Effect of Electron‐Transport Material on Light‐Induced Degradation of Inverted Planar Junction Perovskite Solar Cells

Abstract

This paper presents a systematic study of the influence of electron‐transport materials on the operation stability of the inverted perovskite solar cells under both laboratory indoor and the natural outdoor conditions in the Negev desert. It is shown that all devices incorporating a Phenyl C61 Butyric Acid Methyl ester ([60]PCBM) layer undergo rapid degradation under illumination without exposure to oxygen and moisture. Time‐of‐flight secondary ion mass spectrometry depth profiling reveals that volatile products from the decomposition of methylammonium lead iodide (MAPbI3) films diffuse through the [60]PCBM layer, go all the way toward the top metal electrode, and induce its severe corrosion with the formation of an interfacial AgI layer. On the contrary, alternative electron‐transport material based on the perylendiimide derivative provides good isolation for the MAPbI3 films preventing their decomposition and resulting in significantly improved device operation stability. The obtained results strongly suggest that the current approach to design inverted perovskite solar cells should evolve with respect to the replacement of the commonly used fullerene‐based electron‐transport layers with other types of materials (e.g., functionalized perylene diimides). It is believed that these findings pave a way toward substantial improvements in the stability of the perovskite solar cells, which are essential for successful commercialization of this photovoltaic technology.

Direct Imaging of Current‐Induced Transformation of a Perovskite/Electrode Interface

“…The time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was applied to investigate the chemical composition of the perovskite between the electrodes and of the electrodes proper. The standard ToF‐SIMS technique yields the depth profiles of the target chemical species and is, hence, widely used for studying perovskite‐based solar cells, which are essentially the sandwich‐type (vertical) hybrid structures . However, the reliability of the ToF‐SIMS profiling data obtained on such structures is in doubt due to the atomic mixing induced by the ion beam damage and roughening of the interfaces during sputter or analysis cycles .…”

Molecular Engineering of the Fullerene‐Based Electron Transport Layer Materials for Improving Ambient Stability of Perovskite Solar Cells

“…Stability of PSCs strongly depends not only on the properties of photoactive layer but also on the proper selection of interfacial charge‐transport layers. Ideal hole transport (HTL) and electron transport (ETL) layers should be chemically inert with respect to the complex lead halides, have minimized energy level offsets with respect to the absorber material, enable efficient and selective extraction of charge carriers, and provide good isolation of perovskite layer, thus preventing its decomposition . There are many reports focused on the application of fullerenes and fullerene derivatives as ETLs for PSCs .…”

Molecular Aggregation of Naphthalene Diimide(NDI) Derivatives in Electron Transport Layers of Inverted Perovskite Solar Cells and Their Influence on the Device Performance

“…[13,24,25] Nevertheless, fullerenes possess constructional drawbacks such as easy absorption of oxygen or water onto the surfaceleading to degradation, poor morphological controllability under annealing conditions and difficult structural modification,m aking them far from ideal ETMs for inverted planarP SCs. [26][27][28] Thus, searching new alternatives is highly desirable.…”

“…Perylened iimide( PDI) [28][29][30] and naphthalene diimides (NDI) [31,32] have been widely employed as potentiall ow-temperaturep rocessed ETLs in inverted planar PSCs, due to the convenience of introducing functional groups, simplicity in synthesis and purification, tunable energy level alignmenta nd optoelectronic properties. [27,28,33] The advantages of PDI derivatives such as suppressing recombination losses, preventing decomposition and passivating the surfacet rap states of perovskite layer,h aveb een provenb yaseries of works. [34][35][36][37] NDIbased polymericE TLs such as P(NDI2OD-T2), P(NDI2DT-T2), P(NDI2OD-TT), P(NDI2DT-TTCN), PFN-2TNDI and PNVT-8 have also been widely studied due to the advantages of polymeric chain entanglement, lowest unoccupied molecular orbital (LUMO) energy level and the tunable hydrophobicity.…”