Youchun Chen

Electrochemical route to fabricate film-like conjugated microporous polymers and application for organic electronics.

Film-like conjugated microporous polymers (CMPs) are fabricated by the novel strategy of carbazole-based electropolymerization. The CMP film storing a mass of counterions acting as an anode interlayer provides a significant power-conversion efficiency of 7.56% in polymer solar cells and 20.7 cd A(-1) in polymer light-emitting diodes, demonstrating its universality and potential as an electrode interlayer in organic electronics.

π‐Conjugated Microporous Polymer Films: Designed Synthesis, Conducting Properties, and Photoenergy Conversions

Conjugated microporous polymers are a unique class of polymers that combine extended π-conjugation with inherent porosity. However, these polymers are synthesized through solution-phase reactions to yield insoluble and unprocessable solids, which preclude not only the evaluation of their conducting properties but also the fabrication of thin films for device implementation. Here, we report a strategy for the synthesis of thin films of π-conjugated microporous polymers by designing thiophene-based electropolymerization at the solution–electrode interface. High-quality films are prepared on a large area of various electrodes, the film thickness is controllable, and the films are used for device fabrication. These films are outstanding hole conductors and, upon incorporation of fullerenes into the pores, function as highly efficient photoactive layers for energy conversions. Our film strategy may boost the applications in photocatalysis, energy storage, and optoelectronics.

Porous Organic Polymer Films with Tunable Work Functions and Selective Hole and Electron Flows for Energy Conversions

Organic optoelectronics are promising technologies for energy conversion. However, the electrode interlayer, a key material between active layers and conducting electrodes that controls the transport of charge carriers in and out of devices, is still a chemical challenge. Herein, we report a class of porous organic polymers with tunable work function as hole- and electron-selective electrode interlayers. The network with organoborane and carbazole units exhibits extremely low work-function-selective electron flow; while upon ionic ligation and electro-oxidation, the network significantly increases the work function and turns into hole conduction. We demonstrate their outstanding functions as anode and cathode interlayers in energy-converting solar cells and light-emitting diodes.

A water-soluble metallophthalocyanine derivative as a cathode interlayer for highly efficient polymer solar cells

A novel organic small molecule water-soluble poly-N-alkylpyridine substitued metallophthalocyanine derivative VOPc(OPyCH3I)8, namely 2,3,9,10,16,17,23,24-octakis-[N-methyl-(3-pyridyloxy)] vanadylphthalocyanine iodide (1 : 8), was synthesized and applied in polymer solar cells (PSCs). Notably, a power conversion efficiency (PCE) of 8.12% for the working area of 2 × 2 mm2 and a PCE of 7.23% for the working area of 4 × 4 mm2 have been achieved in the PSCs with this molecule as a cathode interlayer. They are comparable with the higher values of PCE of the PSCs reported currently, indicating that VOPc(OPyCH3I)8 is a new promising candidate as a good cathode interlayer for highly efficient PSCs.

Highly efficient polymer solar cells based on a universal cathode interlayer composed of metallophthalocyanine derivative with good film-forming property

A new cathode interlayer (CIL) material metallophthalocyanine (MPc) derivative 1,4,8,11,15,18,22,25-octaoctyloxy-2,3,9,10,16,17,23,24-octa-[N-methyl-(3-pyridyloxy)] zinc-ylphthalocyanine iodide (1 : 8) (ZnPc(OC8H17OPyCH3I)8) was synthesized and applied in polymer solar cells (PSCs) based on PTB7:PC71BM (PTB7 = thieno[3,4-b]thiophene/benzodithiophene, PC71BM = [6,6]-phenyl C71-butyric acidmethyl ester), P3HT:PC61BM (P3HT = poly(3-hexylthiophene), PC61BM = [6,6]-phenyl C61-butyric acidmethyl ester) or PCDTBT:PC71BM (PCDTBT = poly[N-9′′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]) as an active layer. As a result, power conversion efficiency (PCE) values of the PSCs were 8.52%, 4.02% and 6.88%, respectively, which are much higher than those of corresponding PSCs with the Al-only cathode. It indicates that ZnPc(OC8H17OPyCH3I)8 is a new promising candidate as a universal CIL for highly efficient PSCs. Compared to VOPc(OPyCH3I)8 (2,3,9,10,16,17,23,24-octakis-[N-methyl-(3-pyridyloxy)] vanadylphthalocyanine iodide (1 : 8)), the PSC with ZnPc(OC8H17OPyCH3I)8 as a CIL has higher short-circuit current and fill factor because ZnPc(OC8H17OPyCH3I)8 can form a better, denser, and more uniform film on the active layer than VOPc(OPyCH3I)8 as demonstrated by atomic force microscopy (AFM), energy-dispersive spectrum mapping on scan electron microscopy (SEM-EDS mapping) and contact angle measurements.

