Defects Healing in Two-Step Deposited Perovskite Solar Cells via Formamidinium Iodide Compensation

Abstract

Photovoltaics based on metal halide perovskites have recently achieved a certificated efficiency of 25.2%. One of the factors that limit further development of these devices comes from the defective boundaries between crystalline domains in perovskite solar cells (PSCs). Such boundaries represent a significant loss channel causing nonradiative recombination, but systematic optimization procedures have not been developed yet to control their properties. Herein, we propose a facile but effective defect healing method to passivate the defects along the grain boundaries in PSCs by post-treatment of formamidinium iodide (FAI) solution in isopropyl alcohol (IPA). We use a combination of methods including space-charge-limited current, steady-state and time-resolved photoluminescence, confocal laser scanning microscopy, and transient absorption spectroscopy to show the reduction of density of defect states in perovskite films processed with 1 mg/mL FAI solution. The resultant FAI healed PSCs achieve an average power conversion efficiency of 19.26% (with a champion efficiency of 20.62%), higher than that of 16.45% in the control cell. FAI healed devices without encapsulation maintain nearly 95% of the initial efficiency after 60-day storage under N 2 environment and nearly 78% of the initial efficiency after 30-day storage under the ambient condition with varied humidity. Our results demonstrate that FAI healing is an effective way to passivate the defect states along grain boundaries for high-efficiency and stable PSCs.

Stability of Perovskite Solar Cells: Degradation Mechanisms and Remedies

“…The strategy of alloying is also important. We adopted a method of posttreatment where FAI solution in isopropanol is used to treat the perovskite film (Xin et al, 2020). It is proven to be highly effective in passivating the defects.…”

“…S-moiety in WS 2 has also proven to be effective (Xu et al, 2020). Poly (thioctic acid) is highly hydrophobic and presence of both C S and C O can effectively passivate the defects and yield a stable device (Xin et al, 2020).…”

Toward Efficient and Stable Perovskite Solar Cells: Choosing Appropriate Passivator to Specific Defects

“…Most recently, defect passivation as a practical approach to suppress the charge recombination dynamics and heighten the performance of PSCs has been widely demonstrated, as shown by the remarkably increasing number of publications in Figure a. [ 36–38 ] Shao et al first introduced the concept of passivation by depositing the fullerene on the surface of perovskite absorbers to eliminate hysteresis for inverted planar PSCs. [ 39 ] Since then, increasing numbers of new passivation molecules, for instance, salts, [ 40,41 ] polymers, [ 42–44 ] and organic or inorganic molecules, [ 45,46 ] have been applied to reduce the defects by the strong interaction between perovskite and passivation molecules, as shown in Figure 1b, suppressing the influence of the external stresses, and advancing the photovoltaic performance of PSCs.…”

Water Stable Haloplumbate Modulation for Efficient and Stable Hybrid Perovskite Photovoltaics

“…This is likely caused by the passivation of defects on the surface and at the grain boundaries of the perovskite. [58] To quantify the electron-trap densities (n t ) in the control and [TBA]PbI 3 -modulated devices, the space-charge-limited-current (SCLC) measurements were performed (experimental details are provided in the Experimental Section) with an electron-only device structure of ITO/SnO 2 /FA 1-x MA x PbI 3 /PCBM/Au (ITO for indium tin oxide; Figure S11, Supporting Information). [53,59] The trap filled limit voltage (V TFL ) decreases from 1.050 to 0.625 V, corresponding to the reduced density of trap states in the perovskite film from 9.9 × 10 15 to 5.9 × 10 15 cm −3 upon TBAI treatment, which is particularly relevant for the photovoltaic performances.…”