Mechanisms for light induced degradation in MAPbI3 perovskite thin films and solar cells

Abstract

Organometal halide perovskites are highly promising materials for photovoltaic applications, yet their rapid degradation remains a significant challenge. Here, the light-induced structural degradation mechanism of methylammonium lead iodide (MAPbI3) perovskite films and devices is studied in low humidity environment using X-Ray Diffraction, Ultraviolet-Visible (UV-Vis) absorption spectroscopy, Extended X-ray Absorption Fine Structure spectroscopy, Fourier Transform Infrared spectroscopy, and device measurements. Under dry conditions, the perovskite film degrades only in the presence of both light and oxygen, which together induce the formation of halide anions through donation of electrons to the surrounding oxygen. The halide anions generate free radicals that deprotonate the methylammonium cation and form the highly volatile CH3NH2 molecules that escape and leave pure PbI2 behind. The device findings show that changes in the local structure at the TiO2 mesoporous layer occur with light, even in the absence of oxygen, and yet such changes can be prevented by the application of UV blocking layer on the cells. Our results indicate that the stability of mp-TiO2-MAPbI3 photovoltaics can be dramatically improved with effective encapsulation that protects the device from UV light, oxygen, and moisture.

Role of Microstructure in Oxygen Induced Photodegradation of Methylammonium Lead Triiodide Perovskite Films

“…The combination of reduced grain size throughout the film and a higher defect density serve as the cause for a lower fill factor (FF) and short-circuit current density (J SC ) in sol-eng devices, resulting in a lower overall efficiency. [18,20,48] This observation and our measurements of the local temperature demonstrate that light induced heating effects alone do not result in a degradation of the perovskite film on this timescale and the observed degradation is a consequence of exposure to light and oxygen. [42,45,46] For the PbAc 2 recipe, the inherent water in the precursor solution as well as the addition of hypophosphorous acid results in an enlargement of the grain size and improved film morphology resulting in perovskite films with high electronic quality and low defect density.…”

“…[2] Although the issue of device stability has attracted increased attention of the photovoltaic research community in the last two years, reports that systematically study the fundamental causes (e.g., heat, electrical stress, humidity, oxygen, (UV) light, chemical precursors, processing conditions, influence of film quality and morphology) and mechanisms limiting the material and device stability remain scarce. [16][17][18][19][20] It has been shown that photoexcited electrons in the perovskite layer can form superoxide (O 2 − ) via electron transfer to molecular oxygen, which through deprotonation of the methylammonium cation in turn results in irreversible material degradation. [16][17][18][19][20] It has been shown that photoexcited electrons in the perovskite layer can form superoxide (O 2 − ) via electron transfer to molecular oxygen, which through deprotonation of the methylammonium cation in turn results in irreversible material degradation.…”

Understanding Hydrogen Bonding Interactions in Crosslinked Methylammonium Lead Iodide Crystals: Towards Reducing Moisture and Light Degradation Pathways

“…In am oisture-free environment, the combination of O 2 and light may also lead to the degradation of CH 3 NH 3 PbI 3 .As per Reactions (8) and (9), CH 3 NH 3 PbI 3 reacts with O 2 to form an O 2 À radical which then reacts with the CH 3 NH 3 + cation to yield CH 3 NH 2 ,P bI 2 ,I 2 ,and H 2 O. [44] CH 3 NH 3 PbI 3 ðsÞþO 2 $ hn CH 3 NH 3 PbI 3 * ðsÞþO 2 * À ð8Þ…”

“…[4][5][6][7][8] These approaches include modification of the perovskite structure via halide engineering, [9][10][11][12] cation substitution and the addition of dopants, [13][14][15][16][17] interface engineering, [18][19][20][21][22] and surface passivation [23] or encapsulation via small molecules or waterproof layers. [4][5][6][7][8] These approaches include modification of the perovskite structure via halide engineering, [9][10][11][12] cation substitution and the addition of dopants, [13][14][15][16][17] interface engineering, [18][19][20][21][22] and surface passivation [23] or encapsulation via small molecules or waterproof layers.…”

Perovskite Quantum Dots and Their Application in Light‐Emitting Diodes

“…Studies focused on colloidal PQDs because of their good optoelectronic properties and high PLQY in nonpolar solvents. Stability of PQDs poses a major problem for practical applications in LEDs.…”