Oxygen Degradation in Mesoporous Al₂O₃/CH₃NH₃PbI_3‐xCl_x Perovskite Solar Cells: Kinetics and Mechanisms

Abstract

unexpectedly clean electronic properties of these semiconductors have led to the demonstration of proof-of-concept PV devices with an initial effi ciency that outperforms competing 'next-generation' technologies such as dye-sensitized, organic, and quantum dot solar cells, and even matches that of commercially deployed PV. [ 6 ] Other attractive characteristics of hybrid perovskites include the low embedded costs of materials processing and the ability to tune the properties of the semiconductor through changes in chemical composition. [ 1,[7][8][9][10] All of these factors have led to hybrid perovskites being considered as disruptive materials in a wide range of technology applications; [11][12][13][14][15][16] interest from the materials science research community is both substantial and rapidly maturing. Realizing the technology potential of hybrid perovskites necessitates a thorough understanding of the degradation mechanisms that limit the lifetime of devices, and identifying solutions to mitigate these. This exercise is nontrivial because of the various factors that can affect device performance: light, heat, moisture, oxygen, mechanical and electrical stresses, and combinations thereof. [ 17,18 ] Currently, perovskite solar cells (PSCs) based on the "triple layer" architecture with a thick carbon back electrode have demonstrated perhaps the most stable performance characteristics of all PSCs. [ 19 ] These devices, based on the mixed cation perovskite (5-AVA) X (MA) 1− X PbI 3 (where 5-AVA corresponds to 5-ammoniumvaleric acid), have been shown to maintain their initial power conversion effi ciency (PCE) of approximately 10% over 1000 h continuous simulated solar illumination, [ 20 ] dark storage for three months at elevated temperatures and humidity (85 °C/85%) and a minimum of 7 d operation in real-world conditions (Jeddah, Saudi Arabia). [ 21 ] Although clearly commendable, it is apparent that signifi cant work is required to realize PSCs with high stability and high performance, where promising stability metrics are combined with the certifi ed PCE values for champion devices. [ 22 ] To elucidate the underlying mechanisms for degradation in hybrid perovskites and guide the development of intrinsically stable devices, considerable work has been undertaken on the archetypal semiconductor of the research fi eld: CH 3 NH 3 PbI 3 . It is known that this material (and other single or mixed-halide derivatives) are particularly sensitive to moisture, [ 1,7,17,[23][24][25][26] where the proposed chemical reactions involving water result in decomposition of the perovskite into its precursor components via The rapid pace of development for hybrid perovskite photovoltaics has recently resulted in promising fi gures of merit being obtained with regard to device stability. Rather than relying upon expensive barrier materials, realizing market-competitive lifetimes is likely to require the development of intrinsically stable devices, and to this end accelerated aging tests can help identify degradation mechanisms tha...

Achieving Long‐Term Operational Stability of Perovskite Solar Cells with a Stabilized Efficiency Exceeding 20% after 1000 h

“…Photocatalytic chemical reaction with absorption of ultraviolet (UV) light by TiO 2 is considered to induce achieved. [16,17] Haque and co-workers claimed that the degradation stems from the formation of reactive superoxide species in mediating halide vacancies in the perovskite materials. Even small amounts of oxygen can affect performances of PSCs since oxygen can easily react with halides.…”

Efficient and Air‐Stable Mixed‐Cation Lead Mixed‐Halide Perovskite Solar Cells with n‐Doped Organic Electron Extraction Layers

“…[5,[51][52][53] In addition, the MAPbI 3 has also been shown to degrade more rapidly when exposed to light in an atmosphere containing oxygen, due to a chemical reaction between oxygen and MA + in the presence of electronic charge in the perovskite. [54] We have previously shown that formamidinium (FA)-based perovskites are much more thermally stable than methylammonium (MA)-based perovskite. [48,55] One problem with FAPbI 3 however is that it is not structurally stable in the black perovskite phase and undergoes a phase transition to a yellow phase at room temperature.…”

“…Our perovskite cells composed of p and n-doped organic charge extraction layers are reasonably stable in air (which includes oxygen and moisture) and full spectrum sun light that includes the UV component, which indicates that the perovskite solar cells (this perovskite in this architecture) are not as sensitive to these environmental stressing components as previously thought. [18][19][20][21]49,54,64,65] 2. The n-doping of the C 60 appears to have a persistent beneficial effect over prolonged operation in air, indicating that the N-DPBI retains its doping function throughout the ageing test.…”

Research Update: Strategies for improving the stability of perovskite solar cells

“…6,[67][68][69][70][71] Ambient oxygen in combination with light can lead to direct photo-oxidation of the MAPbI 3 perovskite. 68,69 Those studies suggest that the accumulation of photogenerated electrons accelerates the oxygen-induced degradation of the perovskite absorber. Possible strategies for mitigating the oxygen assault on devices could therefore include effective barrier layers and oxygenimpermeable encapsulants, as well as efficient electron extraction layers.…”