En- Chen

Micro-textured conductive polymer/silicon heterojunction photovoltaic devices with high efficiency

In this work, hybrid heterojunction solar cells are demonstrated based on a conjugate polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) directly spun-cast on micro-textured n-type crystalline silicon wafers. The fabrication conditions suggest that the organic coverage on the micro-textured surface is excellent and key to achieve high efficiency, leading to an average power conversion efficiency of 9.84%. A one-dimensional drift-diffusion model is then developed based on fitting the device characteristics with experimentally determined PEDOT:PSS parameters and projects an ultimate efficiency above 20% for organic/inorganic hybrid photovoltaics. The simulation results reveal the impacts of defect densities, back surface recombination, doping concentration, and band alignment.

Continuous blade coating for multi-layer large-area organic light-emitting diode and solar cell

A continuous roll-to-roll compatible blade-coating method for multi-layers of general organic semiconductors is developed. Dissolution of the underlying film during coating is prevented by simultaneously applying heating from the bottom and gentle hot wind from the top. The solvent is immediately expelled and reflow inhibited. This method succeeds for polymers and small molecules. Uniformity is within 10% for 5 cm by 5 cm area with a mean value of tens of nanometers for both organic light-emitting diode (OLED) and solar cell structure with little material waste. For phosphorescent OLED 25 cd/A is achieved for green, 15 cd/A for orange, and 8 cd/A for blue. For fluorescent OLED 4.3 cd/A is achieved for blue, 9 cd/A for orange, and 6.9 cd/A for white. For OLED with 2 cm by 3 cm active area, the luminance variation is within 10%. Power conversion efficiency of 4.1% is achieved for polymer solar cell, similar to spin coating using the same materials. Very-low-cost and high-throughput fabrication of efficient ...

Increasing organic vertical carrier mobility for the application of high speed bilayered organic photodetector

The direct influence of the vertical carrier mobility on the frequency response of bilayered organic photodiodes (PDs) is investigated for the first time. With fullerene as the acceptor material, changing vertical hole mobility from 2.3×10−5 to 2.8×10−4 cm2/V s increases PD bandwidth from 10 to 80 MHz under a 4 V operation. The influence of deposition rate on vertical hole mobility of pentacene film is also discussed. Our results facilitate the application of bilayered organic PDs on the detection of very-high-frequency optical signals.

Polymer photodetector with voltage-adjustable photocurrent spectrum

Polymer photodetectors with voltage-adjustable photoresponse from visible to near infrared range are demonstrated. Poly(3-hexylthiophene) and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) blend is used as the active layer. The photoresponse can be continuously adjusted by the thickness of the active layer as well as the applied voltage bias. The thickness of the active layer is varied from 250 nm to 16.2 μm. The mechanism for the photoresponse adjusted by the thickness can be attributed to the absorption of the photons in the infrared range by thick PCBM layer. The mechanism for the photoresponse adjusted by the applied bias can be attributed to the carrier recombination reduction when the applied bias increases. The adjustable photodetector also has high operating speed up to 10 kHz.

Polymer infrared proximity sensor

A proximity sensor that combines a polymer light-emitting diode and a polymer photodiode is presented. The operation wavelength is in the near infrared from 700to850nm. The infrared emission is obtained by adding a color conversion film of polyvinylpyrrolidone polymer matrix blended with infrared dye 1,1-diethyl-2,2-dicarbocyanine iodide to a red polymer light-emitting diode. The photodetector relies on the direct charge-transfer exciton generation in a donor-acceptor polymer blend of poly(3-hexylthiophene) and (6,6)-phenyl-C61-butyric acid methyl ester. The detection distance is up to 19cm for objects with various colors and roughness under ambient indoor lighting.

Polymer Infrared Proximity Sensor Array

A near-infrared proximity sensor array is achieved by integrating a polymer light-emitting diode and a polymer photodetector (PD). A green emission is converted into deep red peaked at 670 nm by the inorganic phosphor Intematix R670 with quantum efficiency of over 20%. A bandpass filter is used to select a spectral tail of phosphor luminescence with a wavelength above 700 nm. The emissive polymer is green polyfluorene. The infrared PD contains a thick film of a blend of poly(3-hexylthiophene) and (6,6)-phenyl-C61-butyric acid methyl ester up to a thickness of 8 m. Position of a moving object at a distance of 10 cm is detected in real time by the array with dynamic images displayed on the computer screen.

Multilayer rapid-drying blade coating for organic solar cells by low boiling point solvents

A bulk heterojunction organic solar cell with poly(3-hexylthiophene) (P3HT) as the donor and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor is deposited using blade coating on a hot plate at 80 °C with hot air of 70 °C applied from above. In contrast to the 30 min of conventional dichlorobenzene solvent annealing, the rapid-drying blade coating forms a dry film in 1 s. The fabrication throughput is substantially enhanced. The blade-coated film has a smoother surface roughness of 3.5 nm compared with 10.5 nm for solvent annealing; however, the desired phase separation in the 50 nm scale forms despite the rapid drying. A single layer solar cell exhibits power conversion efficiency of 4.1% with blade coating in chlorobenzene, which is the same as solvent annealing device. A multilayer device with carrier blocking layers fabricated entirely of the less toxic toluene also exhibits efficiency of 4.1%.

Fabrication and device modeling of micro-textured conductive polymer/silicon heterojunction solar cells

In this paper, hybrid heterojunction solar cells are demonstrated based on a highly conductive polymer PEDOT:PSS directly spun-cast on an n-type crystalline silicon with microscale surface textures. The fabrication conditions suggest that the organic coverage on the micro-textured surface is excellent and key to achieve high efficiency. The simple solution-based fabrication processes achieved a cell power conversion efficiency of 10.2%. Device modeling had been performed to investigate the interface defect density dependence of cell performances. A power conversion efficiency of above 20% is projected for the hybrid heterojunction cells, showing promises for low-cost photovoltaics.

Solution-processed silicon hybrid heterojunction photovoltaics with silver nanowires

An Organic/inorganic hybrid solar cells are cheap alternatives to conventional silicon-based solar cells. The devices take the advantages of high optical absorption and carrier mobility of inorganic semiconductors, while maintaining the easy processing attributes of polymers or other soft materials. However, the conduction of holes has been a major technical barrier for the advance of such novel devices. In this study, we propose the use of silver nanowires (AgNWs) to improve the series resistance of the hybrid solar cells and further to realize solution-processed silicon-based photovoltaics. The hybrid silicon heterojunction solar cells are demonstrated based on the composite of conductive polymer PEDOT:PSS directly spun-cast on a micro-textured n-type crystalline silicon wafer, followed by the Meyer rod coating of AgNWs as the frontal metal contacts. The cross linked AgNWs offer high transparency and low sheet resistance, which can be easily fabricated using low-cost and non-toxic materials. Moreover, the industrial-standard microscale surface textures improve the antireflection and carrier collection without increasing much surface recombination. As a result, the device current density-voltage characteristics reveals a high power conversion efficiency of 6.8% under a calibrated illumination intensity of 1000 W/m2 of the AM1.5G solar spectrum, shedding light into the attainment of rapid solution processed silicon hybrid heterojunction solar cells.