Shengping Ruan

Role of tungsten oxide in inverted polymer solar cells

Tungsten oxide (WO3) was inserted as an anode interfacial layer between the photoactive layer and top electrode in inverted polymer solar cells (PSCs) with nanocrystalline titanium dioxide as an electron selective layer. The device with WO3 exhibited a remarkable improvement in power conversion efficiency compared with that without WO3, which indicated that WO3 efficiently prevented the recombination of charge carriers at the organic/top electrode interface. The dependence of the device performances on WO3 film thickness and different top metal electrodes was investigated. Transparent inverted PSCs with thermally evaporable Ag/WO3 as a transparent anode were also investigated when introducing a WO3 buffer layer.

Performance improvement of inverted polymer solar cells with different top electrodes by introducing a MoO3 buffer layer

Molybdenum trioxide (MoO3) was inserted between the active layer and top electrode in inverted polymer solar cells (PSCs) with nanocrystalline titanium dioxide as an electron selective layer. The performances of structurally identical PSCs with different top electrodes (Au, Ag, and Al) were investigated and compared. The interface between MoO3 and different metals was studied by x-ray photoelectron spectroscopy. The results showed that the performances of devices with different metals are greatly improved due to the incorporation of MoO3 and the open-circuit voltage of devices is relatively insensitive to the choice of the anode metal when MoO3 is introduced.

TiO2 based metal-semiconductor-metal ultraviolet photodetectors

Nanocrystalline TiO2 thin films were prepared by sol-gel method and were then used to fabricate metal-semiconductor-metal ultraviolet photodetectors with Au Schottky contact. It was found that dark current of the fabricated devices was only 1.9nA at 5V applied bias. High responsivity of 199A∕W was achieved when it was irradiated by the ultraviolet light (λ=260nm). The low dark current and high responsivity maybe attributed to the effect of Schottky barrier in company with neutral semiconductor owing to the wide finger gap of 20μm. The devices show a slow time response with a rise time of 6s and a decay time of 15s. The authors deduced that the slow time response was caused by defect traps which were widely distributed in nanocrysal.

Metal-semiconductor-metal TiO2 ultraviolet detectors with Ni electrodes

In this letter, metal-semiconductor-metal (MSM) TiO2 ultraviolet (UV) detectors with Ni electrodes have been fabricated. TiO2 thin films were prepared by sol-gel method. At 5 V bias, the dark current of the detector with Ni electrode was 1.83 nA. High photoresponse of 889.6 A/W was found under irradiation of 260 nm UV light, which was much higher than those of other wide bandgap UV detectors with MSM structure. The high photoresponse was due to the great internal gain caused by the hole trapping at interface. The rise time of the device was 13.34 ms and the fall time was 11.43 s.

Semitransparent inverted polymer solar cells with MoO3/Ag/MoO3 as transparent electrode

Semitransparent inverted polymer solar cells were developed using thermally evaporable MoO3/Ag/MoO3 as transparent anode. The ultrathin inner MoO3 layer was introduced as a buffer layer to improve hole collection, while the outer MoO3 layer served as a light coupling layer to enhance optical transmittance of the device. The dependence of the device performances on the thickness of the outer MoO3 layer was investigated. The results showed that the addition of the outer MoO3 layer improves the transmittance of the anode compared to MoO3/Ag anode and the performances of the semitransparent devices with the outer MoO3 layer are improved due to the reduced series resistance.

Performance improvement of TiO2∕P3HT solar cells using CuPc as a sensitizer

In this work, a new type of TiO2/polymer solar cells was fabricated. The device structure was indium tin oxide titanium dioxide (TiO2)/ copper phthalocyanine (CuPc)/poly(3-hexylthiophene) (P3HT)/Au. In this architecture, TiO2 was designed to act as electron acceptor, and P3HT was electron donor. CuPc was used as a sensitizer to enhance photon absorption. The results show that by inserting CuPc between P3HT and TiO2 layers, the light absorption, excitons separation, and photocurrent under illumination are dramatically improved. The device has a short current density (JSC) of 1.15mA∕cm2 and power conversion efficiency (η) of 0.28% without CuPc layer. However, JSC and η turn to be 2.22mA∕cm2 and 0.66%, respectively, with a 20nm thickness CuPc layer under air mass 1.5 global (AM1.5G) illumination with the intensity of 100mW∕cm2. The performance improvement can be attributed to the higher carrier mobility and the stronger photon absorption using CuPc as a sensitizing layer.