N-type cathode interlayer based on dicyanomethylenated quinacridone derivative for high-performance polymer solar cells

A new π-conjugated electrolyte bis(dicyanomethylene)-quinacridone with two octyl-pyridium (DCNQA-PyBr) has been synthesized and employed as a solution-processed cathode interlayer (CIL) for polymer solar cells (PSCs). The devices exhibited simultaneously increased open-circuit voltage (Voc), short-circuit current (Jsc) and fill factor (FF). Overall, the PSCs with PCDTBT (poly[N-9′′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]) as a donor and PC71BM ([6,6]-phenyl C71-butyric acid methyl ester) as an acceptor incorporating a 13 nm DCNQA-PyBr interlayer exhibit a power conversion efficiency (PCE) of 6.96%, which is 1.3 times of that of the Al-only device. Most importantly, compared to the reference π-conjugated electrolyte QA-PyBr, DCNQA-PyBr shows much improved electron transport ability and conductivity. As a result, the DCNQA-PyBr based devices only show a slight decrease in electron transport upon increasing the thickness of the CIL, thus allowing a high PCE with a wide CIL thickness range from 5 nm to 40 nm. Furthermore, introducing DCNQA-PyBr as a CIL into the devices based on P3HT:PC61BM (P3HT = poly(3-hexylthiophene), PC61BM = [6,6]-phenyl C61-butyric acid methyl ester) and PTB7:PC71BM (PTB7 = polythieno[3,4-b]-thiophene-co-benzodithiophene) also leads to significantly enhanced device performance, showing high PCEs of 3.91% and 8.23%, respectively. These results confirm DCNQA-PyBr to be a promising CIL material for solution-processed large-area PSCs.

Metallophthalocyanine derivatives utilized as cathode interlayers for polymer solar cells: a practical approach to prepare a uniform film

Three metallophthalocyanine derivatives: 2,3,9,10,16,17,23,24-octakis-[N-ethyl-(3-pyridyloxy)]vanadylphthalocyanine bromine (1 : 8) (VOPc(OPyC2H5Br)8), 2,3,9,10,16,17,23,24-octakis-[N-butyl-(3-pyridyloxy)]vanadylphthalocyanine bromine (1 : 8) (VOPc(OPyC4H9Br)8) and 2,3,9,10,16,17,23,24-octakis-[N-hexyl-(3-pyridyloxy)]vanadylphthalocyanine bromine (1 : 8) (VOPc(OPyC6H13Br)8) were synthesized and applied in polymer solar cells (PSCs) based on PTB7:PC71BM (PTB7 = thieno[3,4-b]thiophene/benzodithiophene, PC71BM = [6,6]-phenyl C71-butyric acidmethyl ester) as an active layer. As a result, the highest power conversion efficiency (PCE) value of the PSCs is 7.99% for the device with VOPc(OPyC2H5Br)8 as a cathode interlayer. Although increasing the alkyl side chains attached to the pyridine functional groups of phthalocyanine leads to a slight decrease of PCE, VOPc(OPyC6H13Br)8 can form a better, denser and more uniform film on the active layer as demonstrated by atomic force microscopy, energy dispersive spectrum mapping and contact angle measurements.

Anode Engineering of Highly Efficient Polymer Solar Cells Using Treated ITO

ITO substrates were treated with organic solvent cleaning(OSC), SC1 treatment[V(NH4OH):V(H2O2): V(H2O)=1:1:5], O2 plasma and UV ozone, respectively. Combined investigations of atom force microscopy(AFM), water contact angle measurements, ultraviolet photoemission spectroscopy(UPS) and X-ray photoemission spectroscopy(XPS) demonstrated that UV ozone treatment could give rise to the smoothest surface, the most hydrophilic property and the highest work function(WF) of ITO due to the removal of hydrophobic C―O impurity from the ITO surface and the enrichments of more oxygen on the ITO surface. When PEDOT:PSS film[(poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate)] was deposited on the ITO substrates treated with UV ozone, it showed a lower root-mean- square roughness in AFM images, a higher transmission in UV-Vis transmission spectra and a higher WF in UPS spectra than the PEDOT:PSS films deposited on the ITO substrates treated by other three methods. As a result, the power conversion efficiency of polymer solar cells(PSCs) based on PTB7:PC71BM as an active layer and ITO treated by UV ozone as an anode can reach 8.48% because of the simultaneously improved short circuit current, open circuit voltage and fill factor compared to the PSCs with ITO treated with other three methods.

A naphthodithieno[3,2-b]thiophene-based copolymer as a novel third component in ternary polymer solar cells with a simultaneously enhanced open circuit voltage, short circuit current and fill factor

A dialkoxyl-substituted naphthodithieno[3,2-b]thiophene-based copolymer (PV12) was applied as a third component for ternary polymer solar cells (PSCs) based on PCDTBT1−x:PV12x:PC71BM. In Al-only ternary PSCs with x = 0.15, a power conversion efficiency (PCE) of 6.73% was achieved due to simultaneous enhancement in the open circuit voltage, short circuit current and fill factor, which is much higher than the PCE of 5.28% for Al-only binary PSCs based on PCDTBT:PC71BM and 2.93% for Al-only binary PSCs based on PV12:PC71BM. The PCE reached 7.69% when IIDTh-NSB as a cathode interlayer was introduced between the ternary active layer and Al. Ultraviolet photoemission spectroscopy measurements demonstrated a cascade-type energy level alignment at the ternary PCDTBT(D1)/PV12(D2)/PC71BM(A) junction. As a result, the voltage limitation was overcome at the D1/D2/A junction. Ultraviolet-visible absorption and external quantum efficiency spectra showed that PV12 had complementary absorption to PCDTBT in the solar spectrum. Atomic force microscopy and transmission electron microscopy images showed that the morphology and phase separation of the active layer were optimized by adding PV12. Photoluminescence spectral investigations suggested that the Forster resonance energy transfer from PCDTBT to PV12 occurred in the ternary PSCs under illumination. Finally, the PCEs of the ternary PSCs are not as sensitive to the thickness of the active layer as those of the binary PSCs, which is important for the roll-to-roll coating processing of organic photovoltaic modules.