Supporting Information Abnormal Current-Voltage Hysteresis Induced ...
Supporting Information Abnormal Current-Voltage Hysteresis Induced by Reverse Bias in Organic-Inorganic Hybrid Perovskite Photovoltaics Adharsh Rajagopal, Spencer T. Williams, Chu-Chen Chueh, and Alex K-Y. Jen*
Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, United States *Address correspondence to: [email protected]
Breakdown mechanisms Breakdown of a p-n junction refers to the phenomenon where sufficiently high electric field due to applied voltage in reverse bias (RB) regime breaks down the junction and results in large current. The key characteristics of common breakdown mechanisms are as follows:1,2 (1) Thermal instability: In p-n junctions with large reverse saturation current, the power dissipated due to increased reverse current raises the junction temperature, consequently initiating the breakdown and destruction of the diode. The impact of breakdown due to thermal instability is irreversible. (2) Tunneling: In heavily doped p-n junctions, under large electric field in reverse bias, the carriers can tunnel through the narrow depletion region and result in Zener breakdown. This mechanism is responsible for the breakdown in a tunnel diode, with threshold voltage typically shifted to 0 V. Further, in a tunnel diode, non-linear current-voltage relationship and negative resistance (NR) region observed in the forward bias is associated with tunneling. (3) Avalanche multiplication: In p-n junctions, under high enough electric field in depletion region, electron-hole pairs are generated by impact ionization process and result in Avalanche breakdown. This mechanism of breakdown is observed at larger reverse bias (RB) compared to Zener breakdown.
Generally, Avalanche and Zener breakdown do not leave an irreversible impact on the diode, unless an excessively large reverse current increases the power dissipated and burns out the device due to raise in temperature. The “knee” of these breakdown are considerably sharper than the current rise in forward direction. With the use of series-limiting resistor, diode can be utilized under breakdown conditions as a voltage stabilizer or switch.
Figure S1. Bi-exponential fit of stabilized current measured under illumination at maximum power point obtained from I-V measurements of CH3NH3PbI3 based solar cells with PEDOT:PSS and Cu:NiOx HTLs.
Figure S2. I-V scans for PEDOT:PSS based devices measured with longer delay time (1000 ms), corresponding to a scan rate of 0.01 V/s.
Figure S3. Standalone FBRB (reverse) I-V scans starting at +1.2 V (FB) and ending at different points in reverse bias (RB), indicating anomalous breakdown in CH3NH3PbI3 based solar cells with Cu:NiOx HTL.
Figure S4. Correlation between the stabilized current under illumination at (a) -0.1 V and (b) 0.2 V with corresponding values from RBFB (forward) I-V scan for CH3NH3PbI3 based solar cells with Cu:NiOx HTL.
Figure S5. Variation of the FB inflection in RBFB I-V scans (-0.2 V to 1.1 V) measured at different delay times for CH3NH3PbI3 based solar cells with Cu:NiOx HTL; 100 ms , 1000 ms and 3000 ms delay times correspond to scan rates 0.1 V/s, 0.01 V/s and 0.003 V/s respectively; inset shows the zoomed in region of FBRB scans.
Figure S6. CH3NH3PbI3 based solar cells with Cu:NiOx/PEDOT:PSS dual HTL. (a) Device structure. (b) I-V behavior for scans starting at 0 V, -0.5 V and -1 V. (c) Bi-exponential fit of stabilized current under illumination at maximum power point. (d) Statistical data of photovoltaic performance metrics.
Figure S7. Comparison of RBFB (forward) and FBRB (reverse) I-V scans under illumination for CH3NH3PbI3 based solar cells with NiOx HTL, starting at 0 V and different points in reverse bias (RB).
Figure S8. SEM and AFM morphologies of (a) & (d) ITO glass; (b) & (e) PEDOT:PSS spin coated on ITO glass; (c) & (f) NiOx spin coated on ITO glass, respectively. The calculated RMS value of roughness (RRMS) for different surfaces is specified below their corresponding AFM images. Scan parameters were kept unaltered during measurement of different surfaces; scale bars in SEM and AFM images denote 500 nm and 1 µm respectively.
