Fluorinated Interfaces for Efficient and Stable Low‐Temperature Carbon‐Based CsPbI₂Br Perovskite Solar Cells

Abstract

Carbon-based inorganic perovskite solar cells (C-PSCs) have attracted intensive attention owing to their low cost and superior thermal stability. However, the bulk defects in perovskites and interfacial energy level mismatch seriously undermine their performance. To overcome these issues, a multifunctional dualinterface engineering is proposed with a focus on low-temperature CsPbI 2 Br C-PSCs, where the potassium trifluoroacetate (KTFA) and the 4-trifluorophenyl methylammonium bromide (CF 3 PMABr) are introduced beneath and on top of the perovskite layer, respectively. It is found that TFAions locate at the SnO 2 /CsPbI 2 Br interface, whereas a small amount of K + ions diffuse into perovskite lattice to participate in nucleation and crystallization, resulting in more favored interfacial energy level alignment, improved film quality, passivated interfacial defects, released interfacial strain, as well as suppressed charge recombination and ion migration. Meanwhile, the CF 3 PMABr passivates I/Br vacancies and forms 2D perovskite capping layer to facilitate hole extraction at the CsPbI 2 Br/carbon interface. As a result, a remarkable power conversion efficiency (PCE) of 14.05% with an open-circuit voltage of 1.273 V is achieved. To the best of the authors' knowledge, it is currently the highest PCE reported for low-temperature CsPbI 2 Br C-PSCs. Furthermore, the nonencapsulated device exhibits improved moisture, thermal, and illumination stability in ambient air.

The synergistic effect of defect passivation and energy level adjustment for low-temperature carbon-based CsPbI2Br perovskite solar cells

“…21,42,43 The hydrophobic fluorinated materials can prevent the intrusion of H 2 O molecules into perovskite films. 7,39 Therefore, the above four organic ammonium halide salts are expected to further improve the performance of CsPbI 2 Br C-IPSCs.…”

“…6 In addition, the low glass transition temperature (125 °C) of 2,2′,7,7′-tetrakis[ N , N -di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (Spiro-OMeTAD) can degrade device performance under thermal stress. 7 The metal electrodes are susceptible to ion migration from perovskites, and the hygroscopic and deliquescent additives in organic hole transport layers (HTLs) can also accelerate device degradation. 8,9 Because Spiro-OMeTAD requires oxygen, it is difficult to control its oxidation process.…”

Low Temperature Processed SnO2 Electron Transporting Layer from Tin Oxalate for Perovskite Solar Cells

“…13,20 In Figure 1a, two distinct XPS peaks located at 495.7 and 487.3 eV can be observed, which are assigned to Sn 3d 3/2 and Sn 3d 5/2 states of Sn 4+ in SnO 2 . 13,21,22 Although the H 2 O 2 volume used to dissolve the tin oxalate are different, the binding energies of the XPS peaks are coincident with each other, which might be due to the complete oxidation of Sn 2+ to Sn 4+ by H 2 O 2 . In fact, the minimum H 2 O 2 needed to fully oxidizing tin oxalate is estimated to be ∼150 μL.…”

Progress and Perspective on Inorganic CsPbI2Br Perovskite Solar Cells

“…PSCs with ATI maintained 85% of initial PCE for 200 h at 80 °C and in humid air environment (Figure 12c), much better than the control sample. Tai et al [49] modified the 4-trifluorophenyl methylammonium bromide (CF 3 PMABr) and potassium trifluoroacetate (KTFA) at the upper and lower interfaces of CsPbI 2 Br perovskite, respectively. TFA − was located at the SnO 2 /CsPbI 2 Br interface, K + diffused into the perovskite bulk phase, and CF 3 PMABr formed 2D perovskite on the surface of CsPbI 2 Br.…”

“…Benefitting from these advantages, the first reported CsPbI 2 Br PSCs achieved a PCE of 9.8%, [41] and the PCE has increased to 17.5% after just several years. [45,46] However, inorganic CsPbI 2 Br still has several problems that restricted device performance, such as higher sintering temperature, [40,47] defects of the perovskite, [48,49] considerable energy loss (E loss ), [32,40] energy level mismatch with carrier transport layers, [50,51] etc. Many studies have proposed a series of strategies to resolve the above issues, including optimization of the preparation process, [52,53] additive technique, [54,55] interface modification, [38,56] dimensional regulation, [57,58] and optimization of the novel carrier transport layers.…”