Relationship between ion migration and interfacial degradation of CH3NH3PbI3 perovskite solar cells under thermal conditions

Abstract

Organic-inorganic hybrid perovskite solar cells (PSCs) have been extensively studied because of their outstanding performance: a power conversion efficiency exceeding 22% has been achieved. The most commonly used PSCs consist of CH3NH3PbI3 (MAPbI3) with a hole-selective contact, such as 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spiro-bifluorene (spiro-OMeTAD), for collecting holes. From the perspective of long-term operation of solar cells, the cell performance and constituent layers (MAPbI3, spiro-OMeTAD, etc.) may be influenced by external conditions like temperature, light, etc. Herein, we report the effects of temperature on spiro-OMeTAD and the interface between MAPbI3 and spiro-OMeTAD in a solar cell. It was confirmed that, at high temperatures (85 °C), I− and CH3NH3 + (MA+) diffused into the spiro-OMeTAD layer in the form of CH3NH3I (MAI). The diffused I− ions prevented oxidation of spiro-OMeTAD, thereby degrading the electrical properties of spiro-OMeTAD. Since ion diffusion can occur during outdoor operation, the structural design of PSCs must be considered to achieve long-term stability.

Analysis of misidentifications in TEM characterisation of organic‐inorganic hybrid perovskite material

“…Moreover, it is also not rigorous to only measure one crystal plane to identify the phase, because the decomposed materials have approximate interplanar spacings with intrinsic perovskite. As shown in Figures 4(E)‐(H), 19,22,24,33 we completely cannot identify whether these materials are MAPbI 3 perovskite, PbI 2 , Pb or other intermediates based on one crystal plane. It generally seems to happen when the crystal is oriented in a way where lines are formed in the image due to tilting.…”

“…The widely existed misidentifications have negatively influenced the development of perovskite research field, such as structural determination, material growth, phase transition, heterostructure and so on 6,15–45 . Although the mistakes are being taken seriously, 14,46 analysing the causes of misidentifications, and proposing a solid method of phase identification for electron beam‐sensitive materials is still highly urgent.…”

Light capacitances in silicon and perovskite solar cells

“…It was early noted that even in the dark, PSCs shows relatively large capacitances (~50 µF cm -2 ) at low frequencies as compared with geometrical capacitance, irrespective of the perovskite bulk thickness (Almora et al, 2015). This fact indicated that interfaces between the absorbing semiconductor and contacting layers would be behind these uncommon capacitive experimental trends (Bergmann et al, 2016;Carrillo et al, 2016;Kim et al, 2017). Simultaneously, it was reported a hysteretic effect of the J-V curve under operation.…”

Plasma-Exposure-Induced Mobility Enhancement of LiTFSI-Doped Spiro-OMeTAD Hole Transport Layer in Perovskite Solar Cells and Its Impact on Device Performance

“…Chemical etching, also called plasma ashing, may remove organic matter and enlarge the size of nano-sized voids in spiro-OMeTAD HTL. The diffused negative ions from perovskite surface, such as I − into the voids in spiro-OMeTAD HTL may prevent oxidation of spiro-OMeTAD, and degrade the electric properties [30,31], which led to the “deterioration and recovery” behavior of spiro-OMeTAD HTL exposed to O 2 plasma.…”