Hole-Transport-Underlayer-Induced Crystallization Management of Two-Dimensional Perovskites for High-Performance Inverted Solar Cells

Abstract

Currently, intensive research is being conducted on Ruddlesden–Popper-type two-dimensional (2D) perovskite-based solar cells because of the advantages such as excellent power conversion efficiency (PCE) and desirable environmental stability. A well-crystallized perovskite film plays a very important role in enhancing the performance of perovskite solar cells (PSCs). In this study, we investigated the effect of the wetting property of the underlying hole-transport layer (HTL) on the crystallization of 2D perovskite films. Three HTL layers with varied hydrophobicities, including hydrophilic poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS), moderate-hydrophobic poly­(bis­(4-phenyl)­(2,4,6-trimethylphenyl)­amine) (PTAA), and high-hydrophobic poly­(3-hexylthiophene-2,5-diyl) (P3HT), were used to fabricate 2D PSCs, and the quality of the resulting perovskite films was examined. We found that moderate-hydrophobic PTAA resulted in a compact and uniform perovskite morphology with enhanced crystallinity. By contrast, the perovskite film formed on hydrophilic PEDOT:PSS showed a rough morphology with overlapping perovskite planes. This is because the hydrophobic PTAA surface could suppress the heterogeneous nucleation of perovskite and facilitate the boundary mobility of perovskite grains. Therefore, a high PCE value of 12.3% was achieved for the PTAA-based PSCs, which is higher than that of the PSCs using PEDOT:PSS (10.5%). However, the perovskite film formed on the highly hydrophobic P3HT showed a low surface coverage, resulting in an even lower PCE of 8.3%. This might be due to the higher hydrophobicity of P3HT, which leads to a low adhesion force with the precursor. The 2D PSCs using PTAA also show better long-term and thermal stability than the PEDOT:PSS-based case, with a suppressed PCE degradation from 26 to 17%. Our results indicate that using moderate-hydrophobic PTAA as the HTL is beneficial for fabricating efficient 2D PSCs with higher stability.

Green-Solvent-Processable Low-Cost Fluorinated Hole Contacts with Optimized Buried Interface for Highly Efficient Perovskite Solar Cells

“…The surface hydrophobicity and hydrophilicity of the hole contact have significant impacts on the perovskite film formation and perovskite crystal growth . On the premise of good wetting for perovskite precursor solution, high hydrophobicity of the hole contact is more likely beneficial to achieving large perovskite grains with less grain boundaries, and more perovskite nuclei with small perovskite grain sizes and a large amount of grain boundaries easily form on the substrate surface with high hydrophilicity. , On the other hand, it was found that the highly hydrophobic surface with a water contact angle >100° fails to facilitate the perovskite wetting and deposition . Hence, it is important to optimize the surface hydrophobicity and hydrophilicity.…”

High-performance wide-bandgap perovskite solar cells with an enhanced photon-to-electron response of near-infrared wavelengths

“…22 The cross-point of the ohmic and TFL regimes is known as the trap-filled limit voltage (V TFL ), which is determined by the trap states. 37 Hence, the trap density (n trap ) of the devices can be calculated from the following eqn (1):…”

A Universal Strategy of Perovskite Ink ‐ Substrate Interaction to Overcome the Poor Wettability of a Self‐Assembled Monolayer for Reproducible Perovskite Solar Cells

“…[19][20][21] The mismatch between the polarity leads to high contact angles and severe wetting issues of perovskite solution on the hydrophobic HTLs and thus results in poor surface coverage, pinholes, high charge carrier recombination, low open-circuit voltage (V OC ), and device performance. [10,[22][23][24] In addition to hydrophobic polymeric HTLs, recently, carbazole-based self-assembled monolayers (SAMs) with phosphonic acid anchoring groups such as [2-(9H-Carbazol-9-yl)ethyl]phosphonic acid (2PACz), [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz), and [4-(3,6-Dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) have been in the limelight because of their better energy level alignment with some of the most relevant perovskite compositions with high device efficiencies. [25][26][27][28][29][30] In particular, Me-4PACz-based perovskite solar cells showed one of the highest efficiency for p-i-n-type devices both in single junction and tandem (with silicon) configurations.…”