In this study, we synthesized four alcohol-soluble surfactant-encapsulated polyoxometalate complexes (SEPCs) containing four tetra-n-alkyl ammonium groups, namely {[CH3(CH2)n−1]4N}4[SiW12O40] (TA-SiW12, n = 2, 4, 8, and 10), and investigated the effect of the alkyl chain length of TA-SiW12 as a cathode interlayer (CIL) on the performance of polymer solar cells (PSCs). Different alkyl chain lengths in the four TA-SiW12s resulted in different device performances. Highest power conversion efficiency (9.15%) was achieved for the PTB7:PC71BM-based PSC with TA-SiW12 (n = 8) due to its highest open circuit voltage (VOC), short circuit current (JSC), and fill factor (FF). Combined measurements of the capacitance–voltage characteristics, charge carrier mobility, and photocurrent density-effective voltage characteristics demonstrated that incorporation of TA-SiW12 (n = 8) resulted in higher built-in potential, charge carrier density, and mobility, and better charge carrier extraction as compared to that of other TA-SiW12 (n = 2, 4, and 10) in the PSCs. AFM images showed that only TA-SiW12 (n = 8) formed homogeneous, closely packed, and well-distributed grain clusters with a quasi-periodic structure on the active layer, which explains the higher JSC and FF of the PSC with TA-SiW12 (n = 8).

•Two planar VTI-based donor−acceptor 1D or 2D copolymers were designed and synthesized.•Polymer solar cells-based 1D or 2D copolymers were successfully fabricated.•A promising power conversion efficiency of 4.75% in 2D copolymer-based PSC device.Herein, π-extended vinylidenedithiophenmethyleneoxindole (VTI) unit has been incorporated to polymeric conjugated backbones affording two donor-acceptor copolymers such as one-dimensional (1D) copolymer P1 and two-dimensional (2D) copolymer P2. The VTI unit owns S⋯OC intramolecular noncovalent interactions, which is favorable for acquiring planar conjugated backbone, thus leading to enhanced semiconducting properties. Both VTI-based copolymers exhibit broad absorption profiles in the visible region. The highest occupied molecular orbital/the lowest unoccupied molecular orbital energy levels of P1 and P2 are located at −5.21/–3.50 eV, and −5.33/–3.67 eV, respectively. Bulk heterojunction solar cell-based P2 and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) blend afforded an improved power conversion efficiency (PCE) value of 4.75%. These results show that the 2D VTI-based copolymers have greater application prospect than 1D ones, and highlight the great potential of VTI unit as a building blocks for constructing high performance polymer semiconductors for PSCs.Download high-res image (242KB)Download full-size image

Correction for ‘Improving the efficiency of polymer solar cells via a treatment of methanol : water on the active layers’ by Biao Guo et al., J. Mater. Chem. A, 2016, DOI: 10.1039/c6ta04026h.

Significant improvement in the power conversion efficiency (PCE) of polymer solar cells (PSCs) has been observed when the active layer was treated with a mixture of methanol and water (M:W). For the PSCs based on ITO/PEDOT:PSS/PCDTBT:PC71BM/Al, the PCE was 6.58% when the surface of the PCDTBT:PC71BM film was treated with pure methanol. However M:W (6:1) treatment on the PCDTBT:PC71BM film could further improve the PCE to 7.44% which is even higher than the PCE values of the PSCs with LiF (6.00%) or PFN (6.88%) as a cathode interlayer. Similarly in the PSCs based on ITO/PEDOT:PSS/PTB7:PC71BM/LiF/Al, M:W (6:1) treatment on the surface of the PTB7:PC71BM film can increase the PCE to 8.47% while the PCE values of the PSCs with methanol treatment and without any treatment on the PTB7:PC71BM film are 8.14% and 7.41%, respectively. Combined contact angle measurements and X-ray photoemission spectroscopy depth profiling demonstrated that the M:W treatments resulted in a more favorable redistribution of the polymer and PC71BM in the active layer because evaporation of the solvents drove PC71BM to migrate from the interior of the blend film to the top (air) surface.

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.

•Dialkoxyl-substituted naphthodithieno [3,2-b]thiophene (NDTT)-based copolymers were synthetized and characterized.•Polymer field-effect transistors were fabricated and a high mobility up to 0.07 cm2 V−1 s−1 was obtained.•Polymer solar cells were fabricated and a power conversion efficiency of 3.54% was obtained.Herein, we report the synthesis, characterization, and their photovoltaic and field–effect properties of two dialkoxyl-substituted naphthodithieno[3,2-b]thiophene (NDTT)-based copolymers, namely P1 and P2. The NDTT-based copolymers exhibit broad absorption profiles throughout the visible spectrum up to ca. 800 nm. The copolymers have HOMO/LUMO energy levels of ca. –5.14 eV/–3.52 eV. The dialkoxyl-substituted NDTT units endow the copolymers with enhanced solution processability, and crystalline stacking thin films with small π–π distances of down to 3.59 Å. Polymer-fullerene bulk heterojunction solar cells that fabricated from a blend of P2/PC71BM using diiodooctane as a solvent additive, afforded the highest power conversion efficiency of 3.54%. Solution-processed polymer field-effect transistors based on P1 with bottom-gate bottom-contact geometry exhibited promising hole mobilities of 0.070 cm2 V−1 s−1.

