Influence of hydration water on CH_3NH_3PbI_3 perovskite films prepared through one-step procedure

Abstract

Organic-inorganic perovskites were fabricated through a one-step procedure with different levels of hydration water in precursor solutions. The optical properties of CH₃NH₃PbI₃ films were investigated through spectroscopic ellipsometry and photoluminescence measurements. With the measured optical constants, the efficiency limit of perovskite solar cells is predicted with a detailed balance model. By comparing the optical measurement to that of planar heterojunction solar cells, we conclude that the radiative efficiency and porosity of the perovskite film significantly influence the performance of perovskite solar cells. An optimized hydration-water concentration is obtained for the 3CH₃NH₃I:1PbAc₂•xH₂O precursor solution. The results can provide guidance for further optimization of the device performance of perovskite solar cells by utilizing hydration water.

Impact of H2O on organic–inorganic hybrid perovskite solar cells

“…33 Following this work, further study demonstrated the optimized ratio 3MAI : 1Pb(Ac) 2 Á1.5H 2 O, ascribed to the trade-off of reducing the non-radiative pathway and increasing porosity. 34 Similarly, the water of hydrate MAI, although it does not impact coverage, also lead to improved performance of PSCs by significantly enhancing the lifetime of excited carriers in the MAPbI 3 layer. 31…”

Ambient Fabrication of Organic–Inorganic Hybrid Perovskite Solar Cells

“…These findings can also be confirmed by the higher photoluminescence, the longer lifetime and the increased open circuit voltage (V oc ) of the perovskite films formed under moisture exposure, due to reduced defects and suppressed recombination. [95,100,102] Moisture showed a healing effect on the perovskite film due to the partial hydration from water molecules. [95,103] Water in the atmosphere can solubilize and mobilize excess methylammonium, accelerate its removal from the perovskite film, and thus reducing the trap state density and enhancing the performance.…”

“…Benefits of Water: Interestingly, the addition of water or the use of hydrated lead precursors has been reported to have beneficial effects on the formation of the perovskite film and thus resulted in improved device performance. [102,104] Gong et al [104] found that trace amounts of water (2%) in DMF can improve the high vapor pressure and lower the boiling point. [104] Similarly, He et al [105] fabricated PSCs with water (1.5%) added in the DMF precursor solution under 40% RH.…”

“…It was found that a hydration water concentration of x = 1.5 for 3CH 3 NH 3 I:1PbAc 2 •xH 2 O was considered to be the optimal precursor, providing the lowest surface roughness, highest photocurrent and good balance between nonradiative recombination pathways and surface porosity. [102] Figure 5. a) The spin-coating and WVA method. b) The mechanism of WVA method showing the crystal growth processes in the perovskite film; 1) absorption of water on the perovskite surface forming strong hydrogen bonds between MA cations and the Pb-I cage; 2) hydrolysis of the perovskite into PbI 2 and CH 3 NH 3 I; 3) once the water evaporates, CH 3 NH 3 I and PbI 2 react to reform the perovskite.…”

Optical Properties of Al-Doped ZnO Films in the Infrared Region and Their Absorption Applications

“…Then, the refractive index n , extinction coefficient k and thickness d of the resulting AZO thin films were obtained by the SE measurement. During the SE measurement [ 25 , 26 ], the elliptically polarized light, carrying the material’s information after reflected by AZO films, was detected by the ellipsometer. The wavelength of the incident light was within the range of 210–5000 nm.…”