A One‐Step Ionic Liquid Interface‐to‐Bulk Modification for Stable Carbon‐Based CsPbI₃ Perovskite Solar Cells with Efficiency Over 15%

Abstract

as methylammonium and formamidinium), resulting in the relatively poor long-term stability of PSCs. For another, Au electrodes and organic hole transport layers such as 2,2′,7,7′-Tetrakis(N,N-di-pmethoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) commonly used in organic-inorganic hybrid PSCs are expensive, which weakens the cost advantage of devices. Aiming at these problems, hole transport layer-free, all-inorganic carbonbased PSCs (C-PSCs) with a device structure of fluorine-doped tin oxide (FTO) or tin-doped indium oxide (ITO)/electron transport layer (ETL)/inorganic perovskite/carbon, would be a potential alternative to achieve low cost, high-efficiency, and high stability, simultaneously. [3][4][5][6][7][8][9][10] Among many inorganic perovskites, CsPbI 3 perovskite has the greatest application potential due to its ideal band gap (≈1.70 eV). [11][12][13][14][15][16][17] To pursue highly efficient and stable CsPbI 3 C-PSCs, developing stable and high-quality CsPbI 3 perovskite film with fewer defects is a prerequisite. Xiang et al. discovered air-stable CsPbI 3 film can be obtained by one-step solution deposition method using HPbI 3 instead of PbI 2 , and a PCE of 9.5% was achieved for CsPbI 3 C-PSCs by employing such perovskite film. [18] Then, by doping Natrium in the CsPbI 3 lattice, they further boosted the PCE of CsPbI 3 C-PSCs to 10.7%. [19] Liang et al. boosted the PCE of CsPbI 3 C-PSCs to 12.04% by developing CsPbI 3 :Br:InI 3 , which possesses the same bandgap as CsPbI 3 but has significantly reduced defect density. [20] Wang et al. systematically studied the crystallization of CsPbI 3 films after dimethylammonium iodide (DMAI) treatment, which boosts the efficiency of CsPbI 3 C-PSCs to 14.6%. [21] Recently, Wang et al. adopted the CsPbI 3 film post-processing strategy to form the energy level gradient and generate a 2D Cs 2 PbI 2 Cl 2 nanosheets structure as the electronic blocking layer, which boosts the efficiency of CsPbI 3 C-PSCs to 15.23%. [22] Even though many efforts have been made to achieve high-quality CsPbI 3 films as well as efficient CsPbI 3 C-PSCs, the relatively poor crystallinity is accompanied by many defects of CsPbI 3 film is still the main obstacle for further boosting the PCE of CsPbI 3 C-PSCs.Hole transport layer-free, carbon-based, all-inorganic CsPbI 3 perovskite solar cells (PSCs) have exhibited great potential in photovoltaic applications owing to their low cost and excellent thermal stability. However, the low power conversion efficiency (PCE) hampers its development, mainly due to the existence of defects inside the CsPbI 3 film or at TiO 2 electron transport layer/CsPbI 3 interface. Herein, these issues were addressed through a facile TiO 2 post-treatment strategy using 1-butyl-3-methylimidazole hexafluorophosphate (BMIMPF 6 ) ionic liquid. First, BMIMPF 6 can passivate TiO 2 /CsPbI 3 interface defects by forming strong bond between the electron-rich N atoms and uncoordinated ions. Second, BMIMPF 6 -modified TiO 2 shows reduced hydrophilicity, inducing decreased he...

Surface Passivation of CsPbI 3 Films for Efficient and Stable Hole-Transporting Layer-Free Carbon-Based Perovskite Solar Cells

“…Furthermore, Mott−Schottky plots of both devices were measured in dark conditions. 27 As shown in Figure 6c, the build-in potential (V bi ) increased from 0.94 to 1.01 V after OAI treatment, indicating that the OAI-treated device has an enhanced driving force for carrier separation, and this is consistent with its increased V oc . 48 Figure 6d shows the dependence of V oc on various light intensities with and without OAI treatment, compared with the control CsPbI 3 C-PSC, which shows a slope of 2.12 K B T/q.…”

“…Generally, reduced R s as well as increased R sh is beneficial to improve device performance. Furthermore, Mott–Schottky plots of both devices were measured in dark conditions . As shown in Figure c, the build-in potential ( V bi ) increased from 0.94 to 1.01 V after OAI treatment, indicating that the OAI-treated device has an enhanced driving force for carrier separation, and this is consistent with its increased V oc …”

“…24−26 Thus, HTL-free inorganic CsPbI 3 carbon-based PSCs (C-PSCs) with greatly reduced cost as well as improved long-term operation stability show promising commercial prospects. 27,28 Since the first report of HTL-free inorganic CsPbI 3 C-PSCs with a low PCE of 4.65% by Liang et al, 29 many efforts have been made to improve the efficiency of this kind of device, including composition manipulation, 30−32 element doping, 33 interface engineering, 34,35 process optimization, 13,14 etc., which significantly boost the PCE of CsPbI 3 C-PSCs to over 16% till now. 36,37 Especially, Chen's group pioneered the highefficiency CsPbI 3 C-PSCs via composition manipulation, which demonstrated that carefully controlling the precursor ratios of dimethylammonium iodide (DMAI)/PbI 2 /CsI can suppress the formation of δ-CsPbI boosting the PCE of CsPbI 3 C-PSC to 14.6%.…”

“…Apart from efficiency and stability, the cost of PSCs should also be carefully considered. − Generally, high-efficiency PSCs use a structure of ITO or FTO/electron-transporting layer (ETL)/perovskite/hole-transporting layer (HTL)/Au. Among them, the commonly used organic HTLs (e.g., Spiro-OMeTAD) as well as Au electrodes are expensive and may bring about instability issues, which suggests that these may not be the ultimate choice of the market. − Fortunately, researchers found that low-cost carbon electrodes can simultaneously replace organic HTLs and Au electrodes, endowing PSCs with a decent PCE. − Thus, HTL-free inorganic CsPbI 3 carbon-based PSCs (C-PSCs) with greatly reduced cost as well as improved long-term operation stability show promising commercial prospects. , …”

Forming a composite electron blocking layer to enhance the performance of carbon-based CsPbI3 perovskite solar cells

“…20–25 Among various inorganic perovskites, CsPbI 3 has shown great prospects duo to the suitable bandgap of 1.73 eV. 26–32 So far, great progress has been made on CsPbI 3 C-PSCs and over 16% PCE has been achieved. 33…”