Two furan-flanked diketopyrrolopyrrole copolymers, poly(3,6-difuran-2-yl-2,5-di(alkyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-altthienylenevinylene) with different alkyl side chains (PDVFs), have been synthesized and applied as a donor in polymer solar cells (PSCs). The PSC based on a blend of PDVF-8 with 2-octyldodecyl and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as an active layer has shown a better device performance than the PSC based on a blend of PDVF-10 with 2-decyltetradecyl and PC71BM. Tuning the alkyl side chains attached on the PDVFs leads to an increase of power conversion efficiency from 3.57% (PDVF-10) to 4.56% (PDVF-8) due to enhancements of short circuit current and fill factor. The effect of different alkyl side chains on the phase separation of the PDVF/PC71BM thin film has been investigated by using atomic force microscopy, transmission electron microscopy, and X-ray photoemission spectroscopy depth profiling in details. Furthermore, impedance spectroscopy was used to analyze the relationship between the phase separation of the PDVF/PC71BM blend films and the PSCs performance.

A new class of organic cathode interfacial layer (CIL) materials based on isoindigo derivatives (IID) substituted with pyridinium or sulfonate zwitterion groups were designed, synthesized, and applied in polymer solar cells (PSCs) with PTB7:PC71BM (PTB7: polythieno[3,4-b]-thiophene-co-benzodithiophene and PC71BM: [6,6]-phenyl C71-butyric acidmethyl ester) as an active layer. Compared with the control device, PSCs with an IID-based CIL show simultaneous enhancement of open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF). Systematic optimizations of the central conjugated core and side flexible alcohol-soluble groups demonstrated that isoindigo-based CIL material with thiophene and sulfonate zwitterion substituent groups can efficiently enhance the PSC performance. The highest power conversion efficiency (PCE) of 9.12%, which is 1.75 times that of the control device without CIL, was achieved for the PSC having an isoindigo-based CIL. For the PSCs with an isoindigo-based CIL, the molecule-dependent performance property studies revealed that the central conjugated core with D-A-D characteristics and the side chains with sulfonate zwitterions groups represents an efficient strategy for constructing high performance CILs. Our study results may open a new avenue toward high performance PSCs.Keywords: cathode interlayer; donor−acceptor organic molecules; isoindigo derivatives; polymer solar cell;

We present a furan-flanked DPP copolymer, poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyrrolo [3,4-c]pyrrole-1,4-dione-altthienylenevinylene} (PDVF-8), and highlight the improvement in the power conversion efficiency (PCE) of polymer solar cells (PSCs) based on the PDVF-8 as an electron donor via solvent additive and methanol treatment. When 3 vol% 1,8-diiodooctane (DIO) or 1-chloronaphthalene (CN) were used as a solvent additive to the PDVF-8:PC71BM solution in chloroform (CF), the PCE can increase from 0.79% to 3.73% or 4.26%. Methanol treatment (MT) can further enhance the PCE to 4.03% (DIO) and 4.69% (CN). The effect of the solvent additives (DIO and CN) and MT on the phase separation of the PDVF-8:PC71BM thin film has been investigated in detail using atomic force microscopy, transmission electron microscopy (TEM), TEM-energy dispersive spectroscopy and X-ray photoemission spectroscopy depth profiling.

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.

•ZnPc[S(CH2)2N(CH3)3I]8 was synthesized and successfully used as a cathode interlayer in the polymer solar cells (PSCs).•ZnPc[S(CH2)2N(CH3)3I]8 decreased work function of cathode increased hole mobility and facilitated a balance of electron and hole transport in the PSCs.A water-soluble metallophthalocyanine (MPc) derivative, 2,3,9,10,16,17,23,24-octakis(2-trimethylaminoethylsulfanyl) zincylphthalocyanine octaiodine (ZnPc[S(CH2)2N-(CH3)3I]8) was synthesized and applied in polymer solar cells (PSCs). A power conversion efficiency (PCE) of 7.06% has been obtained when the ZnPc[S(CH2)2N(CH3)3I]8 was utilized as a cathode interlayer in the PSCs based on a blend of PCDTBT (poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]) and PC71BM ([6,6]-phenyl C71 butyric acid methyl ester) as an active layer. Ultraviolet photoemission spectroscopic (UPS), atomic force microscopy (AFM), contact angle (θ) and mobility measurements demonstrated that an introduction of ZnPc[S(CH2)2N(CH3)3I]8 between active layer and cathode decreased work function of cathode, increased hole mobility and facilitated a balance of electron and hole transport in the PSCs, resulting in a simultaneous improvement of open-circuit voltage, short-circuit current and fill factor.A water-soluble metallophthalocyanine derivative ZnPc[S(CH2)2N(CH3)3I]8 was synthesized and applied in polymer solar cells (PSCs). A power conversion efficiency (PCE) of 7.06% has been obtained when the ZnPc[S(CH2)2N(CH3)3I]8 was utilized as a cathode interlayer in the PSCs based on a blend of PCDTBT and PC71BM as an active layer.

