Changyun Jiang

An inverted organic solar cell employing a sol-gel derived ZnO electron selective layer and thermal evaporated MoO3 hole selective layer

We reported an efficient inverted bulk-heterojunction [regioregular of poly(3-hexylthiophene): (6,6)-phenyl C61 butyric acid methyl ester] solar cell with a highly transparent sol-gel derived ZnO film as electron selective layer and MoO3 as hole selective layer. By modifying the precursor concentration of sol from 0.75 to 0.1M, the optical transmittance of ZnO film increases from 75% to 95%. This improvement in transmittance increases the short-circuit density of inverted solar cell from 5.986 to 8.858 mA/cm2 without sacrificing the open-circuit voltage and fill factor of the device. We also demonstrated that the device incorporated with MoO3 has a larger open-circuit voltage and fill factor than the device without MoO3. Power conversion efficiency of 3.09% was achieved under simulated AM 1.5G illumination of 100 mW/cm2.

High-bendability flexible dye-sensitized solar cell with a nanoparticle-modified ZnO-nanowire electrode

We report a high-bendability flexible dye-sensitized solar cell (DSSC) based on a ZnO-nanowire photoelectrode, which was fabricated on polyethylene terephtalate/indium tin oxide substrate by low-temperature hydrothermal growth. Nanowire morphology shows preferable in crack resistance due to its efficient release of bending stress. The ZnO-nanowire film can be bended to an extreme radius of 2mm with no crack observed. Flexible DSSCs based on this kind of ZnO-nanowire photoelectrodes showed good bending stability. With a ZnO-nanoparticle modification on the nanowires, the flexible DSSC fabricated showed a much improved power conversion efficiency. Meanwhile, the good bendablility of this nanoparticle-modified nanowire electrode is maintained. The results demonstrate that high quality ZnO nanowires fabricated by the low-temperature method is promising for efficient and flexible plastic solar cells.

Efficient tandem organic solar cells with an Al/MoO3 intermediate layer

We report efficient tandem organic solar cells with an Al and MoO3 intermediate layer. Such an intermediate layer with optimized thickness (1 nm Al and 15 nm MoO3) has high transparency (∼98% in the range from 350 to 900 nm) and efficient charge collections to realize electric connection in series. For polymer-small molecule tandem cell, due to the summation (1.01 V) of the open-circuit voltages of individual cells and a short-circuit current density of 6.05 mA/cm2, a power conversion efficiency (PCE) of 2.82% was obtained under 100 mW/cm2 illumination, which is larger than either of the individual cells. The PCE reached 3.88% when the tandem cell was illuminated under 300 mW/cm2. Additionally, we applied Al/MoO3 intermediate layer to realize a solution-processed polymer tandem cell with a high PCE (2.23%). The thick MoO3 (15 nm) provides a complete protection of the prior-deposited polymer layer from dissolving during the top cell polymer coating.

High efficiency planar Si/organic heterojunction hybrid solar cells

We present an efficient hybrid solar cell based on poly (3,4-ethylene-dioxythiophene):polystyrenesulfonate and planar Si with (100) and (111) orientations. The effect of Si surface native oxide on cell performance is studied. Compared to cell with hydrogen-terminated Si surface, the cell with oxygen-terminated Si surface reveals a 530-fold increase in power conversion efficiency (PCE) from 0.02% to 10.6%. The formation of SiOx-Si bonds poses a net positive surface dipole which leads to a favorable band alignment for charge separation. However, thicker oxide degrades cell performance due to higher series resistance. This study demonstrates the highest PCE reported to-date in this field.

An oleic acid-capped CdSe quantum-dot sensitized solar cell

In this letter, we report an oleic acid (OA)-capped CdSe quantum-dot sensitized solar cell (QDSSC) with an improved performance. The TiO2/OA-CdSe photoanode in a two-electrode device exhibited a photon-to-current conversion efficiency of 17.5% at 400 nm. At AM1.5G irradiation with 100 mW/cm2 light intensity, the QDSSCs based on OA-capped CdSe showed a power conversion efficiency of about 1%. The function of OA was to increase QD loading, extend the absorption range and possibly suppress the surface recombination.

