Study on the stability of the mixed (MAPbI3 and MAPbBr3) perovskite solar cells using dopant-free HTL

This study sheds a light on the instability and degradation factors occurring within the dopant-free hole transport layer (HTL) based perovskite solar cells with aging time. To prepare the perovskite solar cells (PSCs), a layer-by-layer deposition method was adopted. The PSCs were prepared in the conventional n-i-p structure using the mixed perovskite (MAPbI(3) and MAPbBr(3)) solution. FA-CN based dopant-free HTL was deposited on the top of the perovskite layer using the spin coating procedure. The fresh and aged (for 45, 90 and 180 days) PSCs were studied by using current-voltage (I-V) characterization technique and impedance spectroscopy (IS). The average power conversion efficiency (PCE) of the freshly prepared PSCs was similar to 15.98%. With the aging, the hysteresis in the I-V characteristics was increased and a noticeable rise in the deep traps has been noted. IS spectra demonstrates that charge transfer resistance of the samples was reduced with the passage of time, which indicates that the compact-TiO2 layer (blocking layer) might be degraded and the electrical properties of the FTO/TiO2/ perovskite interfaces have been effected. Furthermore, the recombination resistance of the samples has also been decreased significantly during the aging process. Based on the experimental results, fundamental features that account for the instability in the perovskite solar cells have been discussed.