Plasmonic ITO-free polymer solar cell

Numerical Analysis of Optical Absorption Effect in Nonhalogen Solution-Processed, Inverted Small Molecule Solar Cell

Inverted solution-processed SMPV1:PC71BM small molecule organic photovoltaic solar cells (SM-OPVs) were fabricated. The power conversion efficiency (PCE) of halogen-free SM-OPVs reached around 5.07%. The absorption spectra at different device thicknesses were simulated by software Fluxim SETFOS 5.0, and compared with the experimental results. To further enhance the performance of halogen-free SM-OPVs, the interface between the active layer and the electrode of the optimized device was treated with the solvent vapor annealing (SVA) process, improving the PCE of the inverted halogen-free SM-OPV to 7.21%.

Well-aligned Vertically Oriented ZnO Nanorod Arrays and their Application in Inverted Small Molecule Solar Cells

This manuscript describes how to design and fabricate efficient inverted solar cells, which are based on a two-dimensional conjugated small molecule (SMPV1) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), by utilizing ZnO nanorods (NRs) grown on a high quality Al-doped ZnO (AZO) seed layer. The inverted SMPV1:PC71BM solar cells with ZnO NRs that grew on both a sputtered and sol-gel processed AZO seed layer are fabricated. Compared with the AZO thin film prepared by the sol-gel method, the sputtered AZO thin film exhibits better crystallization and lower surface roughness, according to X-ray diffraction (XRD) and atomic force microscope (AFM) measurements. The orientation of the ZnO NRs grown on a sputtered AZO seed layer shows better vertical alignment, which is beneficial for the deposition of the subsequent active layer, forming better surface morphologies. Generally, the surface morphology of the active layer mainly dominates the fill factor (FF) of the devices. Consequently, the well-aligned ZnO NRs can be used to improve the carrier collection of the active layer and to increase the FF of the solar cells. Moreover, as an anti-reflection structure, it can also be utilized to enhance the light harvesting of the absorption layer, with the power conversion efficiency (PCE) of solar cells reaching 6.01%, higher than the sol-gel based solar cells with an efficiency of 4.74%.

Design and development of plasmonic nanostructured electrodes for ITO-free organic photovoltaic cells on rigid and highly flexible substrates

Indium tin oxide (ITO) is the most common transparent electrode used in organic photovoltaics (OPVs), yet limited indium reserves and poor mechanical properties make it non-ideal for large-scale OPV production. To replace ITO, we designed, fabricated, and deployed plasmonic nanostructured electrodes in inverted OPV devices. We found that active layer absorption is significantly impacted by ZnO thickness which affects the optical field distribution inside the resonant cavity formed between the plasmonic nanostructured electrode and top electrode. High quality Cr/Au nanostructured electrodes were fabricated by nanoimprint lithography and deployed in ITO-free inverted devices on glass. Devices with thinner ZnO showed a PCE as high as 5.70% and higher J _SC's than devices on thicker ZnO, in agreement with finite-difference time-domain simulations. In addition, as the active layer was made optically thin, ITO-based devices showed diminished J _SC while the resonant cavity effect from plasmonic nanostructured electrodes retained J _SC. Preliminary ITO-free, flexible devices on PET showed a PCE of 1.82% and those fabricated on ultrathin and conformable Parylene substrates yielded an initial PCE over 1%. The plasmonic electrodes and device designs in this work show promise for developing highly functioning conformable devices that can be applied to numerous needs for lightweight, ubiquitous power generation.

Enhance the light-harvesting capability of the ITO-free inverted small molecule solar cell by ZnO nanorods

The ITO-free inverted SMPV1:PC₇₁BM solar cells with an Al doped ZnO (AZO) transparent electrodes are fabricated. The AZO thin film prepared by pulsed laser deposition (PLD) technique exhibits high transmission (>85%) and low sheet resistance (~30 Ω/sq) and the power conversion efficiency (PCE) of devices based on AZO electrode can reach around 4%. To further enhance the light harvesting of the absorption layer of solar cells, ZnO nanorods interlayer is grown on the AZO layer before the deposition the active layer. The absorption spectrums of devices under various conditions are also simulated by RCWA method to identify the optical saturation length of the ZnO nanorods. The PCE of ITO-free inverted small molecule solar cell improved with ZnO nanorods can reach 6.6%.

Photon harvesting, coloring and polarizing in photovoltaic cell integrated color filters: efficient energy routing strategies for power-saving displays

We describe the integral electro-optical strategies that combine the functionalities of photovoltaic (PV) electricity generation and color filtering as well as polarizing to realize more efficient energy routing in display technology. Unlike the conventional pigment-based filters and polarizers, which absorb substantial amounts of unwanted spectral components and dissipate them in the form of heat, we propose converting the energy of those photons into electricity by constructing PV cell-integrated color filters based on a selectively transmitting aluminum (Al) rear electrode perforated with nanoholes (NHs). Combining with a dielectric-metal-dielectric (DMD) front electrode, the devices were optimized to enable efficient cavity-enhanced photon recycling in the PV functional layers. We perform a comprehensive theoretical and numerical analysis to explore the extraordinary optical transmission (EOT) through the Al NHs and identify basic design rules for achieving structural coloring or polarizing in our PV color filters. We show that the addition of thin photoactive polymer layers on the symmetrically configured Al NH electrode narrows the bandwidth of the EOT-assisted high-pass light filtering due to the strongly damped anti-symmetric coupling of the surface modes excited on the front and rear surface of the Al NHs, which facilitates the whole visible coloring with relatively high purity for the devices. By engineering the cut-off characteristics of the plasmonic waveguide mode supported by the circular or ellipsoidal Al NHs, beyond the photon recycling capacity, PV color filters and PV polarizing color filters that allow polarization-insensitive and strong polarization-anisotropic color filtering were demonstrated. The findings presented here may shed some light on expanding the utilization of PV electricity generation across new-generation energy-saving electrical display devices.

Design and fabrication of birefringent nano-grating structure for circularly polarized light emission

Three different nano-grating structures are designed as phase retarders that can transform linearly polarized light to circularly polarized emission for the wavelengths of 488 nm, 532 nm and 632.8 nm, respectively. Gold based nano-grating structures with various periods are fabricated by utilizing laser interference lithography. The ellipticity of all circularly polarized emission can reach around 90% such that the structure has great potential in the applications of three-dimensional (3D) display. The effects of the slit width and metal thickness modulations are simulated by rigorous coupled wave analysis (RCWA) method. Besides, the field intensity and phase of the transmitted TM and TE waves are also simulated to understand their polarization characteristics.