Stable 24.29%‐Efficiency FA_0.85MA_0.15PbI₃ Perovskite Solar Cells Enabled by Methyl Haloacetate‐Lead Dimer Complex

Abstract

The remarkable high PCE of hybrid PSCs relies on the unique advantages of perovskite materials (high light-absorption coefficient, [7] broad lightabsorption range, [8] fast charge-carrier mobility, [9] long diffusion length, [10] tunable bandgap, [11] small exciton binding energy, [12] etc.) and effective structural and surface modifications (compositional engineering, interfacial passivation, additive engineering, etc.). [13][14][15][16] Perovskites based on FA x MA 1−x PbI 3 (FA, formamidinium; MA, methylammonium) have been widely applied in hybrid PSCs due to their lower bandgap and higher solar light-harvesting efficiency in contrast to MAPbI 3 . [17][18][19][20][21] Compared with FAPbI 3 , partial substitution of FA (ionic radius = 2.79 Å) with MA (ionic radius = 2.17 Å) could improve the stability of hybrid PSCs due to the reduced tolerance factor to the appropriate range (0.8-1). [22,23] However, the low-boilingpoint MA cations easily escape from the perovskite lattice during the device fabrication process, and the large FA cations are impeded from embedding into the MA vacancies due to their weak interaction with the established lattice, both of which lead to many defects (MA/FA vacancies, undercoordinated Pb 2+ , and Pb I antisites) at the surface and interface of the perovskite. [24][25][26] Those defects always act as non-radiative recombination Formamidinium methylammonium lead iodide (FAMAPbI 3 ) perovskite has been intensively investigated as a potential photovoltaic material because it has higher phase stability than its pure FAPbI 3 perovskite counterpart. However, its power conversion efficiency (PCE) is significantly inferior due to its high density of surface detects and mismatched energy level with electrodes. Herein, a bifunctional passivator, methyl haloacetate (methyl chloroacetate, (MClA), methyl bromoacetate (MBrA)), is designed to reduce defect density, to tune the energy levels and to improve interfacial charge extraction in the FAMAPbI 3 perovskite cell by synergistic passivation of both CO groups and halogen anions. As predicted by modeling undercoordinated Pb 2+ , the MBrA shows a very strong interaction with Pb 2+ by forming a dimer complex ([C 6 H 10 Br 2 O 4 Pb] 2+ ), which effectively reduces the defect density of the perovskite and suppresses non-radiative recombination. Meanwhile, the Br − in MBrA passivates iodine-deficient defects. Consequently, the MBrA-modified device presents an excellent PCE of 24.29%, an open-circuit voltage (V oc ) of 1.18 V (V oc loss ≈ 0.38 V), which is one of the highest PCEs among all FAMAPbI 3 -based perovskite solar cells reported to date. Furthermore, the MBrA-modified devices without any encapsulation exhibit remarkable long-term stability with only 9% of PCE loss after exposure to ambient air for 1440 h.

Revealing superoxide-induced degradation in lead-free tin perovskite solar cells

“…4(a), where the halide anion aims to fill V I . 33,34 Hereafter, FASnI 3 in the devices is doped with the commonly used ethylenediammonium diiodide (EDAI 2 ) to achieve high-quality films. 35,36 The reason why the additives containing I-site were not chosen here is that we found that the EDAI 2 additive has weak suppression of the superoxide formation for FASnI 3 (Fig.…”

24.20%‐Efficiency MA‐Free Perovskite Solar Cells Enabled by Siloxane Derivative Interface Engineering

“…As shown in Figure 1h, the electron mobility of control TiO 2 and PSiOH-modified TiO 2 films is evaluated by employing the space charge limited current (SCLC) method under dark conditions. [28] The electron mobility of PSiOHmodified TiO 2 film (1.15 × 10 -3 cm 2 V -1 S -1 ) is 1.45 times higher than that of control TiO 2 film (0.79 × 10 -3 cm 2 V -1 S -1 ), which is conducive to effective collection of photogenerated charge. The electrical conductivity (σ) is obtained from the slope of I-V curve combined with an equation of I = σAL -1 V, where A is active area, L is film thickness.…”

A residual strain regulation strategy based on quantum dots for efficient perovskite solar cells

“…All the perovskite lms have diffraction peaks at 14.1°and 28.2°corresponding to the (001) and (002) planes of FAPbI 3 , which is consistent with previous research results. [29][30][31][32] This also indicates that the introduction of the CsPbI 3 QDs does not change the phase and crystal structure of the perovskite lms. The intensities of the (001) and (002) orientation peaks of the QD treated lm are higher than those of the control lm.…”