Effect of Pressing Pressure on the Performance of Perovskite Solar Cells

Metal halide perovskite solar cells (PSCs) have undergone remarkably rapid progress with their power conversion efficiency (PCE) increasing from 3.8% to 23.7% in merely 9 years. Although an enormous research effort has been devoted to performance improvement, there has been little investigation of the effect of postfabrication processes such as encapsulation or packaging on device PCE. In this work, the effect of pressing on the performance of mesoporous PSCs is studied. Cells with the state-of-the-art architecture glass/FTO/c-TiO2/mp-TiO2/perovskite/spiro-OMeTAD/gold are used in this study. It is found that pressing under the condition typically used for encapsulation is beneficial for these PSCs, improving their PCE consistently by more than 7% relative on average. The effect of pressing was characterized by light current density- voltage measurement (LJV) time-resolved photoluminescence (TR-PL), X-ray diffraction (XRD), and electrical impedance spectroscopy (EIS). The PCE enhancement is due to an improved interface resulting in a higher fill factor, lower recombination, and lower hysteresis. It is found that pressing pressure of 400-500 mbar is appropriate; higher pressure at 1000 mbar is detrimental. Moreover, pressure must be maintained to maintain the PCE improvement. Pressing is an essential part of an encapsulation process, and this work demonstrates the beneficial effect of pressing on PSCs, inspiring future development of encapsulation and packaging.