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Silicon solar cells mainly absorb visible light, although the sun emits ultraviolet (UV), visible, and infrared light. Because the surface reflectance of a textured surface with SiNX film on a silicon solar cell in the UV wavelength region (250-450 nm) is higher than ∼27%, silicon solar-cells cannot effectively convert UV light into photo-voltaic power. We implemented the concept of energy-down-shift using CdSe/ZnS core/shell quantum-dots (QDs) on p-type silicon solar-cells to absorb more UV light. CdSe/ZnS core/shell QDs demonstrated clear evidence of energy-down-shift, which absorbed UV light and emitted green-light photoluminescence signals at a wavelength of 542 nm. The implementation of 0.2 wt% (8.8 nm QDs layer) green-light emitting CdSe/ZnS core/shell QDs reduced the surface reflectance of the textured surface with SiNX film on a silicon solar-cell from 27% to 15% and enhanced the external quantum efficiency (EQE) of silicon solar-cells to around 30% in the UV wavelength region, thereby enhancing the power conversion efficiency (PCE) for p-type silicon solar-cells by 5.5%.

We developed a conductive-bridging random-access memory cell with a sandwiched structure of an Ag top electrode, an electrolyte (polyethylene oxide: PEO), and a Pt bottom electrode on a 250-nm hole pattern. The cell demonstrated the bipolar switching behavior of resistive randomaccess memory. The nonvolatile characteristics of the cell strongly depended on the wt% (PEO thickness): i.e., maximum memory characteristics, such as a retention-time of > 1 × 105 s with a memory margin of 1 × 104 and program/erase cycles of > 103 with a memory margin of 1.3 × 104, which are very close to thereof a commercial memory cell, were observed at a specific wt% of PEO (0.4 wt%)

We investigated the dependence of nonvolatile memory characteristics on curing temperature for a polymer nonvolatile 4F 2 memory-cell embedded with Au nanocrystals in poly(N-vinylcarbazole) (PVK). The curing temperature is an important factor for determining the size, shape, and isolation presence of Au nanocrystals embedded in the PVK layer. When the curing temperature rises above 300 °C, ∼8-nm spherical Au nanocrystals are uniformly distributed and well isolated. Thus, the nonvolatile memory-cell demonstrated a memory margin of ( I on / I off ) of 9.8 × 10 1 , retention time of 1 × 10 5 s and more than 100 program/erase endurance cycles.

In summary, we successfully developed the polymer nonvolatile 4F2 memory-cell. It was based on nonvolatile memory characteristics such as memory margin and retention time, which was observed in memory-cell embedded with Ag nanocrystals in PVK layer. The nonvolatile memory characteristics depend on the shape, distribution and isolation of Ag nanocrystals. Accordingly, the thickness of Ag film has an important role in optimizing the Ag nanocrystals. Therefore, the polymer nonvolatile memory-cell is fabricated by appropriate thickness of film and need an improvement of interface between Ag nanocrystals and PVK for sufficient nonvolatile memory characteristics.

We have been researching the polymer nonvolatile memory-cell based on electrical bi-stability. The polymer nonvolatile memory-cell was the 4F2 embedded with Ag nano-crystals in conductive polymer. The structure of polymer nonvolatile memory-cell was PVK(poly(N-vinylcarbazole) / Ag nano-crystals / PVK between the Al electrodes. The Ag nano-crystals were formed by using the curing process after evaporate several nanometers of Ag layer. The polymer nonvolatile memory-cell embedded with Ag nano-crystals showed the memory magin(ratio of I on to I off ) is ∼5.0×101. The retention time is more than 105 seconds.

