Poor light stability hinders the potential applications of perovskite optoelectronic devices. Recent experiments have demonstrated that the passivation surface via forming strong chemical bonds (SO4‐Pb, PO4‐Pb, Cl‐Pb, O‐Pb, and S‐Pb) could effectively improve the light stability of perovskite solar cells. However, the underlying reasons are not clear. Herein, the elusive underlying mechanisms of light stability enhancement are explained in detail using first principles calculations. The small polaron model and self‐trapped exciton model demonstrate that an iodine vacancy defect on the surface of perovskite could trap a free electron under light illumination, which leads to a significant rearrangement of the Pb–I lattice and creats a new chemical species, i.e., a Pb–Pb dimer bound in the typical perovskite of CH3NH3PbI3. The Pb–Pb dimer distorts the Pb–I octahedral lattice and reduces the defect formation energy of the I atoms. The surface Pb site passivation can prevent the formation of the Pb–Pb dimer, thereby improving the light stability. In addition, the strong ionic bond could better stabilize the Pb site. The in‐depth understanding of the light stability and the passivation mechanism in this study can promote the application of perovskite optoelectronic devices.
Perovskite solar cells (PSCs) are being developed rapidly and exhibit greatly potential commercialization. Herein, it is found that the device performance can be improved by manipulating the migration of iodine ions via reverse‐biasing, for example, at −0.4 V for 3 min in dark. Characterizations suggest that reverse bias can increase the charge recombination resistance, improve carrier transport, and enhance built‐in electric field. Iodine ions including iodine interstitials in perovskites are confirmed to migrate and accumulate at the SnO2/perovskite interface under reverse‐basing, which fill iodine vacancies at the interface and interact with SnO2. First‐principles calculations suggest that the SnO2/perovskite interface with less iodine vacancies has a stronger interaction and higher charge transfer, leading to larger built‐in electric field and improved charge transport. Iodine ions that may pass through the SnO2/perovskite interface are also confirmed to be able to interact with Sn4+ and passivate oxygen vacancies on the surface of SnO2. Consequently, an efficiency of 23.48% with the open‐circuit voltage (Voc) of 1.16 V is achieved for PSCs with reverse‐biasing, as compared with the initial efficiency of 22.13% with a Voc of 1.10 V. These results are of great significance to reveal the physics mechanism of PSCs under electric field.
Interfacial defects greatly influence the performance of perovskite solar cells (PSCs), and interface engineering is a powerful technique to promote the power conversion efficiency (PCE) of PSCs. Herein, an interfacial passivation strategy is developed employing cesium fluoride (CsF) to modify the surface of a perovskite film. Theoretical calculations suggest that the Cs+ and F− ions have a targeted passivation effect to decrease the defect density of the perovskite. Meanwhile, Cs+-formamidine+ (FA+) and F−–I− ion exchange can occur on the perovskite surface, which leads to the decline of the Fermi level of perovskite and reinforces the built-in potential of PSCs. Additionally, experiment results also confirm the reduction in the interfacial defects and the enhancement of the built-in potential. Consequently, the open-circuit voltage ( Voc) of PSCs is increased from 1.07 to 1.12 V, contributing to the promotion of the PCE. Furthermore, the stability of PSCs is obviously improved as well owing to the suppressed phase transition of α-phase perovskite. Our findings provide guidelines for surface modification of perovskite crystals to enhance the performance and stability of PSCs.
Perovskite solar cells (PSCs) have emerged as one of the most promising and competitive photovoltaic technologies, and doctor‐blading is a facile and robust deposition technique to efficiently fabricate PSCs in large scale, especially matching with roll‐to‐roll process. Herein, it demonstrates the encouraging results of one‐step, antisolvent‐free doctor‐bladed methylammonium lead iodide (CH3NH3PbI3, MAPbI3) PSCs under a wide range of humidity from 45% to 82%. A synergy strategy of ionic‐liquid methylammonium acetate (MAAc) and molecular phenylurea additives is developed to modulate the morphology and crystallization process of MAPbI3 perovskite film, leading to high‐quality MAPbI3 perovskite film with large‐size crystal, low defect density, and ultrasmooth surface. Impressive power conversion efficiency (PCE) of 20.34% is achieved for doctor‐bladed PSCs under the humidity over 80% with a device structure of ITO/SnO2/MAPbI3/Spiro‐OMeTAD/Ag. It is the highest PCEs for one‐step solution‐processed MAPbI3 PSCs without antisolvent assistance. The research provides a facile and robust large‐scale deposition technique to fabricate highly efficient and stable PSCs under a wide range of humidity, even with the humidity over 80%.
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