Semitransparent Polymer Solar Cells with 5% Power Conversion Efficiency Using Photonic Crystal Reflector

Efficient semitransparent polymer solar cells (ST-PSCs) have been fabricated with one-dimensional photonic crystals (1DPCs) as a high reflector. The 1DPCs are composed of several pairs of WO3 (65.8 nm)/LiF (95.5 nm). By optimizing the pairs of WO3/LiF, 1DPCs can reflect the light back into the ST-PSCs due to the photonic band gap, when the high reflectance range of 1DPCs is matched with absorption spectrum of the active layer. ST-PSCs with 8 pairs of 1DPC exhibit an attractive performance. The short-circuit current density (Jsc) and power conversion efficiency (PCE), respectively, reach to 9.76 mA/cm(2) and 5.16% compared to 8.12 mA/cm(2) and 4.24% of the reference ST-PSCs without 1DPCs. A maximum enhancement of 20.2% in Jsc is obtained and the PCE increases by ~21.7%. This approach provides a simple, fascinating and promising method to realize the highly efficient ST-PSCs toward applications.

Schottky Diode Ultraviolet Detector Based on

In this letter, a Schottky diode ultraviolet (UV) detector based on TiO2 nanowire (NW) array with Ag electrode is fabricated. The TiO2 NW array was prepared via a low-temperature hydrothermal method and characterized by means of X-ray diffraction, scanning electron microscope, and XPS. The Schottky barrier character of Ag/TiO2 contact was researched in detail. At -5-V bias, the dark current of the detector was less than 35 nA. Under the irradiation of 350-nm UV light, a high responsivity of 3.1 A/W was achieved due to the internal gain. The Schottky diode detector with simple fabrication process, low cost, and superior performance would provide a new way in fabricating UV imaging arrays.

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Window application is the important aim for semitransparent solar cells (STPSC) investigation. Here, we demonstrate a method to achieve significantly improved color rendering index (CRI), depressed chromaticity difference (DC), and enhanced power conversion efficiency (PCE) simultaneously by introducing the one-dimensional photonic crystals (1DPCs) Bragg reflector structure onto the STPSC. The device performance is studied from aspects of color perception, electrical properties, and theoretical optical simulations. The STPSCs exhibit achromatic transparency nature color perceptions, especially for the STPSCs with 1DPCs (pairs ≥ 3) under AM 1.5G illumination light source, standard illuminant D65, and standard illuminant A. The excellent CRI is approaching 97 with lower DC about 0.0013 for the device with 5 pairs of 1DPC illumined by AM 1.5G illumination light source. At the same time, the PCE of STPSC devices with 5 pairs of 1DPC was improved from 4.87 ± 0.14% to 5.31 ± 0.13% compared to without. This method provides a facilitative approach to realizing excellent SPTSC window application.

Nanowire Array

We demonstrate a novel solution-processed method to fabricate a stable anode buffer layer without any annealing process. As we know, buffer layers in polymer solar cells (PSCs) are always prepared by the traditional high-vacuum thermal evaporation or annealing-treated spin-coating methods, but the fabricating processes are complicated and time-consuming. Here, a solution method without any annealing to fabricate phosphomolybdic acid (PMA) as anode buffers is presented, which brings an obvious improvement of power conversion efficiency (PCE) from 1.75% to 6.57% by optimizing the PMA concentrations and interface pretreatment with device structure shown as ITO/TiO2/PCDTBT:PC70BM/PMA/Ag. The improvement is ascribed to the fine energy-level matching and perfect surface modification. This annealing-free method greatly simplifies the device fabrication process and supplies a wide way to achieve a large area fabrication for PSCs.