A series of new water/alcohol-soluble conjugated polymers (WSCPs) poly[(2,1,3-benzothiadiazole)] (PFNSO-BT), comprising identical sulfobetaine zwitterionic groups on their side chains but different conjugated main chain structures, were designed and developed as interface modification materials to improve electron collection in bulk-heterojunction polymer solar cells (PSCs), and to improve electron injection/transporting in polymer light-emitting diodes (PLEDs). The resulting WSCPs possess integrated advantages of excellent alcohol processability, interface modification functions and mobile ion free nature. The relationships between the WSCPs main chain structures and properties (including optical/electrical properties and interface modification functions in resulting devices) were investigated systematically. In PSCs, it was found that the WSCPs interface modification properties led to varying differences, but all of them can boost the photovoltaic performances of PSCs; encouragingly, a high power conversion efficiency (PCE) of 8.74% could be achieved. In PLEDs, the interface modification functions of the WSCPs strongly depend upon their conjugated main chain structures. The WSCPs should possess suitable energy levels to match well with the light-emitting layer (EML), even though the electron injection from metal cathode was efficient. Our results show promising potentials of WSCPs as interface modification layers in organic/polymer optoelectronic devices, and provide new insights for the development of new interface modification materials in the future. † Electronic supplementary information (ESI) available: Experimental details including the synthesis and characterization of target polymers, device fabrication and measurements, external quantum efficiency (EQE) spectra as well as J-V characteristics of single charge carrier devices. See Scheme 1 (a) Device architecture of PSCs and PLEDs used in this study, as well as chemical structures of WSCPs with identical pendant zwitterionic groups but different conjugated main chains developed in this study. (b) Chemical structures of narrow-band-gap polymer PTB7, electron acceptor PC 71 BM, green-emitters P-PPV and F8BT employed in this study.

Conjugated polyelectrolytes (CPEs) have attracted considerable attention in recent years due to their signifi cant application potential in organic optoelectronic devices [1][2][3][4] and chemo-/ bio-sensors. [ 5 , 6 ] Their pendant ionic groups offer them unique solubility in high polarity solvents, which is orthogonal to most of the commonly used conjugated polymer active materials, and allow the fabrication of solution-processed multilayer devices to maximize the performance. Moreover, it was proved that the CPE's pendant polar groups also can effectively improve electron injection from high work-function metals (such as Al, Ag, Au), which open a way to achieve all printable roll-to-roll polymer based organic electronic devices and the fi rst fully solution processed polymer light-emitting diodes (PLEDs) have been realized based on them. [ 7 ] Despite their application potential in devices, most of CPE contain mobile counter-ions, which can migrate into the emission layer (EML) and may affect the longterm stability of devices. [ 8 ] In addition, the response time of the devices and the mobility of the CPE are also greatly infl uenced by the nature of their counter-ions. [ 9 , 10 ] To overcome these, one alternative way is to develop water/alcohol soluble conjugated polymers with neutral high polarity pendant groups. [ 11 ] However, it is very challenging to get highly water/alcohol soluble neutral conjugated polymers due to that conjugated polymers always contain a very rigid, highly hydrophobic main chain and the polarity of nonionic pendant groups is usually not high enough to ensure them good solubility in water/alcohol. Zwitterionic polyelectrolytes contain both anionic and cationic groups, which usually exhibit good water/alcohol solubility and there is no mobile counter-ions among them. [ 12 ] Moreover, recent research has shown that zwitterionic groups can also enhance the electron injection from high work-function metal cathodes as those traditional ionic groups (such as ammonium) or other high polarity groups (such as amino, diethanol amino etc.) [ 13 ] Thus, conjugated zwitterionic polyelectrolytes (CZPEs) could be the promising candidate as electron transporting/injecting layer (ETL) for PLEDs, combining the advantages of good charge transporting ability, mobile ions free nature and good water/alcohol solubility, etc. Although there are rarely researches reported on the using of CZPEs for organic electronic devices.Herein, we report the development of a new CZPE, poly[9,9-bis((N-(3-sulfonate-1-propyl)-N,N-diethylammonium)-hexyl)-2,7-fl uorene] (PF 6 NSO), with different quaternized degrees and their precursor poly[9,9-bis(6-(N,N-diethylamino)-hexyl)fl uorene] (PF 6 N) as highly effi cient electron injecting/ transporting materials for PLEDs. Our results show that the zwitterionic groups among PF 6 NSO not only enhance the alcohol solubility of the polymers, but also signifi cantly enhance their electron injection ability, which are promising candidates of new interface modifi cation layer for orga...

A series of amino N‐oxide functionalized polyfluorene homopolymers and copolymers (PNOs) are synthesized by oxidizing their amino functionalized precursor polymers (PNs) with hydrogen peroxide. Excellent solubility in polar solvents and good electron injection from high work‐function metals make PNOs good candidates for interfacial modification of solution processed multilayer polymer light‐emitting diodes (PLEDs) and polymer solar cells (PSCs). Both PNOs and PNs are used as cathode interlayers in PLEDs and PSCs. It is found that the resulting devices show much better performance than devices based on a bare Al cathode. The effect of side chain and main chain variations on the device performance is investigated. PNOs/Al cathode devices exhibit better performance than PNs/Al cathode devices. Moreover, devices incorporating polymers with para‐linkage of pyridinyl moieties exhibit better performance than those using polymers with meta‐linked counterparts. With a poly[(2,7‐(9,9‐bis(6‐(N,N‐diethylamino)‐hexyl N‐oxide)fluorene))‐alt‐(2,5‐pyridinyl)] (PF6NO25Py) cathode interlayer, the resulting device exhibits a luminance efficiency of 16.9 cd A−1 and a power conversion efficiency of 6.9% for PLEDs and PSCs, respectively. These results indicate that PNOs are promising new cathode interlayers for modifying a range of optoelectronic devices.

A new metal‐oxide‐based interconnecting layer (ICL) structure of all‐solution processed metal oxide/dipole layer/metal oxide for efficient tandem organic solar cell (OSC) is demonstrated. The dipole layer modifies the work function (WF) of molybdenum oxide (MoO x ) to eliminate preexisted counter diode between MoO x and TiO2. Three different amino functionalized water/alcohol soluble conjugated polymers (WSCPs) are studied to show that the WF tuning of MoO x is controllable. Importantly, the results show that S‐shape current density versus voltage (J–V) characteristics form when operation temperature decreases. This implies that thermionic emission within the dipole layer plays critical role for helping recombination of electrons and holes. Meanwhile, the insignificant homotandem open‐circuit voltage (V oc) loss dependence on dipole layer thickness shows that the quantum tunneling effect is weak for efficient electron and hole recombination. Based on this ICL, poly(3‐hexylthiophene) (P3HT)‐based homotandem OSC with 1.20 V V oc and 3.29% power conversion efficiency (PCE) is achieved. Furthermore, high efficiency poly(4,8‐bis(5‐(2‐ethylhexyl)‐thiophene‐2‐yl)‐benzo[1,2‐b54,5‐b9]dithiophene‐alt alkylcarbonylthieno[3,4‐b]thiophene) (PBDTTT‐C‐T)‐based homotandem OSC with 1.54 V V oc and 8.11% PCE is achieved, with almost 15.53% enhancement compared to its single cell. This metal oxide/dipole layer/metal oxide ICL provides a new strategy to develop other qualified ICL with different hole transporting layer and electron transporting layer in tandem OSCs.

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