Al₂O₃‐Atomic Layer Deposited Films on CH₃NH₃PbI₃: Intrinsic Defects and Passivation Mechanisms

Abstract

The initial interaction of atomic layer deposited films of Al2O3 at room temperature on CH3NH3PbI3 (MAPI) films is studied. Synchrotron radiation–based photoelectron spectroscopy is applied to analyze the initial changes in the Al‐derived features by comparing samples with different Al2O3 film thicknesses. It is found that polarons and excitons, both intrinsic defects of Al2O3, play a key role in the interface formation. The polaronic states uptake a charge from the MAPI substrate. This charge is transferred to and stabilized in the excitonic state of Al2O3 which is assigned to predominately tetrahedral coordinated Al sites. This charge transfer is initiated by vacancies present in the MAPI substrate and stabilizes a covalent bonding at the Al2O3–MAPI interface but also causes a roughening of the interface which may lead to the formation of grain boundaries. On top of the rough interface, 2D Al2O3 clusters with an increasing number of octahedrally coordinated Al—O bonds grow, and with increasing Al2O3 coverage, they introduce self‐healing of the structural defects.

The chemistry and energetics of the interface between metal halide perovskite and atomic layer deposited metal oxides

“…27 A similar behavior was reported by Yu et al 29 Synchrotron XPS analysis was employed by Kot et al, 30 which indicated that the interaction of ALD precursors occurs only at the surface of the CH 3 NH 3 PbI 3 and FA 0.85 MA 0.15 Pb(Br 0.15 I 0.85 ) 3 perovskite (where FA corresponds to the formamidinium cation) during the growth of Al 2 O 3 at room temperature. 23,24 In parallel, they showed that there is covalent bonding at the CH 3 NH 3 PbI 3 /Al 2 O 3 interface. At the same time, they identified a charge balance between the polaronic and excitonic states in CH 3 NH 3 PbI 3 and Al 2 O 3 .…”

“…So far, Al 2 O 3 is considered the only successful case of direct ALD processing on the perovskite absorber. 12,[23][24][25] A recent work from our group using infrared (IR) and x-ray photoelectron spectroscopy (XPS) analysis revealed that the interaction between H 2 O (used as coreactant) and CH 3 NH 3 PbI 3−x Cl x was negligible under the conditions adopted in the ALD recipe. 26 On the contrary, exposure to trimethylaluminum (TMA, used as metal precursor) was found to degrade the perovskite surface, leading to the effusion of methylammonium (MA) cations.…”

“…At the same time, they identified a charge balance between the polaronic and excitonic states in CH 3 NH 3 PbI 3 and Al 2 O 3 . 23 In the case of ETLs, the chemistry of the metalorganic precursor plays a critical role. 5,8,10 For ZnO, the diethyl-Zn (DEZ) precursor strongly reacted with the organic component of the hybrid perovskite leading to its complete decomposition.…”

Top‐Down Approach to Study Chemical and Electronic Properties of Perovskite Solar Cells: Sputtered Depth Profiling Versus Tapered Cross‐Sectional Photoelectron Spectroscopies

“…[ 2 ] The electronic and chemical properties of the film in the bulk and at interfaces in the PSCs are often studied directly using various microscopic and spectroscopic methods. [ 5,6 ] In particular, time of flight secondary ion mass spectroscopy (ToF‐SIMS), transmission electron microscopy (TEM) [ 7–10 ] and field emission secondary electron microscopy (FESEM) [ 11 ] are used. The distribution of organic and inorganic cations has been determined over the whole thickness of the mixed cation‐based PSCs using ToF‐SIMS.…”

ITO/SnO2 Interface Defect Passivation via Atomic Layer Deposited Al2O3 for High‐Efficiency Perovskite Solar Cells

“…[15] Moreover, Schmeißer and co-workers found that polarons and excitons, both intrinsic defects of Al 2 O 3 , easily bond to the perovskite crystalline surface by the covalent and ionic bond, of which the interaction between Al 2 O 3 and perovskite is of benefit for electron extraction. [28,29] Yang and co-workers used the thin Al 2 O 3 film to encapsulate PSCs to efficiently enhance the long-term stability for 2100 h under 80% relative humidity and at 30 C. [30] Apart from the ETL/perovskite and perovskite/HTL interfaces, the ITO/ETL interface also shows a remarkable impact on the electron extraction efficiency of conventional PSCs. The surface defects and micropores at the interface would retard the charge extraction, consequently increasing nonradiative recombination and enlarging the hysteresis phenomenon.…”