Unraveling the hidden function of a stabilizer in a precursor in improving hybrid perovskite film morphology for high efficiency solar cells

Abstract

The precursor purity is critical for the perovskite film morphology and solar cell device performance.

Additive‐Assisted Crystallization Dynamics in Two‐Step Fabrication of Perovskite Solar Cells

“…On the other hand, too high concentrations cause degradation, which is more pronounced for thinner layers. These observations are consistent with the results presented by Zhang et al and Xiao et al, where HPA also improved the layer quality in case of a one‐step process based on lead acetate and lead iodide. This is an important observation because it can narrow down the still not completely understood mechanism of HPA directly to a chemical interaction between the lead precursor and the methylammonium iodide during perovskite formation.…”

“…Zhang et al assumed that HPA acts as a reducing agent, preventing the reaction of methylammonium iodide to methylammonium and elementary iodine, which would cause a deficit between the reagents and thus hamper a smooth film formation. Xiao et al, however, reported a reaction between the phosphoric compound and the other reagents forming new precursor compounds like CH 3 NH 3 (H 2 PO 2 ) and Pb(H 2 PO 2 ) 2 that are able to slow down the reaction with the result of an improved layer quality. Recently, another group claimed that the addition of HPA in a mixed methylammonium iodide and lead iodide solution for the one‐step process forms colloidal structures made of PbHPO 3 , promoting the formation of larger grains by acting as crystallization source .…”

“…In order to improve grain size and layer morphology, crystallization dynamics of CH 3 NH 3 PbI 3 are controlled by adding non‐toxic hypophosphorous acid (HPA) into the methylammonium iodide/isopropanol solution. A similar use of HPA with excellent improvements in layer quality has already been described by Zhang et al and by Xiao et al for the one‐step process based on lead acetate and lead iodide, respectively. The sequence of thermal evaporation and solution‐based method introduced here combines the excellent thickness control, uniformity, and reproducibility of a vacuum processing with the ease of fabrication and controllability of crystallization in a solution‐based process.…”

Μethylammonium Chloride: A Key Additive for Highly Efficient, Stable, and Up‐Scalable Perovskite Solar Cells

“…[72] Very similar results with lower trap density upon MACl addition in MAPbI 3 perovskites were drawn from space-charge-limited current or impedance spectroscopy measurements. [64,65,72,76] Remarkably, MAH 2 PO 2 -only additive, which is the product of the reaction of H 3 PO 2 with methylamine, [77] already presented a lower density of defects at grain boundaries in comparison with MACl. [64,65,72,76] Remarkably, MAH 2 PO 2 -only additive, which is the product of the reaction of H 3 PO 2 with methylamine, [77] already presented a lower density of defects at grain boundaries in comparison with MACl.…”

Exploration of fabrication methods for planar CH3NH3PbI3 perovskite solar cells

“…[7] Although these research efforts have advanced PeSCs, there are still a number of open questions: toxicity, [18] the stability, [19] reliability, uncertainty in the measurement of efficiency (hysteresis, overestimation), [20][21][22][23] the choice of interfacial layer, [3] crystallinity (preferred vs non-preferred orientation, [24][25][26] big vs small grain size [27,28]), and structural device (planar vs mesoporous, [29] inverted vs normal [30,31]). Considering the sensitivity and instability of perovskites under ambient condition, it is actually difficult to reproduce the result of PeSCs fabricated by many research groups [32] and trust their results because conditions between laboratories are significantly different and some papers may include selectively picked data for showing record efficiency.…”