Relationship between ion migration and interfacial degradation of CH(3)NH(3)PbI(3) perovskite solar cells under thermal conditions

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 CH(3)NH(3)PbI(3) (MAPbI(3)) 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 (MAPbI(3), 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 MAPbI(3) and spiro-OMeTAD in a solar cell. It was confirmed that, at high temperatures (85 °C), I(−) and CH(3)NH(3) (+) (MA(+)) diffused into the spiro-OMeTAD layer in the form of CH(3)NH(3)I (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.