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Porphyrin and its derivatives play important roles in natural energy conversion applications. In this work, we designed and synthesized three novel acceptor–donor–acceptor (A–D–A) type small molecules (namely Por-Cu-IC, Por-Cu-ICF and Por-Cu-ICFF) with the Cu(II)-porphyrin as the central electron-donating core and fluorinated 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile as the electron-withdrawing end groups. These new molecules show broad absorption spectra from 300 to 900 nm with strong intramolecular charge transfer absorption spectra at around 800 nm, and an optical bandgap of about 1.4 eV. Organic solar cells (OSCs) based on these new molecules as non-fullerene electron acceptors achieved power conversion efficiencies from 0.5% to 2.44%. The OSCs were characterized by several techniques, including density functional theory (DFT), space-charge limited current (SCLC), photoluminescence spectra (PL) and atomic force microscopy (AFM). These results demonstrate a systematic study of Cu(II)-porphyrin molecules, which could be used to design molecules for use in organic electronics.

Two novel truxene-based conjugated porous polymers (CPPs), Tr-F8 and Tr-F3N with octyl and amino side chains, were designed for photocatalytic hydrogen evolution. The introduction of hydrophilic amino side chains significantly improved the wettability of Tr-F3N, resulting in a largely enhanced hydrogen evolution rate (HER) in comparison with that of hydrophobic octyl functionalised Tr-F8. Density functional theory simulation indicates that the amino groups can enhance the interaction between H2O molecules and photocatalysts at a molecular level, resulting in more efficient charge transfer. As a result, a high HER over 500 μmol h−1 g−1 was achieved for Tr-F3N with triethanolamine as the sacrificial electron donor in the absence of co-catalysts. Moreover, a positive correlation between the wettability and HER of CPPs was obtained through structural evolution of CPPs by increasing their amino group density. Our work formulates a novel design guideline for organic photocatalysts for hydrogen evolution, which can be used as a universal strategy to improve the photocatalytic activity of organic photocatalysts.

Perylene diimide (PDI) based semiconductors with high mobility are promising electron-transporting materials (ETMs), which are used to fabricate polymer solar cells (PSCs) using roll-to-roll (R2R) processing. However, PDI-based molecular semiconductors have a strong tendency to aggregate, which hinders their use as ETMs in the fabrication of high-performance thin-film devices. Additionally, multi-layer organic opto-electronic devices require that the materials for different layers should possess orthogonal solubility. Here, we develop an in situ polymerisation method to successfully prepare ion-containing PDI-based polyelectrolytes with good water/alcohol solubility, which can enable high-performance PSCs. The doping behaviour, self-assembling and charge-transporting properties of these polyelectrolytes can be fine-tuned by their anions, which allows the fabrication of high-quality and high-mobility electron-transporting thin films for PSCs. PSCs with these polyelectrolytes can maintain high power conversion efficiencies of over 8% when the thickness of the polyelectrolyte is up to 50 nm, which offers a remarkable processing window for the mass-fabrication of PSCs using R2R techniques. Our findings on the structure–property–performance relationships of these polyelectrolytes provide insights and guidelines for the design of high-performance n-type polyelectrolytes for organic opto-electronic devices.

N-type conjugated polyelectrolytes (CPEs) are promising electron transport materials (ETMs) in high-performance polymer solar cells (PSCs). The regulation of the counterions of CPEs can efficiently tune the properties of CPEs as well as their photovoltaic performance. In this contribution, we report a series of counterion-tunable n-type CPEs for the interface engineering of polymer solar cells, and the size, species and substituent groups of the counterions are discussed. The size of counterions had a great impact on the alcohol solubility and photophysical properties of CPEs. Besides, the self-doping behaviors of these CPEs are also highly correlated with their counterion species. Moreover, the charge transport and electrode modification study results show that the counterion species and their substituent groups are critical to the electron mobilities and electrode modification ability of these CPEs as well as their performance in PSCs. PSCs with these CPEs as ETMs can deliver high power conversion efficiency (PCE) up to 10.5%, and over 9.5% PCE can be maintained even when these CPEs are used as thick (80 nm) ETMs, indicating great potential of using these CPEs as thickness-insensitive ETMs for the fabrication of future large-area PSCs using roll-to-roll techniques.

