Formation and Diffusion of Metal Impurities in Perovskite Solar Cell Material CH₃NH₃PbI₃: Implications on Solar Cell Degradation and Choice of Electrode

Abstract

Solar cells based on methylammonium lead triiodide (MAPbI3) have shown remarkable progress in recent years and have demonstrated efficiencies greater than 20%. However, the long‐term stability of MAPbI3‐based solar cells has yet to be achieved. Besides the well‐known chemical and thermal instabilities, significant native ion migration in lead halide perovskites leads to current–voltage hysteresis and photoinduced phase segregation. Recently, it is further revealed that, despite having excellent chemical stability, the Au electrode can cause serious solar cell degradation due to Au diffusion into MAPbI3. In addition to Au, many other metals have been used as electrodes in MAPbI3 solar cells. However, how the external metal impurities introduced by electrodes affect the long‐term stability of MAPbI3 solar cells has rarely been studied. A comprehensive study of formation energetics and diffusion dynamics of a number of noble and transition metal impurities (Au, Ag, Cu, Cr, Mo, W, Co, Ni, Pd) in MAPbI3 based on first‐principles calculations is reported herein. The results uncover important general trends of impurity formation and diffusion in MAPbI3 and provide useful guidance for identifying the optimal metal electrodes that do not introduce electrically active impurity defects in MAPbI3 while having low resistivities and suitable work functions for carrier extraction.

First principles calculation of spin-related quantities for point defect qubit research

“…There are two main reasons for the improved performance of HSE06: (1) it exhibits a derivative discontinuity in the exchange correlation potential 80 that remedies the band gap underestimation problem of semilocal Kohn-Sham DFT functionals in conventional semiconductors 77,81 and (2) localized defect states often satisfy the generalized Koopman's theorem 78,82 thus there is no self-interaction for the auxiliary particles occupying the defect states. 83 We note that hybrid functionals may provide quantitatively less accurate [84][85][86] and even qualitatively incorrect results 85,87,88 for electronic structures of varying electron localization. It is well established that the exact exchange-semilocal exchange mixing parameters must be reconsidered when hybrid functionals are applied to semiconducting transition metal compounds.…”

Silver Iodide Induced Resistive Switching in CsPbI3 Perovskite‐Based Memory Device

“…Usually, inert metal electrodes only as a counter‐electrode or transport path contribute less to the resistive switching, while the active metal electrodes can be ionized and form conductive filaments through electrochemical reaction under voltage sweeps, playing an important role in resistive switching . Besides, some studies also have reported that the active electrode can react with the iodine ions in lead iodide perovskite to form metal iodide, such as AgI x , which the reaction require an external voltage, or only a condition of air exposure . This reaction not only causes the degradation of metal electrode, but also can generate more vacancies in perovskite film because of the formation of metal iodide reserving the iodine ions, which are always responsible for the I–V hysteresis.…”

Bias‐Dependent Stability of Perovskite Solar Cells Studied Using Natural and Concentrated Sunlight

“…We suggest the simultaneous presence of multiple degradation mechanisms at all degrading PSCs, with different mechanisms dominating at different bias conditions. Bias‐affected degradation mechanisms may include ion migration, either within the perovskite active layer, “intrinsic,” or between different cell layers, “extrinsic”; trap charging and discharging; and defect formation due to reactions involving accumulated charge carriers.…”