Many researchers have investigated organic nonvolatile memory devices as one of candidates device for next generation nonvolatile memory because of their low-cost, flexible and simple fabrication. The memory phenomenon in these devices is based on the electrical bistability of the material, which has two resistance states. We report memory effect in organic molecules based on electrical bistability of the materials and the bistable phenomenon was observed in poly(N-vinylcarbazole) (PVK) layer, containing a high density of Au nanocrystals and sandwiched between Al electrodes. The device was fabricated on cleaned SiO2. First, Al for the bottom electrode was deposited on SiO2 substrate by thermal evaporation in a vacuum chamber (pressure ∼10−6 torr). The PVK was dissolved with chloroform, spin-coated on the Al electrode, and baked at 120¡ÆC for 2 min to evaporate the solvent away. Subsequently, a 5-nm-thick Au film was deposited on the PVK. Additional PVK was then spin-coated on the Au film and baked. Next, the device was cured at 300¡É for 2 h in air to produce the Au nano-crystals. This device showed good nonvolatile memory characteristics. It was confirmed that it shows several region of current levels, (ION, IOFF, IINTER). When the voltage increased from zero in the OFF state (low conductivity state), the current increased rapidly at the threshold voltage (Vth), and presented a regime of negative differential resistance (NDR) after writing. Moreover ON and OFF states could be set at voltages at Vprogram (or Vp) and Verase (or Ve), respectively, and could be read at 1 V. After the device was programmed by sweeping the voltage from 0 to Vp, the current followed the high conductivity state and stayed in the ON state. And the device was programmed by sweeping the voltage from 0 to Ve, the current followed the low conductivity state and stayed in the OFF state. Furthermore, they exhibited seven different reversible current paths (intermediate states) capable for approving electron charge or discharge on surface of Au nanocrystals by sweeping the voltage from 0 to VNDR. Our results demonstrate that the fundamental parameters of the device were stable; the values of Vth, Vp, and Ve were ∼2.8, ∼4, and ∼8 V, respectively. In particular, this device exhibited excellent nonvolatile memory behavior, with bistability (ION/IOFF) of >1×102 and an intermediate state for multi-bit operation. We suggest that the current conduction mechanism clearly follow space-charge-limited(SCLC) for low conductivity state, thermionic field emission for electron charge(writing) or discharge(erasing), and F-N tunneling after erasing.

Recently, non-volatile polymer memories have been researched as a next generation of non-volatile memory because of its simple structure and easy fabrication process. We found that two types of non-volatile polymer memory have different I-V behavior. First Polymer non-volatile memory with metal / oxide / polymer / metal structure But Polymer non-volatile memory embedded Au Nano-crystal shows different I-V behavior. Polymer non-volatile memory shows NDR(Negative Differential Resistance) Region after threshold voltage and low to high current path at increasing positive and negative bias. We can observe NDR(Negative Differential Resistance) Region on Polymer non-volatile memory embedded Au Nano crystal. We fabricated devices three different type to confirm difference Polymer non-volatile memory with metal / polymer / metal structure, metal / oxide / polymer / metal structure and Au nano-crystal embedded Polymer non-volatile memory. First we fabricated Polymer non-volatile memory with metal / PVK(Poly-n-vinyl carbarzole) / metal structure. first type of device shows ohmic I-V behavior. Second type of polymer non-volatile memory has oxide layer between metal and polymer layer. Oxide layer made by O2 plasma treatment(100W RF power, 100SCCM O2 gas flow) after metal layer deposited. Second type of device has same structure as first device except oxide layer. Second type of device shows I-V behavior similar to Resistive Memory. Resistive non-volatile memory shows low to high current path at increasing positive bias and high to low current path at increasing negative bias. I-V behaviors of second device due to effect of oxide layer between metal and polymer layer. Third type of polymer non-volatile memory we embed Au nano-crystal layer in polymer layer. Au nano-crystal layer embedded by curing process. We deposit 5nm Au layer after spin coated PVK(Poly-n-vinyl carbarzole) layer and curing at 300¡É. We can observe NDR(Negative Differential Resistance) Region and different I-V behaviors with other type of device. Finally we fabricated polymer non-volatile memory embedded au nano-crystal by dispersion method to confirm effect of au nano-crystal. We report difference I-V behaviors polymer non-volatile memory with metal / polymer / metal structure and polymer non-volatile memory embedded au nano-crystals

Flexible conductive-bridging random-access-memory (RAM) cells were fabricated with a cross-bar memory cell stacked with a top Ag electrode, conductive polymer (poly(n-vinylcarbazole): PVK), electrolyte (polyethylene oxide: PEO), bottom Pt electrode, and flexible substrate (polyethersulfone: PES), exhibiting the bipolar switching behavior of resistive random access memory (ReRAM). The cell also exhibited bending-fatigue-free nonvolatile memory characteristics: i.e., a set voltage of 1.0 V, a reset voltage of -1.6 V, retention time of1 × 10(5) s with a memory margin of 9.2 × 10(5), program/erase endurance cycles of10(2) with a memory margin of 8.4 × 10(5), and bending-fatigue-free cycles of ∼1 × 10(3) with a memory margin (I(on)/I(off)) of 3.3 × 10(5).

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