Homeopathic Perovskite Solar Cells: Effect of Humidity during Fabrication on the Performance and Stability of the Device

Abstract

Methylammonium Lead Iodide (CH 3 NH 3 PbI 3 ) is the archetypical active component of perovskite solar cells, which stand out due to their impressive photovoltaic performance. A major drawback of CH 3 NH 3 PbI 3 is its rapid degradation in humid environments.In this work, we fabricate CH 3 NH 3 PbI 3 films and devices by solvent engineering in N 2 and in ambient conditions with different humidities. Their aging and degradation is monitored by optical absorption and impedance spectroscopy measurements under monochromatic illumination with two different wavelengths. Aged devices show a substantial difference between the recombination rate under red and blue light illumination, attributed to enhancement of local recombination routes upon aging. Interestingly, we observe that devices prepared at higher humidity resist better the aging. We explain this by the presence of coordinating water in the films, as detected by XPS measurements. Hence, small amounts of water in the perovskite structure proves to have a beneficial effect against degradation in humid environments.

Stability of Cubic FAPbI3 from X-ray Diffraction, Anelastic, and Dielectric Measurements

“…This is especially true in the cases of intentional exposure to moisture during preparation in order to improve the grain morphology through solvent annealing. 38,39 Acknowledgement The authors thank Paolo Massimiliano Latino (ISM-Tor Vergata) for his technical assistance, Sara Notarantonio (ISM-Montelibretti) for the assistance in the synthesis, Marco Guaragno (ISM-Tor Vergata) for his technical support in X-ray experiments, Dr. Cristina Riccucci for the DTA-DSC measurements and Dr. Gloria Zanotti for fruitful discussions.…”

Crystalline Clear or Not: Beneficial and Harmful Effects of Water in Perovskite Solar Cells

“…[50] More recently, an interesting additive-antisolvent method under room conditions has been proposed by Yang et.al. [18,53] They found that perovskite prepared under higher %RH presents more robust resistance to degradation, attributing this robustness to the retained water molecules into the perovskite structure, which avoid further invasion of moisture (Figure 4d). They proposed an enhanced crystallinity lacking of pinholes and reduced hysteretic behaviour in devices prepared with their method, attributing this effect to a fast extraction of water molecules during the annealing step, as methanol has high water solubility.…”

“…At a similar conclusions arrived Contreras et.al analysing recently the effects of moisture during MAPbI 3 preparation. [18,53] They found that perovskite prepared under higher %RH presents more robust resistance to degradation, attributing this robustness to the retained water molecules into the perovskite structure, which avoid further invasion of moisture ( Figure 4d).…”

“…[15] At this stage, the presence of water can be catalogued as a beneficial factor, helping in the crystallization process of perovskite material and performing increased grain size. [17,18] However, if the equilibrium is displaced to the right (red) due to an increased amount of water, the dihydrated phase governs the situation. [17,18] However, if the equilibrium is displaced to the right (red) due to an increased amount of water, the dihydrated phase governs the situation.…”

“…[16] A high crystalline lattice perovskite material also induces an improvement in photocurrent, photoluminescence, photovoltage and even in the stability of the perovskite devices, avoiding the inclusion of more water molecules into the structure. [17,18] However, if the equilibrium is displaced to the right (red) due to an increased amount of water, the dihydrated phase governs the situation. From a morphological point of view, water begins to collapse the grain boundaries of perovskite film, broken their interconnectivity and fabricating isolating trails that increase the recombination pathways.…”