Covalent organic nanosheets for effective charge transport layers in planar-type perovskite solar cells

Abstract

Herein, solvent-treated bandgap-tunable covalent organic nanosheets (CONs) were prepared via the Stille cross-coupling reaction. These materials are considered useful as interlayers in photovoltaic devices upon the alignment of energy levels between other components. Among various types of solar cells, according to the organic-interlayer study, inverted planar perovskite solar cells (PSCs) are mostly demanded to effectively transport and collect charge carriers due to their high performance. At first, the C-V analysis proved the energy levels of the frontier orbitals for CON-10 and CON-16 nanosheets; this verified the suitability of these nanosheets as hole transport layers (HTLs) with the PEDOT:PSS upon casting both films from DMSO. It became evident, however, that the hole transport property of the PEDOT:PSS on the CON-16 layer was unfavorable with the increasing UPS-proven hole injection barrier. In addition, both CONs induced a rough surface morphology; however, CON-10 showed a relatively smooth surface as compared to CON-16 based on the Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) profiles; furthermore, their surface properties influenced both the PEDOT:PSS layers and the perovskite layers. Especially, the XRD profiles presented an enhanced crystallinity of the perovskite layers with CON-10. All these aspects indicate that CON-10 is a more effective HTL material, and several versions of perovskite solar cells (PSCs) have been fabricated with/without CON-10 and CON-16 together with the PEDOT:PSS to determine the more-HTL-suitable CON. As a result, the power conversion efficiencies (PCEs) of the optimized devices with CON-10 exhibited a value of 10.2%, which represented a 1% increase over those of the reference devices without the CONs and was 4% higher than that of the CON-16 devices. Moreover, the devices with CON-10 were further optimized with TiO using Al electrodes, leading to a PCE increase of these devices that became slightly higher than the PCEs of the device with CON-10 and without TiO. This tendency was supported by photoluminescence (PL) spectroscopy, photocurrent density (J), and space-charge-limited current (SCLC) mobility results.

Covalent–Organic Frameworks: Advanced Organic Electrode Materials for Rechargeable Batteries

“…[ 91 ] In order to remedy the above‐mentioned defects, Stille cross‐coupling reaction was adopted by Park et al to prepare CONs with a weak aggregation tendency, as well as an enhanced colloidal stability in organic solvents. [ 92,93 ] The as‐prepared CONs were characterized to display 2D lamellar morphology, which can be regarded as the delaminated COFs. Park and co‐workers found that through a precise control of reaction conditions and monomer combination, the as‐obtained CONs were adjustable on specific surface area, self‐assembled morphology, and molecular planarity.…”

2D framework materials for energy applications

“…Park and co-workers illustrated in a study the use of a 2D COF prepared by the Stille coupling as a hole transport layer in perovskite solar cells. 207 In device arrangements featuring the 2D COF, an increase in power conversion efficiency of 1% is observed. Generally speaking, the use of 2DFMs in photovoltaics are still only scarcely researched, even though plenty of studies on 3D and layered framework materials exist, still there is a long way to go to reach the full potential of these materials.…”

Versatile Pendant Polymer for Selective Charge Carrier Transport via Controlling the Supramolecular Self‐Assembly

“…In the line with this research trend, we previously had dedicated our research endeavors to develop new types of effective interlayer materials such as triazine-based two dimensional (2D) covalent organic nanosheets (CONs) for HTLs and highly branched triazine-based porous organic polymers (T-POPs) with alkyl chains for ETLs. [5,6] Each layer showed enhanced charge carrier transport properties, mostly relying on π-π* electronic transitions. Since the surface of ETLs should be smooth for better contact with top electrodes, hyper-branched T-POPs were designed to be more soluble and exhibit less tendency for agglomeration with alkyl chains, in contrast to CON as HTLs.…”