Elucidating Mechanisms behind Ambient Storage-Induced Efficiency Improvements in Perovskite Solar Cells

Abstract

Initial improvement in power conversion efficiency (PCE) during ambient storage is often seen in perovskite solar cells (PSCs). In this work, we studied the origin of PCE enhancement by ambient storage on typical n-i-p PSCs. We found improvements in both fill factor and opencircuit voltage during the first two days of storage. By analyzing temperature and light intensity dependent VOC, we found that the charge recombination mechanism changed from surface-to A Self-archived copy in Kyoto University Research Information Repository https://repository.kulib.kyoto-u.ac.jp bulk-dominated due to defect passivation at the perovskite surface upon storage. In addition, we found that storage improves the conductivity and lowers the highest occupied molecular orbital level of the spiro-OMeTAD improving charge extraction. These results show that there are more than one factor causing the storage-induced-improvements in perovskite solar cells.

The effect of storage cycle on improvement in the photovoltaic parameters of planar triple cation perovskite solar cells

“…Higher ideality factor value, for stored devices completed outside the GB, indicates the dominant existence of trap−assisted recombination, but considering the increase of V oc , compared to pristine devices, a reduction of traps or non-radiative recombination could be occurred. 46 Conversely, smaller n id , calculated for stored devices completed inside the GB, is attributed to a band-to-band direct recombination also confirmed from higher values of V oc respect to all the other devices. This is reliable with results.…”

“…Oxygen and moderate moisture have then a positive effect on the photovoltaic performances, but prolonged exposure in humid air can lead to acute degradation of PSCs. 8,46,53,54 The former mechanism which leads to increase the conductivity could be assigned to effect of water molecules n-type dopant 42,43 and the filling of deep charge carrier traps. 41,43,44 The latter mechanism could be the oxidation of Spiro-OMeTAD that increases the charge transfer at the perovskite/Spiro-OMeTAD/gold interfaces, decreasing series resistance, R s .…”

“…Some papers reported the value of ideality factor for aged and pristine devices, suggesting that the unity value of n indicates the dominance of recombination at the surface of the perovskite film, whereas n id < 2 refers to trap-assisted Shockely-Read-Hall (SRH) recombination in the perovskite bulk. 46,67 Authors found that for aged devices was dominant SRH recombination. For our devices the ideality factor was calculated from the slope of V oc vs ln( ph /) reported in Fig.…”

“…Whilst moderate levels of humidity would positively affect to have high efficiency, at high levels of moisture or prolonged time exposure at low humidity, the PCE would decrease because of formation of hydrate phase perovskite. 5,[7][8][9][10][11]45,46 About that, just recently, Cho et al 46 clarified the mechanism that induces PCE increasing after ambient and moderate humidity storage in n-i-p architecture based on mesoporous perovskite solar cells, with 200 nm mesoporous TiO 2 as ETM and 400 nm capping perovskite layer. They found a PCE increasing in double cation perovskite, in the first 48 h of storage, from 17.1 % to 20.4 %, at room temperature and moderate humidity, finding that the effect of moisture on initial cell performance improvement was a combined result of temporal changes in both perovskite and HTM, showing a surface passivation and changes in conductivity.…”

Enhanced Efficiency of Inorganic CsPbI3−xBrx Perovskite Solar Cell via Self‐Regulation of Antisite Defects

“…They attributed the improved performance to both reduced trap-mediated recombination centers in perovskite layer, especially from the perovskite surfaces and improved conductivity and better level alignment of hole transport layer. [43] We next explored the possible driving force for the self-regulation behavior. The thermodynamic possibility was assessed by the Gibbs free energy calculated in terms of the defect reaction equation for five structural models in Figure 3.…”