Correlations between Immobilizing Ions and Suppressing Hysteresis in Perovskite Solar Cells

Abstract

Ion migration has been regarded as the major cause of photocurrent hysteresis. Here we use photoluminescence (PL) and optical images, combined with Galvanostatic measurement, to detect the ionic motion. We observe an irreversible PL and optical transmittance change after electric poling. By comparing a neat perovskite film with the sample coated by poly(methyl methacrylate) (PMMA), polyethylene glycol (PEG), and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), we found that PCBM effectively inhibits ionic motion near the surface of the perovskite.We further evidenced the donor−acceptor complex formed between PCBM and perovskite, implying the mechanism of inhibited ion migration by PCBM. We close by demonstrating that PCBM can also be introduced on the top of perovskite fim in an n−i−p TiO 2 planar structure, to achieve an average 14% steady-state output over 2.3 × 10 5 s (∼64 h). This work highlights the importance of inhibiting ionic motion in perovskite solar cells.

Interfacing Pristine C60 onto TiO2 for Viable Flexibility in Perovskite Solar Cells by a Low‐Temperature All‐Solution Process

“…In the inset of Figure 4f, the current density (≈22.37 mA cm −2 ) slightly fluctuates during the period of 1000 s. As a result, the stabilized PCE over 19% shows consistency with the calculated values from the measured J-V curves. In addition to the electron transporting layer, the fullerene interlayer can also act as a passivation layer to reduce the interfacial trap states [9,15b] and as a barrier layer to confine I − ion immobilization [21] and avoid the formation of PbI 2 originated from the reaction between iodine ions (I − ) of the perovskite and oxygen vacancies of TiO 2 . In addition to the electron transporting layer, the fullerene interlayer can also act as a passivation layer to reduce the interfacial trap states [9,15b] and as a barrier layer to confine I − ion immobilization [21] and avoid the formation of PbI 2 originated from the reaction between iodine ions (I − ) of the perovskite and oxygen vacancies of TiO 2 .…”

“…[18] Rather than PC 61 BM, moreover, a pristine C 60 fullerene modification layer possesses better resistance to the PbI 2 solution. [21] However, the low-temperature solution-processed pristine fullerene interlayer has rarely been reported for highefficiency PSCs, especially those with flexibility. [21] However, the low-temperature solution-processed pristine fullerene interlayer has rarely been reported for highefficiency PSCs, especially those with flexibility.…”

Migration of cations induces reversible performance losses over day/night cycling in perovskite solar cells

“…25,30,31,[34][35][36][37][38][39][40][41][42][43] Ion migration on timescales from 10 -1 to 10 2 s has been widely investigated to explain the hysteresis of current density-voltage (J-V) curves. 36,37,40,[44][45][46][47][48] However, the impact of X and potentially A and/or B defect formation and migration on PSC performance on timescales above 10 3 s, which are indicative of long-term stability, remains unknown. 49 Little experimental evidence exists on this subject since separating reversible ion migration from any non-reversible long-term degradation is complex in real device working conditions, i.e.…”

Impact of fullerene derivative isomeric purity on the performance of inverted planar perovskite solar cells

“…21 To mitigate the effects on grain boundaries and trap states, the concept of perovskite/fullerene (P/F) heterojunctions has attracted considerable attention. 22–25 Huang et al 26 demonstrated that the trap states on the surface and grain boundaries are the origin of photocurrent hysteresis and that fullerene layers deposited on perovskites can effectively passivate these charge trap states and eliminate the undesirable photocurrent hysteresis. 26 …”