Electrical properties and J-V modeling of perovskite (CH3NH3PbI3) solar cells after external thermal exposure

In this work, the effects of external temperature exposure on perovskite solar cells are reported. Experimental solar cells, with the configuration FTO/c-TiO2/m-TiO2/CH3NH3PbI3/Spiro-OMETAD/Au, were fabricated and exposed to different external temperatures (25, 40, 60 and 70 degrees C) for four hours. The objective was to compare the effects of external temperature exposure on perovskite solar cells. The thin films were characterized using SEM, XRD and absorption spectra. The solar cells were characterized obtaining their J-V curves, and using curve simulations to quantify changes in the working mechanisms of the cells. Experimental results indicate that samples exposed to temperatures under 40 degrees C suffer a decrease in PCE, mainly due to a reduction in FF but deaden by an increase in J(sc). In addition, when the samples are exposed to higher temperatures, there is a general decrease in all photovoltaic parameters resulting in a considerable reduction in PCE. Simulations indicate that degradation of the cells starts at ambient temperature with the dissolution of the perovskite to form PbI2 which introduces trap levels which reduce the FF. However, if the temperature is kept below 40 degrees C, the perovskite film can recrystallize inducing grain coalescence which reduces leakage and improves conductivity. This in turn produces an increase of J(sc) and a reduction of FF decay. Thus, decreasing lost performance and preserving about 80% of the original efficiency. On the other hand, if the cell is exposed to a temperature above 40 degrees C, the degradation processes accelerate, recrystallization becomes disordered resulting in the formation of pinholes and defects. These defects, coupled with a higher amount of PbI2, will result in reduction of J(sc), V-oc and FF, reducing the PCE.

Automated summary

The study reports the effects of external temperature exposure on perovskite solar cells. Results show that exposure to temperatures below 40 degrees Celsius leads to a decrease in performance mainly due to a reduction in fill factor, while exposure to higher temperatures results in a general decrease in all photovoltaic parameters and a significant reduction in power conversion efficiency.