Figure S9. Dependence of abnormal I-V behavior on light (1 Sun illumination) soaking at (a) short circuit, SC (Vext = 0 V) and (b) reverse bias, RB (Vext = -0.2 V) for CH3NH3PbI3 based solar cells with Cu:NiOx HTL.
Figure S10. Normalized EQE at different RB, showing consistency of spectral shape for CH3NH3PbI3 based solar cells with Cu:NiOx HTL.
Figure S11. Hypothesis for HTL dependent I-V behavior in CH3NH3PbI3 based solar cells. The electric field due to applied external reverse bias (Eext) coupled with built-in electric field (Ebi) would induce accumulation of positive and negative point defects at HTL/CH3NH3PbI3 and ETL/CH3NH3PbI3 interfaces respectively.3 Recently reported interactions4 between PEDOT:PSS and CH3NH3PbI3 could possibly relieve ion accumulation at the PEDOT:PSS/CH3NH3PbI3 interface. However, non-interacting nature of metal oxides could withhold ion accumulation5–7 near HTL and subsequently induce a compensating electric field3,8,9 (Ecomp) and accompanying doping of CH3NH3PbI3 in proximity to NiOx, ultimately responsible for the observed tunnel junction behavior; the direction of Ecomp counteracts Ebi and Eext in RB. The curved arrow at ETL/CH3NH3PbI3 interfaces highlight the possibility of I-/PCBM interaction as demonstrated recently.10
Table S1. Photovoltaic performance metrics calculated from standard I-V scans (0 V to 1.1 V, 100 ms delay time) measured after different device pre-conditioning; numbers 1-5 refer to the order of measurement.
References (1) (2) (3) (4)
(5) (6) (7)
(8)
(9)
(10)
Solymar, L.; Walsh, D. Electrical Properties of Materials, 8th ed.; Oxford University Press: Oxford, 2010. Sze, S. M.; Ng, K. K. Physics of Semiconductor Devices, 3rd ed.; John Wiley & Sons: New Jersey, 2006. Eames, C.; Frost, J. M.; Barnes, P. R. F.; O’Regan, B. C.; Walsh, A.; Islam, M. S. Ionic Transport in Hybrid Lead Iodide Perovskite Solar Cells. Nat. Commun. 2015, 6, 7497. Xia, Y.; Sun, K.; Chang, J.; Ouyang, J. Effects of Organic Inorganic Hybrid Perovskite Materials on the Electronic Properties and Morphology of poly(3,4Ethylenedioxythiophene):poly(styrenesulfonate) and the Photovoltaic Performance of Planar Perovskite Solar Cells. J. Mater. Chem. A 2015, 3, 15897–15904. Almora, O.; Guerrero, A.; Garcia-Belmonte, G. Ionic Charging by Local Imbalance at Interfaces in Hybrid Lead Halide Perovskites. Appl. Phys. Lett. 2016, 108, 043903. Li, L.; Wang, F.; Wu, X.; Yu, H.; Zhou, S.; Zhao, N. Carrier-Activated Polarization in Organometal Halide Perovskites. J. Phys. Chem. C 2016, 120, 2536–2541. Zarazua, I.; Bisquert, J.; Garcia-Belmonte, G. Light-Induced Space-Charge Accumulation Zone as Photovoltaic Mechanism in Perovskite Solar Cells. J. Phys. Chem. Lett. 2016, 7, 525–528. Tress, W.; Marinova, N.; Moehl, T.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; Grätzel, M. Understanding the Rate-Dependent J–V Hysteresis, Slow Time Component, and Aging in CH3NH3PbI3 Perovskite Solar Cells: The Role of a Compensated Electric Field. Energy Environ. Sci. 2015, 8, 995–1004. Zhao, C.; Chen, B.; Qiao, X.; Luan, L.; Lu, K.; Hu, B. Revealing Underlying Processes Involved in Light Soaking Effects and Hysteresis Phenomena in Perovskite Solar Cells. Adv. Energy Mater. 2015, 5, 1500279. De Bastiani, M.; Dell’Erba, G.; Gandini, M.; D’Innocenzo, V.; Neutzner, S.; Kandada, A. R. S.; Grancini, G.; Binda, M.; Prato, M.; Ball, J. M.; et al. Ion Migration and the Role of Preconditioning Cycles in the Stabilization of the J - V Characteristics of Inverted Hybrid Perovskite Solar Cells. Adv. Energy Mater. 2016, 6, 1501453.
Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, United States *Address correspondence to: [email protected]
Breakdown mechanisms Breakdown of a p-n junction refers to the phenomenon where sufficiently high electric field due to applied voltage in reverse bias (RB) regime breaks down the junction and results in large current. The key characteristics of common breakdown mechanisms are as follows:1,2 (1) Thermal instability: In p-n junctions with large reverse saturation current, the power dissipated due to increased reverse current raises the junction temperature, consequently initiating the breakdown and destruction of the diode. The impact of breakdown due to thermal instability is irreversible. (2) Tunneling: In heavily doped p-n junctions, under large electric field in reverse bias, the carriers can tunnel through the narrow depletion region and result in Zener breakdown. This mechanism is responsible for the breakdown in a tunnel diode, with threshold voltage typically shifted to 0 V. Further, in a tunnel diode, non-linear current-voltage relationship and negative resistance (NR) region observed in the forward bias is associated with tunneling. (3) Avalanche multiplication: In p-n junctions, under high enough electric field in depletion region, electron-hole pairs are generated by impact ionization process and result in Avalanche breakdown. This mechanism of breakdown is observed at larger reverse bias (RB) compared to Zener breakdown.
Generally, Avalanche and Zener breakdown do not leave an irreversible impact on the diode, unless an excessively large reverse current increases the power dissipated and burns out the device due to raise in temperature. The “knee” of these breakdown are considerably sharper than the current rise in forward direction. With the use of series-limiting resistor, diode can be utilized under breakdown conditions as a voltage stabilizer or switch.
Figure S1. Bi-exponential fit of stabilized current measured under illumination at maximum power point obtained from I-V measurements of CH3NH3PbI3 based solar cells with PEDOT:PSS and Cu:NiOx HTLs.
Figure S2. I-V scans for PEDOT:PSS based devices measured with longer delay time (1000 ms), corresponding to a scan rate of 0.01 V/s.
Figure S3. Standalone FBRB (reverse) I-V scans starting at +1.2 V (FB) and ending at different points in reverse bias (RB), indicating anomalous breakdown in CH3NH3PbI3 based solar cells with Cu:NiOx HTL.
Figure S4. Correlation between the stabilized current under illumination at (a) -0.1 V and (b) 0.2 V with corresponding values from RBFB (forward) I-V scan for CH3NH3PbI3 based solar cells with Cu:NiOx HTL.
Figure S5. Variation of the FB inflection in RBFB I-V scans (-0.2 V to 1.1 V) measured at different delay times for CH3NH3PbI3 based solar cells with Cu:NiOx HTL; 100 ms , 1000 ms and 3000 ms delay times correspond to scan rates 0.1 V/s, 0.01 V/s and 0.003 V/s respectively; inset shows the zoomed in region of FBRB scans.
Figure S6. CH3NH3PbI3 based solar cells with Cu:NiOx/PEDOT:PSS dual HTL. (a) Device structure. (b) I-V behavior for scans starting at 0 V, -0.5 V and -1 V. (c) Bi-exponential fit of stabilized current under illumination at maximum power point. (d) Statistical data of photovoltaic performance metrics.
Figure S7. Comparison of RBFB (forward) and FBRB (reverse) I-V scans under illumination for CH3NH3PbI3 based solar cells with NiOx HTL, starting at 0 V and different points in reverse bias (RB).
Figure S8. SEM and AFM morphologies of (a) & (d) ITO glass; (b) & (e) PEDOT:PSS spin coated on ITO glass; (c) & (f) NiOx spin coated on ITO glass, respectively. The calculated RMS value of roughness (RRMS) for different surfaces is specified below their corresponding AFM images. Scan parameters were kept unaltered during measurement of different surfaces; scale bars in SEM and AFM images denote 500 nm and 1 µm respectively.
Figure S9. Dependence of abnormal I-V behavior on light (1 Sun illumination) soaking at (a) short circuit, SC (Vext = 0 V) and (b) reverse bias, RB (Vext = -0.2 V) for CH3NH3PbI3 based solar cells with Cu:NiOx HTL.
