Meng-Yueh Liu

High Efficiency Flexible Polymer Solar Cells Based on PET Substrates with a Nonannealing Active Layer

The inverted bulk-heterojunction solar cell on the polyester (PET) substrate with a nonannealing active layer is investigated. The atomic force microscope images show that the morphology of the nonannealing active layer of the inverted plastic solar cell evolves with time, which improves the performance of the solar cell. Our investigations show that the grain size of the active layer increases with time, resulting in improvements in the fill factor (from 34.8 to 62.8%) and shunt resistance (from 107 to 505 Ω cm 2 ) as well as a reduction in the series resistance (from 4.82 to 0.96 Ω cm 2 ). The easily processed inverted device with a nonannealing active layer on the indium tin oxide-coated PET substrate exhibits a high power conversion efficiency of ~ 3.66%.

Accurate measurement of performance of polymer solar cell with highly conductive PEDOT:PSS

Correlation between the power conversion efficiency and dimethyl sulfoxide (DMSO) modified poly (3,4-ethylene dioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) of polymer solar cells is studied. The PEDOT:PSS is modified by adding process additive (DMSO) during processing. However, highly conductive DMSO-PEDOT:PSS leads to tremendous errors in the measurement of the polymer solar cells. Our investigations show that the light illumination area of the polymer solar cells based on the DMSO-PEDOT:PSS has to be further adjusted before measurement.

Solution-processed vanadium oxide interlayer for improving the performance of polymer/ZnO nanorod hybrid solar cells

A solution-processed vanadium oxide interlayer is introduced between the organic layer and the electrode for improving the performance of the polymer/ZnO nanorod hybrid solar cells. The results indicate that the vanadium oxide interlayer can serve as an electron-blocking layer to suppress the leakage current and an optical spacer to increase light absorption. As a result, the power conversion efficiency is improved from 2.52% to 3.56%, with a fill factor of 60% under 100 mW/cm2 irradiation.

Effect of solvent on morphological properties of TiOx thin film

Sol-gel preparation of amorphous titanium oxide (TiOx) thin films with distinct morphological properties on the hydrophobic substrate was obtained by solution spin coating method. The TiOx thin films were deposited by three precursors using 2-methoxyethanol (2MOE), isopropanol (IPA) and mixture of 2MOE and hexane as solvents. We demonstrate evidence that the morphology of TiOx thin film is strongly related to the employment of dissimilar solvent. Among these three solvents, TiOx film obtained from 2MOE/hexane mixed solvent is a superior choice for the preparation of TiOx thin film on the hydrophobic substrate because of its smooth surface morphology.

Improved performance of polymer/ZnO nanorod hybrid solar cells by slow drying of the photoactive layer

The slow drying of the photoactive layer in polymer/ZnO nanorod hybrid solar cells is studied as a way to improve device performance. The power conversion efficiency can be further improved to 3.05% with an enhanced fill factor of 55% by slowing the spin coating rate of photoactive layer. With the slower spin coating rate, the films of photoactive layer are thicker, and the polymer chains have longer time to self-organize and more effectively infiltrate into ZnO nanorod spacing, resulting in the higher crystallinity of polymer and light harvesting without sacrificing the carrier transportation.

Performance enhancement of organic/inorganic hybrid solar cells by improving the optical absorption of polymer

The performance of the polymer/ZnO nanorod hybrid solar cells based on poly(3-hexylthiophene) and methanofullerenes is improved with the enhanced optical absorption by increasing the thickness of the photoactive layer and introducing a solution-processed interlayer. The dependence of the optical absorption on the thickness of the photoactive layer is studied as a function of the spin-coating rate. With the slower spin-coating rate, the photoactive layer is thicker, and the polymer chains have longer time to self-organize and more effectively infiltrate into ZnO nanorod spacing. In addition, a solution-processed fullerene interlayer is introduced to modify the ZnO nanorod surface. With this interlayer, the optical absorption of the photoactive layer increases due to the better ordering of the photoactive layer. Our investigations show that the power conversion efficiency (PCE) is improved from 1.6% to 2.6% with the thickness of the photoactive layer from 240 nm to 350 nm by slowing the spin coating rate of the photoactive layer. Moreover, the PCE is also improved by the fullerene interlayer. The slow-drying method and the solution-processed fullerene interlayer both improve the crystallinity of the polymer and light harvesting.

High efficiency of flexible polymer solar cell based on poly(3- hexylthiophene)/fullerene

The inverted bulk hetero-junction solar cell on the polyester (PET) substrate with a non-annealing active layer is investigated. Our investigations show that the easily processed inverted device with a non-annealing active layer on the indium-tin-oxide coated PET substrate exhibits a high power conversion efficiency of ∼3.65%.

Solution-processed fullerene interlayer for organic-inorganic hybrid solar cells

Organic-inorganic hybrid solar cells as low-cost renewable energy sources have attracted great attention due to the possibility of fabricating them on large-area, light-weight, flexible substrates by printing and coating technologies. Hashimoto et al. investigated the performance dependence of poly(3-hexylthiophene) (P3HT): (6,6)-phenyl C61 butyric acid methyl ester (PCBM)/ZnO hybrid solar cells on the length of the ZnO nanorods and reported a PCE up to 2.7 % [1]. However, compared to the polymer solar cells, the hybrid solar cells tend to have lower PCEs due to poor electrical coherence at the organic/inorganic interface. One approach to solve this issue is to modify the organic/inorganic interface with a functional interlayer. However, few studies focus on solution-processed interlayer for hybrid solar cells with ZnO nanorod arrays. In this work, we introduce a solution-processed fullerene interlayer at the P3HT:PCBM/ZnO interface to improve the photovoltaic performance. Compared to vacuum process for most interlayer [2, 3], the solution process offers the advantage of low cost.

Air-stable polymer/ZnO nanorod hybrid solar cell

During the past years, there have been numerous interests in the fabrication of polymer solar cells due to its flexibility and easy fabrication process. The most common system so far for polymer solar cells is the one consisting of poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl C61 butyric acid methyl ester (PCBM) that is sandwiched between poly(3,4-ethylene dioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) and Al metal. However, conventional bulk-heterojunction (BHJ) architecture has limitations in device stability. Without encapsulation, exposure of conventional solar cells to air leads to oxidation of the Al electrode and degradation of the indium tin oxide (ITO)/ PEDOT:PSS interface because of the acidic nature of PEDOT:PSS[1]. One approach to improve device stability is using polymer/ZnO nanorod hybrid solar cell. In our solar cell, the interface of ITO/PEDOT:PSS can be avoided by employing ZnO nanorod using a hydrothermal method and the low-work-function metal Al can be replaced by Ag. ZnO nanorod is used as an excellent electron selective layer and Ag has the nature of less air sensitivity.