Role of Methylammonium Orientation in Ion Diffusion and Current–Voltage Hysteresis in the CH₃NH₃PbI₃ Perovskite

Abstract

Hybrid organic−inorganic perovskites, and particularly CH 3 NH 3 PbI 3 (MAPbI 3 ), have emerged as a new generation of photovoltaic devices due to low cost and superior performance. The performance is strongly influenced by current−voltage hysteresis that arises due to ion migration, and the challenge remains how to suppress the ion migration and hysteresis. Our first-principles calculations demonstrate that the energy barriers to diffusion of the I − , MA + , and Pb 2+ ions are greatly affected by dipole moments of the MA species. The energy barriers of the most mobile I − ion range from 0.06 to 0.65 eV, depending on MA orientation. The positively charged MA + and Pb 2+ ions diffuse along the dipole direction, while the negatively charged I − ion strongly prefers to diffuse against the dipole direction. By influencing ion migration, the arrangement of MA molecules can effectively modulate the current−voltage hysteresis intensity. The current work contributes to the fundamental understanding of the microscopic mechanism of ion migration in MAPbI 3 and suggests means to suppress the hysteresis effect and optimize perovskite performance. By demonstrating in detail how the arrangement of the organic molecules can efficiently influence ion migration and, hence, amplitude of the current−voltage hysteresis, our results suggest that the hysteresis effect can be suppressed and the long-term performance of perovskites can be improved, if the organic molecules are arranged and stabilized in an antiferroelectric order.

Extending Carrier Lifetimes in Lead Halide Perovskites with Alkali Metals by Passivating and Eliminating Halide Interstitial Defects

“…Interstitial iodine defects introduce trap states inside the fundamental band gap and accelerate nonradiative electron–hole recombination. Furthermore, iodine interstitials readily migrate with the low activation energy of 0.29 eV, leading to device degradation and the undesirable current–voltage hysteresis . Studies demonstrating the detrimental role of iodine interstitials raise the question of how to eliminate or passivate these defects.…”

“…Furthermore,iodine interstitials readily migrate with the low activation energy of 0.29 eV, [15] leading to device degradation and the undesirable current-voltage hysteresis. [15,16] Studies demonstrating the detrimental role of iodine interstitials raise the question of how to eliminate or passivate these defects. Theory indicates that adjusting the oxidation state of the interstitial iodine can control carrier dynamics and reduce nonradiative carrier recombination.…”

Divalent Anionic Doping in Perovskite Solar Cells for Enhanced Chemical Stability

“…Organic–inorganic hybrid metal halide perovskites (ABX 3 , A = CH 3 NH 3 + , (NH 2 ) 2 CH + , B = Pb 2+ , Sn 2+ , and X = Cl − , Br − , I − ) emerges as the most focused photovoltaic (PV) material, in which methylammonium lead iodide, (CH 3 NH 3 PbI 3 or MAPbI 3 ) represents the best performer in terms of efficiency, light absorber (1.5 × 10 4 cm −1 at 550 nm), charge generation, carrier diffusion lengths, and lifetimes . Despite such prominences, it is still battling against several inherent problems, including lead toxicity, low chemical/device stabilities in moisture, current–voltage hysteresis, and migration of iodine that plagues device electrodes …”

“…AgI consequently creates large resistivity at the charge collection electrode and accounts for the drop of PV performance on regular MAPbI 3 cell. Atomically, Se 2− poses strong electrostatic interaction with MA + in perovskite materials, suppressing librational motions of MA + , reducing iodine migration . As such, PbSe dopant effectively aid in suppressing iodine diffusion and contributes to stable solar cell performance.…”

Indirect but Efficient: Laser-Excited Electrons Can Drive Ultrafast Polarization Switching in Ferroelectric Materials

“…For example, tuning the FE polarization can vary the tunneling resistance over several orders of magnitude [1], enabling technological advancements such as non-volatile memory in digital electronic devices, [2] memristors, [3] and integrated neuromorphic networks [4,5]. In addition, by enabling a steady-state photocurrent, the use of FE polarization can substantially increase light-harvesting efficiency, particularly in hybrid organic-inorganic halide perovskite solar cells [6][7][8][9][10][11][12][13][14][15][16][17]. Finally, the variation in FE polarization on surfaces can also dramatically change the adsorption energetics in catalytic systems and could be further harnessed to enable other polarization-dependent surface mechanisms [18,19].All of these applications are intrinsically associated with FE polarization and can, therefore, be further enhanced by tuning and controlling this intrinsic material property.…”