Highly efficient Si-nanorods/organic hybrid core-sheath heterojunction solar cells

We report a hybrid solar cell based on well-aligned crystalline silicon nanorods (SiNRs) and an organic semiconductor, 2,2′,7,7′-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (Spiro-OMeTAD), in a core-sheath heterojunction structure. The device is formed by spin coating Spiro-OMeTAD on SiNRs array fabricated by electroless chemical etching. A silver grid on a conductive poly (3,4-ethylene-dioxythiophene): polystyrenesulfonate layer is used as the top transparent anode. A power conversion efficiency of 10.3% has been obtained for a 1-cm2 cell with 0.35-µm long SiNRs. The high efficiency and simple solution process used suggest that such devices are promising for developing low cost and high efficiency SiNRs/organic solar cells.

Development of Inverted Organic Solar Cells with TiO2 Interface Layer by Using Low-Temperature Atomic Layer Deposition

Organic solar cells (OSCs) with inverted structure have attracted much attention in recent years because of their improved device air stability due to the use of stable materials for electrodes and interface layers. In this work, TiO(2) films, fabricated using low temperature (e.g., 130-170 °C) atomic layer deposition (ALD) on ITO substrates, are used as electron selective interface layers to investigate inverted OSCs. It is found that though the as-deposited TiO(2) films are high resistive due to the presence of oxygen defects, the defects can be significantly reduced by light soaking. PV cells with 15-nm-thick amorphous-TiO(2) layers fabricated at low temperature show better performance than those with poly crystal TiO(2) with same thickness deposited at 250 °C. The low temperature ALD-grown TiO(2) films are dense, stable and robust with capability of conformal coating on nanostructural surfaces, showing a promising interface layer for achieving air-stable plastic OSCs with roll-to-roll mass production potential.

High-efficiency si/polymer hybrid solar cells based on synergistic surface texturing of Si nanowires on pyramids.

An efficient Si/PEDOT:PSS hybrid solar cell using synergistic surface texturing of Si nanowires (SiNWs) on pyramids is demonstrated. A power conversion efficiency (PCE) of 9.9% is achieved from the cells using the SiNW/pyramid binary structure, which is much higher than similar cells based on planar Si, pyramid-textured Si, and SiNWs. The PCE is the highest reported to-date for hybrid cells based on Si nanostructures and PEDOT.

New iridium complex as high-efficiency red phosphorescent emitter in polymer light-emitting devices

A new heteroleptic iridium complex Ir(1-piq)2pt with 1-phenylisoquinoline and 3-(pyridin-2′-yl)-1H-1,2,4-triazole was synthesized and characterized. The complex was incorporated into phosphorescent polymer light-emitting devices using polyhedral oligomeric silsesquioxane-terminated polyfluorene (PFO-poss) as a host polymer doped with 30% of electron transport materials 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD). Red electrophosphorescence was observed with a peak emission at 605 nm. The highest-efficiency polymer light-emitting diode was achieved with PFO-poss doped with 2% Ir(1-piq)2pt. An external quantum efficiency of 10.4% and a luminous efficiency of 9.4 cd A−1 were obtained at 10.8 mA cm−2. These values were found to be 7.67% and 5.99 cd A−1 at 100 mA cm−2.

Improved adhesion of interconnected TiO2 nanofiber network on conductive substrate and its application in polymer photovoltaic devices

The application of electrospun ceramic nanofibers is limited in electronic devices due to their poor adhesion on conductive substrates. In this regard, a simple method is developed by inserting an ultrathin surface treatment layer between TiO2 nanofiber mats and a conductive substrate to enhance interfacial adhesion. Polymer hybrid photovoltaic devices based on the TiO2 nanofibrous network were fabricated and investigated. Improved device performance was obtained by TiCl4 treatment and interfacial modification for the TiO2 nanofibers, as compared to those without any treatment.