Despite the excellent work function adjustability of conjugated polyelectrolytes (CPEs), which induce a vacuum level shift via the formation of permanent dipoles at the CPE/metal electrode interface, the exact mechanism of electron injection through the CPE electron transport layer (ETL) remains unclear. In particular, understanding the ionic motion within the CPE ETLs when overcoming the sizable injection barrier is a signifi cant challenge. Because the ionic functionality of CPEs is a key component for such functions, a rigorous analysis using highly controlled ion density (ID) in CPEs is crucial for understanding the underlying mechanism. Here, by introducing a new series of CPEs with various numbers of ionic functionalities, energy level tuning at such an interface can be determined directly by adjusting the ID in the CPEs. More importantly, these series CPEs indicate that two different mechanisms must be invoked according to the CPE thickness. The formation of permanent interfacial dipoles is critical with respect to electron injection through CPE ETL (≤ 10 nm, quantum mechanical tunneling limit), whereas electron injection through thick CPE ETL (20-30 nm) is dominated by the reorientation of the ionic side chains under a given electric fi eld. Metal ActiveE vac M eff e µ ID CPE LUMO HOMO

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...

This paper reports an improved solar cell performance of 8.6% by incorporation of N-doped multiwall carbon nanotubes (N-MCNTs) into BHJ solar cells composed of PTB7 and PC71BM. It was demonstrated for the first time that incorporation of N-MCNTs leads to not only increased nanocrystallite sizes but also smaller phase-separated domain sizes of both PTB7 copolymers and PC71BM from X-ray scattering study. The results show that N-MCNTs could serve as both exciton dissociation centers and charge transfer channels. The enhanced charge dissociation probabilities and effective charge carrier lifetime in the active layer material offer evidence to support the conclusion that N-MCNTs facilitated charge separation and transport.

In this perspective article, we discuss the development of organic photovoltaic (OPVs) solar cells. Our focus will be on discussing the development of new donor polymers and device technologies, which resulted in enormous progress in OPV performances with power conversion efficiencies (PCEs) of 8-9%. However, for the wide spread usage of OPVs, high module efficiencies (>10%) and lifetimes suitable for commercial applications are required. To achieve such goals, interdisciplinary advances in the development of new light-harvesting materials, the improvement of device structures, and the development of cost effective device processing methods are crucial. In particular, new donor polymers overcoming the drawbacks of current polymer solar cells can play an important role to further improve the PCEs and device stability. This perspective article addresses the polymer design criteria that have been distilled out from the research of the past 20 years: energy level matching, nano-morphology of polymer/acceptor blend films, local dipole moments of the polymer chains, and stability. Also, we introduce representative donor polymers and describe the research progress in the polymers development to move beyond certain milestones. We emphasize the importance of the synergetic research efforts in developing new materials, such as the design of new polymers with improved physical properties, the development of device technologies and a fundamental understanding of OPV mechanisms, which will help to continuously enhance the performance of OPVs.

We demonstrate highly sensitive and selective potassium ion detection against excess sodium ions in water, by modulating the interaction between the G-quadruplex-forming molecular beacon aptamer (MBA) and cationic conjugated polyelectrolyte (CPE). The K(+)-specific aptamer sequence in MBA is used as the molecular recognition element, and the high binding specificity of MBA for potassium ions offers selectivity against a range of metal ions. The hairpin-type MBA labeled with a fluorophore and quencher at both termini undergoes a conformational change (by complexation with CPEs) to either an open-chain form or a G-quadruplex in the absence or presence of K(+) ions. Conformational changes of MBA as well as fluorescence (of the fluorophore in MBA) quenching or amplification via fluorescence resonance energy transfer from CPEs provide clear signal turn-off and -on in the presence or absence of K(+). The detection limit of the K(+) assays is determined to be ~1.5 nM in the presence of 100 mM Na(+) ions, which is ~3 orders of magnitude lower than those reported previously. The successful detection of 5'-adenosine triphosphate (ATP) with the MBA containing an ATP-specific aptamer sequence is also demonstrated using the same sensor scheme. The scheme reported herein is applicable to the detection of other kinds of G-rich aptamer-binding chemicals and biomolecules.