Persistent Ion Accumulation at Interfaces Improves the Performance of Perovskite Solar Cells

Abstract

The mixed ionic–electronic nature of lead halide perovskites makes their performance in solar cells complex in nature. Ion migration is often associated with negative impacts—such as hysteresis or device degradation—leading to significant efforts to suppress ionic movement in perovskite solar cells. In this work, we demonstrate that ion trapping at the perovskite/electron transport layer interface induces band bending, thus increasing the built-in potential and open-circuit voltage of the device. Quantum chemical calculations reveal that iodine interstitials are stabilized at that interface, effectively trapping them at a remarkably high density of ∼10 21 cm –3 which causes the band bending. Despite the presence of this high density of ionic defects, the electronic structure calculations show no sub-band-gap states (electronic traps) are formed due to a pronounced perovskite lattice reorganization. Our work demonstrates that ionic traps can have a positive impact on device performance of perovskite solar cells.

Perovskite ionics – elucidating degradation mechanisms in perovskite solar cells via device modelling and iodine chemistry

“…This is further supported by the characterisation of the bulk of the perovskite layer by ultra-violet photoemission spectroscopy depth profiling, which reveals the bulk of three-dimensional perovskites to be strongly n-type. 41…”

“…This is further supported by the characterisation of the bulk of the perovskite layer by ultra-violet photoemission spectroscopy depth profiling, which reveals the bulk of three-dimensional perovskites to be strongly n-type. 41 In our study, we use a semiconductor device model framework to examine the effect of the mobile iodide anions and their chemistry on the electrical properties of the solar cell. This was studied in part by Bertoluzzi et al, 36 but we expanded the physical picture and focused on the bias range where the solar cell operates rather than on reverse bias effects.…”

Polymer‐Assisted Heterogeneous Lead Iodide in a Two‐Step Process: Fabrication of Efficient and Stable Perovskite Solar Cells

“…Depending on the calculation of hysteresis index (HI) = (PCE RS −PCE FS )/PCE RS , the HI for the control device is 0.089, while the HI for the PVA‐incorporated device is reduced to 0.046. [ 54 ] The PVA‐modified device presents smaller hysteresis behavior, which originates from the passivated grain boundaries and decreased defect states in the PVA‐introduced perovskite films. In addition, the integrated J SC from the external quantum efficiency (EQE) spectra are 23.35 mA cm −2 for the control device and 24.27 mA cm −2 for the PVA‐incorporated device, respectively (Figure 5c).…”

“…For the KPFM images in Figure 3a,b, one can observe that the PVA‐modified perovskite film exhibits higher surface potential (−88.90 mV) than the control film (−222.22 mV), indicating the interaction between PVA and perovskite on the surface of the PVA‐modified perovskite film. [ 52–54 ] Moreover, compared to the control sample, the surface potential distribution of the PVA‐modified perovskite film is relatively more uniform (Figure 3c), implying reduced surface defects/energy barrier among grains and thus inhibited nonradiation recombination of carriers in the PVA‐induced perovskite film. [ 52 ]…”

Uncovering the Influence of Cation Composition Engineering on the Ion Migration Kinetics in Perovskite Solar Cells

“…The impact of ion migration on the charge transfer kinetics ( i.e. , the slow V ph buildup) can be explained by the ion accumulation-induced inverse band bending at the electrode/perovskite interface, which is further embodied by the accelerated charge recombination, a higher open-circuit voltage, and/or the enhanced built-in potential . What has been also well established is that the halide anions should migrate faster than the organic cations because of the lower migration activation energy; on the other hand, as limited by the extremely high migration path barrier, Pb 2+ is almost immobile …”