A polymer with tailored chemical functionality was introduced as a processing additive to control the film formation of the CH3NH3PbI3 perovskite structure, leading to enhanced photovoltaic performance in a PEDOT:PSS/perovskite/PCBM-based planar heterojunction solar cell under optimized conditions. By adjusting the polymer doping content and the processing solvent, the grain size, film coverage and the optical properties of the perovskite films can be effectively tuned. At optimized conditions, the planar heterojunction solar cell composed of a thin layer of perovskite–polymer film (∼50 nm) exhibits an average PCE of 6.16% with a Voc of 1.04 V, a Jsc of 8.85 mA cm−2 and a FF of 0.65, which are much higher than those of the control device with a pristine perovskite film. The higher performance was attributed to improved morphology and interfaces of the perovskite–polymer films, which reduced the undesired contact between PEDOT:PSS and PCBM and minimized the shunting paths in the device. In addition, since the fabrication process for the perovskite solar cells can be performed at low temperature, flexible cells built on plastic substrates can therefore be realized with a PCE of 4.35%.

A new amino-functionalized polymer, PN4N, was developed and applied as an efficient interlayer to improve the cathode interface of fullerene/perovskite (CH3NH3PbIxCl3−x) planar heterojunction solar cells. The PN4N polymer is soluble in IPA and n-BuOH, which are orthogonal solvents to the metallohalide perovskite films, and therefore they can be spuncast on the heterojunction layer before the deposition of the metal cathode. This simple modification of the cathode interface showed a remarkable enhancement of power conversion efficiency (PCE) from 12.4% to 15.0% and also reduced the hysteresis of photocurrent. We also found that conventional water–methanol-soluble polymer interlayer, such as PFN, was incompatible with the perovskite films because of the small molecular size of aprotic solvent such as MeOH, which could decompose the perovskite films to PbI2, resulting in considerably lower solar cell performance. This study provides new design guidelines for efficient interfacial materials and also demonstrates that interface engineering could be a key strategy to improve perovskite solar cells.

Correction for ‘Highly efficient fullerene/perovskite planar heterojunction solar cells via cathode modification with an amino-functionalized polymer interlayer’ by Qifan Xue et al., J. Mater. Chem. A, 2014, 2, 19598–19603.

To develop environmentally friendly solvent processed high performance polymer solar cells (PSCs), an alcohol soluble narrow-band-gap conjugated polymer PCDTBT-N and an alcohol soluble C70 fullerene derivative PC71BM-N, which were functionalized with pendant tertiary amino groups, were developed and used as active layers in PSCs and as buffer layers in metal–semiconductor interfaces. Though solar cells with active layers containing amino groups showed no photovoltaic properties regardless of the processing conditions, both PCDTBT-N and PC71BM-N performed well as buffer layers to improve electron collection in PSCs. Space charge limited current (SCLC), field effect transistor (FET) and cyclic voltammetry (CV) studies revealed that the amino groups act as hole traps and disable hole transport in active layers. Moreover, ultraviolet photoelectron spectroscopy (UPS) indicates electronic structure changes and Fermi level shifts upon complexation of amino groups and the fullerene core, which may diminish the electron-accepting capacity of fullerenes, and may potentially provide a different kind of hole trap in the devices. The underlying mechanisms of the puzzling behavior of PCDTBT-N and PC71BM-N in different layers of PSCs were studied by numerical simulation, which indicates that hole traps distributed in the BHJ layer reduce device performance, conversely hole traps concentrated near the metal electrode can improve device performance. Besides, the formation of an amino group:C70 complex is another important cause of the performance improvements of the resulting solar cells using PCDTBT-N and PC71BM-N as buffer layers, due to the reduced transport loss for efficient electron collection through the n-doping of PC71BM at the interface of the buffer layer and the active layer.