Figure S10. Normalized EQE at different RB, showing consistency of spectral shape for CH3NH3PbI3 based solar cells with Cu:NiOx HTL.
Figure S11. Hypothesis for HTL dependent I-V behavior in CH3NH3PbI3 based solar cells. The electric field due to applied external reverse bias (Eext) coupled with built-in electric field (Ebi) would induce accumulation of positive and negative point defects at HTL/CH3NH3PbI3 and ETL/CH3NH3PbI3 interfaces respectively.3 Recently reported interactions4 between PEDOT:PSS and CH3NH3PbI3 could possibly relieve ion accumulation at the PEDOT:PSS/CH3NH3PbI3 interface. However, non-interacting nature of metal oxides could withhold ion accumulation5–7 near HTL and subsequently induce a compensating electric field3,8,9 (Ecomp) and accompanying doping of CH3NH3PbI3 in proximity to NiOx, ultimately responsible for the observed tunnel junction behavior; the direction of Ecomp counteracts Ebi and Eext in RB. The curved arrow at ETL/CH3NH3PbI3 interfaces highlight the possibility of I-/PCBM interaction as demonstrated recently.10
Table S1. Photovoltaic performance metrics calculated from standard I-V scans (0 V to 1.1 V, 100 ms delay time) measured after different device pre-conditioning; numbers 1-5 refer to the order of measurement.
References (1) (2) (3) (4)
(5) (6) (7)
(8)
(9)
(10)
Solymar, L.; Walsh, D. Electrical Properties of Materials, 8th ed.; Oxford University Press: Oxford, 2010. Sze, S. M.; Ng, K. K. Physics of Semiconductor Devices, 3rd ed.; John Wiley & Sons: New Jersey, 2006. Eames, C.; Frost, J. M.; Barnes, P. R. F.; O’Regan, B. C.; Walsh, A.; Islam, M. S. Ionic Transport in Hybrid Lead Iodide Perovskite Solar Cells. Nat. Commun. 2015, 6, 7497. Xia, Y.; Sun, K.; Chang, J.; Ouyang, J. Effects of Organic Inorganic Hybrid Perovskite Materials on the Electronic Properties and Morphology of poly(3,4Ethylenedioxythiophene):poly(styrenesulfonate) and the Photovoltaic Performance of Planar Perovskite Solar Cells. J. Mater. Chem. A 2015, 3, 15897–15904. Almora, O.; Guerrero, A.; Garcia-Belmonte, G. Ionic Charging by Local Imbalance at Interfaces in Hybrid Lead Halide Perovskites. Appl. Phys. Lett. 2016, 108, 043903. Li, L.; Wang, F.; Wu, X.; Yu, H.; Zhou, S.; Zhao, N. Carrier-Activated Polarization in Organometal Halide Perovskites. J. Phys. Chem. C 2016, 120, 2536–2541. Zarazua, I.; Bisquert, J.; Garcia-Belmonte, G. Light-Induced Space-Charge Accumulation Zone as Photovoltaic Mechanism in Perovskite Solar Cells. J. Phys. Chem. Lett. 2016, 7, 525–528. Tress, W.; Marinova, N.; Moehl, T.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; Grätzel, M. Understanding the Rate-Dependent J–V Hysteresis, Slow Time Component, and Aging in CH3NH3PbI3 Perovskite Solar Cells: The Role of a Compensated Electric Field. Energy Environ. Sci. 2015, 8, 995–1004. Zhao, C.; Chen, B.; Qiao, X.; Luan, L.; Lu, K.; Hu, B. Revealing Underlying Processes Involved in Light Soaking Effects and Hysteresis Phenomena in Perovskite Solar Cells. Adv. Energy Mater. 2015, 5, 1500279. De Bastiani, M.; Dell’Erba, G.; Gandini, M.; D’Innocenzo, V.; Neutzner, S.; Kandada, A. R. S.; Grancini, G.; Binda, M.; Prato, M.; Ball, J. M.; et al. Ion Migration and the Role of Preconditioning Cycles in the Stabilization of the J - V Characteristics of Inverted Hybrid Perovskite Solar Cells. Adv. Energy Mater. 2016, 6, 1501453.
