Researchers from The Hebrew University of Jerusalem and Ben-Gurion University of the Negev in Israel, have studied the two-step deposition of perovskites in mesoporous-carbon-based perovskite solar cells. The team studied the effect of the different deposition parameters on the PV performance and stability.
b) Schematic illustration of the two-step deposition process. The first stage includes dropping of the PbI2 þ PbBr2 solution, the second step includes dipping into the cation solution of FAI þ MABr. Image from article
The influence of the dipping time on the photovoltaic parameters was investigated using charge extraction and intensity-modulated photovoltage spectroscopy (IMVS) measurements. By modifying the perovskite precursors' concentration and the dipping time, a PCE of 15% was achieved. The dipping time in the perovskite deposition of this solar cell structure is critical due to its thickness and mesoporous structure.
The team has found that stability characterizations at maximum power point (MPP) tracking showed degradation with time, however a complete recovery of the devices in the dark was revealed. Analyzing the mechanism for this showed that the perovskite's unit cell shrinks during the recovery process due to internal stress relief. The close proximity of the perovskite's components within the mesoporous carbon structure assist the recovery process in this case, as was observed by XRD measurements.
The team proposes that partial perovskite decomposition and recrystallization occur within the carbon electrode pores during light exposure and subsequent dark recovery, respectively, relieving internal stresses in the perovskite. As internal stresses are known to negatively affect PSC stability, such degradation-recovery cycles inducing stress relief may contribute to improved device operational stability. This interesting phenomenon could open the door to optimizing the stability of such solar cells for commercial applications.
MA0.15FA0.85Pb(I0.85Br0.15)3 perovskite was used for this study (FA- formamidinium, MA-methyl ammonium), as it is one of the compositions that show high PV performance in perovskite solar cells.
