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Title: Formation and Diffusion of Metal Impurities in Perovskite Solar Cell Material CH 3NH 3PbI 3 : Implications on Solar Cell Degradation and Choice of Electrode

Abstract

Solar cells based on methylammonium lead triiodide (MAPbI 3) have shown remarkable progress in recent years and have demonstrated efficiencies greater than 20%. However, the long-term stability of MAPbI 3-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 MAPbI 3. In addition to Au, many other metals have been used as electrodes in MAPbI 3 solar cells. However, how the external metal impurities introduced by electrodes affect the long-term stability of MAPbI 3 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 MAPbI 3 based on first-principles calculations is reported herein. The results uncover important general trends of impurity formation and diffusion in MAPbI 3 and provide useful guidance for identifying the optimal metal electrodes that do not introduce electrically active impurity defects in MAPbI 3 while havingmore » low resistivities and suitable work functions for carrier extraction.« less

Authors:
 [1];  [2];  [2];  [3]; ORCiD logo [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science & Technology Division
  2. Jilin Univ., Changchun (China). Key Lab. of Automobile Materials of MOE and Dept. of Materials Science and Engineering
  3. Jilin Univ., Changchun (China). Key Lab. of Automobile Materials of MOE and Dept. of Materials Science and Engineering; Jilin Univ., Changchun (China). State Key Lab. of Superhard Materials
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division; USDOE
OSTI Identifier:
1414958
Alternate Identifier(s):
OSTI ID: 1414959; OSTI ID: 1426589
Grant/Contract Number:
AC05-00OR22725; 2016YFB0201204; 61722403; 11404131; 11674121
Resource Type:
Journal Article: Published Article
Journal Name:
Advanced Science
Additional Journal Information:
Journal Volume: 5; Journal Issue: 2; Journal ID: ISSN 2198-3844
Publisher:
Wiley
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE

Citation Formats

Ming, Wenmei, Yang, Dongwen, Li, Tianshu, Zhang, Lijun, and Du, Mao-Hua. Formation and Diffusion of Metal Impurities in Perovskite Solar Cell Material CH3NH3PbI3 : Implications on Solar Cell Degradation and Choice of Electrode. United States: N. p., 2017. Web. doi:10.1002/advs.201700662.
Ming, Wenmei, Yang, Dongwen, Li, Tianshu, Zhang, Lijun, & Du, Mao-Hua. Formation and Diffusion of Metal Impurities in Perovskite Solar Cell Material CH3NH3PbI3 : Implications on Solar Cell Degradation and Choice of Electrode. United States. doi:10.1002/advs.201700662.
Ming, Wenmei, Yang, Dongwen, Li, Tianshu, Zhang, Lijun, and Du, Mao-Hua. Wed . "Formation and Diffusion of Metal Impurities in Perovskite Solar Cell Material CH3NH3PbI3 : Implications on Solar Cell Degradation and Choice of Electrode". United States. doi:10.1002/advs.201700662.
@article{osti_1414958,
title = {Formation and Diffusion of Metal Impurities in Perovskite Solar Cell Material CH3NH3PbI3 : Implications on Solar Cell Degradation and Choice of Electrode},
author = {Ming, Wenmei and Yang, Dongwen and Li, Tianshu and Zhang, Lijun and Du, Mao-Hua},
abstractNote = {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.},
doi = {10.1002/advs.201700662},
journal = {Advanced Science},
number = 2,
volume = 5,
place = {United States},
year = {Wed Dec 27 00:00:00 EST 2017},
month = {Wed Dec 27 00:00:00 EST 2017}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1002/advs.201700662

