Perspective: Understanding of ripening growth model for minimum residual PbI2 and its limitation in the planar perovskite solar cells

Abstract

The power conversion efficiency of lead halide perovskite solar cells recently surpassed 22.1%. In this study, we suggest the perovskite absorber growth mechanism of the two-step process could be explained by an Ostwald ripening growth model for planar-structure perovskite solar cells. We attempt to find out the source of two main problems such as unreacted PbI2 and non-uniformed morphology by the proposed ripening growth mechanism and experimental results. This growth mechanism opens the way toward understanding a key aspect of the photovoltaic operation of high-efficiency, two-step perovskite solar cells.

Perovskite Solar Cells Prepared by Advanced Three-Step Method Using Additional HC(NH2)2I Spin-Coating: Efficiency Improvement with Multiple Bandgap Structure

“…The unreacted PbI2 (thickness of several tens nanometer) is reported to exist mainly at the interface between ETL and perovskite active layer. 23 The additional FAI spin-coating converted MAPbI3…”

Transferrable optimization of spray-coated PbI2 films for perovskite solar cell fabrication

“…Ko et al 10 implemented a 2-step perovskite formation process under ambient conditions and found that optimal performance was obtained with PbI 2 peak in the XRD pattern around 50% as high as MAPbI 3 peak. Kim et al 17 discussed in detail the formation process of the MAPbI 3 in a 2-step process, and concluded that excess PbI 2 cannot be eliminated by simple optimization of MAI solution concentration and immersion time, without compromising the performance. On the other hand, it is expected that further enhancement of MAPbI 3 crystallinity can lead to increased performance.…”

Perovskite solar cells prepared by a new 3-step method including a PbI 2 scavenging step

“…The microstructure development is attributable to the dissolution of perovskite particles at the surface into the additionally spincoated CH3NH3X solution. It is reported that the CH3NH3PbI3 particle growth in the 2-step method is due to the dissolution of the small particles in CH3NH3X solution and redeposition on the larger particles (Ostwald ripening growth) as a following reaction [21,24]:…”

“…The residual PbI2 can be decreased by (i) prolonging the dipping time in the CH3NH3I solution and (ii) increasing the concentration of the CH3NH3X solution. However, the performance of perovskite solar cells often decreased with those methods due to (i) the damage to the CH3NH3PbI3 particles by the solvent and (ii) the decrease of CH3NH3PbI3 particle size, respectively [17,21,22].…”