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.

We present the surface electronic and magnetic properties of half-metal La0.6Sr0.4MnO3 (LSMO) thin film modified by a simple cleaning procedure, the so-called SC1 (5 H2O, 1 NH4OH, 1 H2O2), at 85 °C for 10–40 min in ambient atmosphere. In this study, photoemission spectroscopy (XPS/UPS), X-ray absorption spectroscopy (XAS), and X-ray magnetic circular dichroism (XMCD) are used to characterize these properties of the manganites. Thanks to SC1 treatment, the work function of LSMO changes from 4.0–4.1 to 4.8–4.9 eV obtained from UPS measurements, while its surface roughness changes from 0.268 to 0.796 nm in AFM images. Combined O 1s, Mn 2p, Sr 3d, La 4d, and Mn 3s core-level XPS spectroscopy investigations suggest that Mn and Sr contents decrease at the surface and the Mn value becomes 3.7 due to SC1 treament. Mn L-edge XAS spectra of LSMO thin film demonstrate that SC1 treatment results in a removal of Mn2+ and an increase of the Mn4+ concentration. O K-edge XAS spectra further prove an enhancement of hybridization between O 2p orbitals and eg↓ of Mn 3d induced by more Mn4+. XMCD results show that SC1 treatment does not induce any drastic changes of magnetic properties of the LSMO thin film surface.

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.

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.

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.

Significant improvement in the power conversion efficiency (PCE) of polymer solar cells (PSCs) has been observed when the active layer was treated with a mixture of methanol and water (M:W). For the PSCs based on ITO/PEDOT:PSS/PCDTBT:PC71BM/Al, the PCE was 6.58% when the surface of the PCDTBT:PC71BM film was treated with pure methanol. However M:W (6:1) treatment on the PCDTBT:PC71BM film could further improve the PCE to 7.44% which is even higher than the PCE values of the PSCs with LiF (6.00%) or PFN (6.88%) as a cathode interlayer. Similarly in the PSCs based on ITO/PEDOT:PSS/PTB7:PC71BM/LiF/Al, M:W (6:1) treatment on the surface of the PTB7:PC71BM film can increase the PCE to 8.47% while the PCE values of the PSCs with methanol treatment and without any treatment on the PTB7:PC71BM film are 8.14% and 7.41%, respectively. Combined contact angle measurements and X-ray photoemission spectroscopy depth profiling demonstrated that the M:W treatments resulted in a more favorable redistribution of the polymer and PC71BM in the active layer because evaporation of the solvents drove PC71BM to migrate from the interior of the blend film to the top (air) surface.

Correction for ‘Improving the efficiency of polymer solar cells via a treatment of methanol : water on the active layers’ by Biao Guo et al., J. Mater. Chem. A, 2016, DOI: 10.1039/c6ta04026h.

In this study, we synthesized four alcohol-soluble surfactant-encapsulated polyoxometalate complexes (SEPCs) containing four tetra-n-alkyl ammonium groups, namely {[CH3(CH2)n−1]4N}4[SiW12O40] (TA-SiW12, n = 2, 4, 8, and 10), and investigated the effect of the alkyl chain length of TA-SiW12 as a cathode interlayer (CIL) on the performance of polymer solar cells (PSCs). Different alkyl chain lengths in the four TA-SiW12s resulted in different device performances. Highest power conversion efficiency (9.15%) was achieved for the PTB7:PC71BM-based PSC with TA-SiW12 (n = 8) due to its highest open circuit voltage (VOC), short circuit current (JSC), and fill factor (FF). Combined measurements of the capacitance–voltage characteristics, charge carrier mobility, and photocurrent density-effective voltage characteristics demonstrated that incorporation of TA-SiW12 (n = 8) resulted in higher built-in potential, charge carrier density, and mobility, and better charge carrier extraction as compared to that of other TA-SiW12 (n = 2, 4, and 10) in the PSCs. AFM images showed that only TA-SiW12 (n = 8) formed homogeneous, closely packed, and well-distributed grain clusters with a quasi-periodic structure on the active layer, which explains the higher JSC and FF of the PSC with TA-SiW12 (n = 8).