Stabilizing black-phase formamidinium perovskite formation at room temperature and high humidity

Abstract

The stabilization of black-phase formamidinium lead iodide (α-FAPbI3) perovskite under various environmental conditions is considered necessary for solar cells. However, challenges remain regarding the temperature sensitivity of α-FAPbI3 and the requirements for strict humidity control in its processing. Here we report the synthesis of stable α-FAPbI3, regardless of humidity and temperature, based on a vertically aligned lead iodide thin film grown from an ionic liquid, methylamine formate. The vertically grown structure has numerous nanometer-scale ion channels that facilitate the permeation of formamidinium iodide into the lead iodide thin films for fast and robust transformation to α-FAPbI3. A solar cell with a power-conversion efficiency of 24.1% was achieved. The unencapsulated cells retain 80 and 90% of their initial efficiencies for 500 hours at 85°C and continuous light stress, respectively.

Germanium-lead perovskite light-emitting diodes

“…3f). The efficiency improvement may be attributed to the reduced trap density (estimated hole trap density: 1.06 × 10 18 cm −3 , electron trap density: 5.72 × 10 17 cm −3 ) of the Ge-Pb PeLEDs with 10 mol% Ge compared to the control devices (hole trap density: 1.11 × 10 18 cm −3 , electron trap density: 8.06 × 10 17 cm −3 ), as suggested by space-charge-limited current (SCLC) analysis 38,39 (Supplementary Figs. 11a, b and 12a, b).…”

“…The luminance (in cd m −2 ) of the devices was calculated based on the emission function of the PeLED and on the known spectral response of the charge-coupled device, and the EQEs of the devices were calculated assuming a Lambertian emission profile. In order to determine the trap density of Ge–Pb perovskite films prepared with different Ge substitutions, we carried out space charge limited current (SCLC) analysis using the equation 38 , 39 : , where is the vacuum permittivity, is the relative permittivity of perovskite, V TEF is the trap-filled-limit voltage, e is the elementary charge, and L is the thickness of the thin film. The film thickness (from HAADF-STEM studies) and relative permittivity of all Ge–Pb perovskite films were estimated to be 50 nm and 29.37 43 , respectively.…”

Structural Transitions and Stability of FAPbI3 and MAPbI3: The Role of Interstitial Water

“…There are several studies that report beneficial effects of moisture on the crystal morphology and perfection, which finally result in improvements of the photovoltaic efficiency and stability of the devices [ 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 66 , 82 , 83 ]. These effects are generally attributed to liquid phases that promote the dissolution and recrystallization of the grains [ 31 , 36 , 66 ], but in view of the conclusions reached here on interstitial water, we suggest that also the latter plays a role.…”

“…A positive role of humidity has also been found in the otherwise dry mechanosynthesis of MAPI, where it catalyzes the reaction between MAI and PbI [ 87 ]. It seems therefore promising to study crystallization processes in presence of controlled amounts of water or humidity, especially in combination with in situ monitoring of the crystallization process, as with GIWAX [ 39 , 56 , 57 ] or optical reflectance [ 88 ].…”

“…Much attention has been devoted to the degradation induced by humidity [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ], but much less to the catalytic effects of intercalated water molecules on crystallization and polymorphism [ 19 ]. Actually, beneficial effects of moisture on the crystal morphology and perfection, resulting in improved photovoltaic efficiency and stability, have been often reported [ 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ], but remain generally unexplained.…”