQE) of 78.6% at 530 nm and solar-to-electrical conversion efficiency of 6.54% at AM 1.5G 1 sun intensity (100 mW cm⁻²), which is by far the highest efficiency among the reported inorganic quantum dot sensitizers.

Improving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis.