High‐Efficiency Low‐Temperature ZnO Based Perovskite Solar Cells Based on Highly Polar, Nonwetting Self‐Assembled Molecular Layers

Abstract

electron-accepting TiO 2 scaffolds require a high-temperature annealing process (≈500 °C), which limits their use with flexible substrates. Planar heterojunctionstructured PSCs have also been widely investigated because they enable adoption of low-temperature electron accepting layers (EALs). Zinc oxide, ZnO, is a strong EAL candidate because it offers good electrical properties even when prepared at low temperatures. [12][13][14][15][16] However, ZnO is used less often than mesoporous TiO 2 because it has several drawbacks. The surface properties of the ZnO layers are not favorable for growth of uniform perovskite layers with large crystal grains. This affects device performance significantly. [2,3,[7][8][9][10]17] Thus, efforts have been undertaken to improve perovskite layer quality by enhancing ZnO surface hydrophobicity. [18][19][20][21] Another shortcoming is the reverse reaction from perovskite to PbI 2 that can occur at ZnO/perovskite interfaces during perovskite layer formation. [14,[22][23][24] Two-step sequential deposition method has been employed to fabricate perovskite active layers on ZnO-EALs. This results in more reproducible synthesis of continuous, pinholefree perovskite layers than conventional single deposition methods. [15,21,[25][26][27][28][29] The perovskite layers in these reports were formed in two steps: (i) PbI 2 layer formation and (ii) perovskite layer formation, which occurred when the PbI 2 layer was immersed into an alkyl-ammonium iodide solution and annealed (80-100 °C). The sequential deposition method partially alleviated the burden of the reverse reaction that occurs at ZnO/perovskite interfaces, while helping to achieve a PCE of ≈16%. [15,30] Thus, the development of these strategies may offer a chance to further enhance low-temperature ZnO based PSC performance.Herein, we present high-efficiency, low-temperature PSCs using a strategy that combines self-assembled monolayer (SAM) modification of ZnO-EALs with sequential preparation of perovskite active layers. SAMs of the newly synthesized, highly polar molecules were constructed on ZnO-EALs and the perovskite layers were formed via sequential deposition. The SAMs acted as ZnO wetting control layers and as electric dipole layers. [1,13,19,20,[31][32][33] Modifying our SAMs enhanced the hydrophobicity of ZnO, which improved perovskite formation quality. Simultaneously, the electric dipole effect induced via Herein, this study reports high-efficiency, low-temperature ZnO based planar perovskite solar cells (PSCs) with state-of-the-art performance. They are achieved via a strategy that combines dual-functional self-assembled monolayer (SAM) modification of ZnO electron accepting layers (EALs) with sequential deposition of perovskite active layers. The SAMs, constructed from newly synthesized molecules with high dipole moments, act both as excellent surface wetting control layers and as electric dipole layers for ZnO-EALs. The insertion of SAMs improves the quality of PbI 2 layers and final perovskite layers during sequential dep...

Incorporating a Polar Molecule to Passivate Defects for Perovskite Solar Cells

“…An ATAA molecule with carboxyl groups will self‐assemble onto the ZnO surface to form the permanent dipole at the interface with direction from the perovskite layer to the ZnO layer. According to the chemical structure of ATAA, the molecular dipole moments of ATAA (6.24 D) can be calculated by density functional theory (DFT) at the B3LYP/6‐31G(d) level using the Gaussian 03 program, which is conducive to adjusting the surface WF of the ZnO ETL. To truly investigate the effect of the formed permanent dipole on the surface WF of the ZnO layer, ultraviolet photoelectron spectra (UPS) spectra of ZnO and ZnO–ATAA were measured and are plotted in Figure b, showing that the WF is lowered by about 0.28 eV and the surface highest occupied molecular orbital (HOMO) level changes by about 0.21 eV with the incorporation of the ATAA layer, as expected.…”

Efficient Bifacial Passivation with Crosslinked Thioctic Acid for High‐Performance Methylammonium Lead Iodide Perovskite Solar Cells

“…[36,42] Therefore, TA tends to anchor on the TiO 2 surface. [43] Figure 2c shows the X ray photoelectron spectroscopy (XPS) spectra of the bare TiO 2 and Adv. It should be noted that S functional group on the surface of TiO 2 -Poly(TA) plays a positive role in the formation of high-quality perovskite film due to the Lewis acid-base reaction between S and Pb 2+ .…”

Zn0.8Cd0.2S@PCBM Hybrid as an Efficient Electron Transport Layer for Air‐Processed p‐i‐n Planar Perovskite Solar Cells: Improvement of Interfacial Electron Transfer and Device Stability

“…For devices with PCBM and ZCS@PCBM ETL, the R rec is determined to be 240.7 and 363.1 Ω, respectively. Larger R rec means less current leakage and suppressed charge recombination at the interface . Moreover, EIS measurement was carried out under various bias voltages from 0.6 to 1.0 V in the dark (Figure S7, Supporting Information).…”