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  • Solar cells based on methylammonium lead triiodide (MAPbI 3) have shown remarkable progress in recent years and have demonstrated efficiencies greater than 20%. However, the long-term stability of MAPbI 3-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 MAPbI 3. In addition to Au, many other metals have been used as electrodes inmore » MAPbI 3 solar cells. However, how the external metal impurities introduced by electrodes affect the long-term stability of MAPbI 3 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 MAPbI 3 based on first-principles calculations is reported herein. The results uncover important general trends of impurity formation and diffusion in MAPbI 3 and provide useful guidance for identifying the optimal metal electrodes that do not introduce electrically active impurity defects in MAPbI 3 while having low resistivities and suitable work functions for carrier extraction.« less
  • CH 3NH 3PbI 3-based solar cells have shown remarkable progress in recent years but have also suffered from structural, electrical, and chemical instabilities related to the soft lattices and the chemistry of these halides. One of the instabilities is ion migration, which may cause current–voltage hysteresis in CH 3NH 3PbI 3 solar cells. Significant ion diffusion and ionic conductivity in CH 3NH 3PbI 3 have been reported; their nature, however, remain controversial. In the literature, the use of different experimental techniques leads to the observation of different diffusing ions (either iodine or CH 3NH 3 ion); the calculated diffusion barriersmore » for native defects scatter in a wide range; the calculated defect formation energies also differ qualitatively. These controversies hinder the understanding and the control of the ion migration in CH 3NH 3PbI 3. In this paper, we show density functional theory calculations of both the diffusion barriers and the formation energies for native defects (V I +, MA i +, V MA , and I i ) and the Au impurity in CH 3NH 3PbI 3. V I + is found to be the dominant diffusing defect due to its low formation energy and the low diffusion barrier. I i and MA i + also have low diffusion barriers but their formation energies are relatively high. The hopping rate of V I + is further calculated taking into account the contribution of the vibrational entropy, confirming V I + as a fast diffuser. We discuss approaches for managing defect population and migration and suggest that chemically modifying surfaces, interfaces, and grain boundaries may be effective in controlling the population of the iodine vacancy and the device polarization. We further show that the formation energy and the diffusion barrier of Au interstitial in CH 3NH 3PbI 3 are both low. As a result, it is thus possible that Au can diffuse into CH3NH3PbI3 under bias in devices (e.g., solar cell, photodetector) with Au/CH 3NH 3PbI 3 interfaces and modify the electronic properties of CH 3NH 3PbI 3.« less
  • CH 3NH 3PbI 3-based solar cells have shown remarkable progress in recent years but have also suffered from structural, electrical, and chemical instabilities related to the soft lattices and the chemistry of these halides. One of the instabilities is ion migration, which may cause current–voltage hysteresis in CH 3NH 3PbI 3 solar cells. Significant ion diffusion and ionic conductivity in CH 3NH 3PbI 3 have been reported; their nature, however, remain controversial. In the literature, the use of different experimental techniques leads to the observation of different diffusing ions (either iodine or CH 3NH 3 ion); the calculated diffusion barriersmore » for native defects scatter in a wide range; the calculated defect formation energies also differ qualitatively. These controversies hinder the understanding and the control of the ion migration in CH 3NH 3PbI 3. In this paper, we show density functional theory calculations of both the diffusion barriers and the formation energies for native defects (V I +, MA i +, V MA , and I i ) and the Au impurity in CH 3NH 3PbI 3. V I + is found to be the dominant diffusing defect due to its low formation energy and the low diffusion barrier. I i and MA i + also have low diffusion barriers but their formation energies are relatively high. The hopping rate of V I + is further calculated taking into account the contribution of the vibrational entropy, confirming V I + as a fast diffuser. We discuss approaches for managing defect population and migration and suggest that chemically modifying surfaces, interfaces, and grain boundaries may be effective in controlling the population of the iodine vacancy and the device polarization. We further show that the formation energy and the diffusion barrier of Au interstitial in CH 3NH 3PbI 3 are both low. As a result, it is thus possible that Au can diffuse into CH3NH3PbI3 under bias in devices (e.g., solar cell, photodetector) with Au/CH 3NH 3PbI 3 interfaces and modify the electronic properties of CH 3NH 3PbI 3.« less
  • Methylammonium (MA) lead triiodide (MAPbI 3) has recently emerged as a promising solar cell material. But, MAPbI3 is known to have chemical instability, i.e., MAPbI3 is prone to decomposition into MAI and PbI 2 even at moderate temperatures (e.g. 330 K). Here, we show that the chemical instability, as reflected by the calculated negligible enthalpy of formation of MAPbI 3 (with respect to MAI and PbI 2), has an unusual and important consequence for defect properties, i.e., defect formation energies in low-carrier-density MAPbI 3 are nearly independent of the chemical potentials of constituent elements and thus can be uniquely determined. This allows straightforward calculations of defect concentrations and the activation energy of ionic conductivity (the sum of the formation energy and the diffusion barrier of the charged mobile defect) in MAPbI 3. Furthermore, the calculated activation energy for ionic conductivity due to Vmore » $$+\atop{1}$$ diffusion is in excellent agreement with the experimental values, which demonstrates unambiguously that V$$+\atop{1}$$ is the dominant diffusing defect and is responsible for the observed ion migration and device polarization in MAPbI3 solar cells. The calculated low formation energy of a Frenkel pair (V$$+\atop{1}$$ -I$$-\atop{i}$$ and low diffusion barriers of V$$+\atop{1}$$ and Image I$$-\atop{i}$$ suggest that the iodine ion migration and the resulting device polarization may occur even in single-crystal devices and grain-boundary-passivated polycrystalline thin film devices (which were previously suggested to be free from ion-migration-induced device polarization), leading to device degradation. Moreover, the device polarization due to the Frenkel pair (which has a relatively low concentration) may take a long time to develop and thus may avoid the appearance of the current–voltage hysteresis at typical scan rates.« less