Passivation Properties and Formation Mechanism of Amorphous Halide Perovskite Thin Films

Abstract

Lead halide perovskites are among the most exciting classes of optoelectronic materials due to their unique ability to form high‐quality crystals with tunable bandgaps in the visible and near‐infrared using simple solution precipitation reactions. This facile crystallization is driven by their ionic nature; just as with other salts, it is challenging to form amorphous halide perovskites, particularly in thin‐film form where they can most easily be studied. Here, rapid desolvation promoted by the addition of acetate precursors is shown as a general method for making amorphous lead halide perovskite films with a wide variety of compositions, including those using common organic cations (methylammonium and formamidinium) and anions (bromide and iodide). By controlling the amount of acetate, it is possible to tune from fully crystalline to fully amorphous films, with an interesting intermediate state consisting of crystalline islands embedded in an amorphous matrix. The amorphous lead halide perovskite has a large and tunable optical bandgap. It improves the photoluminescence quantum yield and lifetime of incorporated crystalline perovskite, opening up the intriguing possibility of using amorphous perovskite as a passivating contact, as is currently done in record efficiency silicon solar cells.

Disentangling X‐Ray and Sunlight Irradiation Effects Under a Controllable Atmosphere in Metal Halide Perovskites

“…The explanation could be a self‐doping process by the amorphous perovskite combined with air passivation. [ 40 ] We associated the diffraction peak intensity decrease to an amorphization process, but a definitive proof would be observing the amorphous phase itself, which our X‐ray diffraction data cannot reach. Concerning the sample 40:38, the fact that no shift in the XEOL emission band has been observed, even though a new bromine‐rich phase showed up, must be related to the band‐edges of the new phase, whose lattice parameter is shorter and bandgap larger, falling into the valence and conduction bands of the pristine phase.…”

Sequential vacuum-evaporated perovskite solar cells with more than 24% efficiency

“…No obvious signal was observed at 0.1° (fig. S6), indicating the absence of a crystalline phase at the top surface of the film before annealing, and we inferred it to be the formation of an amorphous phase by the excessive FAI on top ( 29 ). For the incident angle of 2°, several different diffraction signals appeared.…”

Structure and electronic properties of amorphous strontium titanate

“…Understanding how the local structure and morphology of perovskite materials change upon amorphization is key to establishing the structure-property relationships in the disordered materials and may open up new research avenues and opportunities [12,[21][22][23][24]. For amorphous STO, the coordination of Ti remains under debate: while it is typically argued in literature that the good properties of a-STO are due to the TiO 6 (octahedral) coordination being maintained in the disordered phase, two experimental studies that employed extended x-ray absorption fine structure (EXAFS) measurements infer contradictory results with octahedral [17] and tetrahedral [20] Ti coordination.…”