Shang-Chieh Chien

Increased open circuit voltage in fluorinated benzothiadiazole-based alternating conjugated polymers

Small band-gap conjugated polymers based on monofluoro- and difluoro-substituted benzothiadiazole were developed. Highly efficient polymer solar cells (PCE as high as 5.40%) could be achieved for devices made from these polymers.

Facile synthesis of a 56π-electron 1,2-dihydromethano-[60]PCBM and its application for thermally stable polymer solar cells

A facile synthesis was employed to make a 56π-electron methano-PC(61)BM with a very small 1,2-dihydromethano (CH(2)) group. This new fullerene derivative possesses high electron mobility (0.014 cm(2) V(-1) s(-1)) and higher LUMO energy level (0.15 eV) than PC(61)BM. Bulk hetero-junction devices based on using poly(3-hexylthiophene) and methano-PC(61)BM as active layer exhibited better performance and thermal stability than those using the PC(61)BM analogue.

Nanoscale functional interlayers formed through spontaneous vertical phase separation in polymer photovoltaic devices

A nanoscale interlayer formed through spontaneous vertical phase separation enhances the efficiency and stability of polymer solar cells. Poly(ethylene glycol) molecules blended into the photoactive layer spontaneously migrate to the surface of the polymer blend to form the interfacial buffer, thereby reducing the contact resistance after undergoing chemical reactions with the Al atoms of the cathode. The vertical phase separation of PEG molecules in the device were investigated by using depth profiling scanning electron microscopy and atomic force microscopy.

Highly sensitive, low-voltage, organic photomultiple photodetectors exhibiting broadband response

Highly sensitive polymer photodetectors exhibiting broad spectral responses, ranging from the ultraviolet to the near-infrared (NIR) region, are obtained after incorporating an organic NIR dye into the device active layer. As a result, high external quantum efficiencies (>7000%) and high responsivities (32.4 A/W) are achieved at an extremely low operating voltage (−1.5 V). The high photomultiplation could be attribute to trapping of electrons, originating from the photogenerated electron/hole pairs, at the dye molecules, which effectively facilitates hole injection from the external circuit. The device preparation scheme presented herein opens up the possibility fabricating lost-cost, flexible organic photodetectors.

Single-layer triplet white polymer light-emitting diodes incorporating polymer oxides: Effect of charge trapping at phosphorescent dopants

This paper describes the effects of charge trapping on the device performances of triplet polymer light-emitting diodes (PLEDs) after the cathode contact had been improved through the blending of poly(ethylene glycol) (PEG) into the active layer. The external quantum efficiency (EQE) was enhanced when the dopant tended to trap electrons. In contrast, we observed no EQE enhancement for the device featuring a hole-trapping dopant. Because PEG promoted electron injection, more electrons were trapped in the triplet molecules, thereby enhancing the probability of recombination. Finally, after incorporating PEG, we further achieved white PLEDs exhibiting both high EQE and high power efficiency.

Extended spectral response in organic photomultiple photodetectors using multiple near-infrared dopants

We demonstrate highly sensitive polymer photodetectors (OPDs) with spectral response extending from the ultraviolet to the near-infrared (NIR) region (∼1200 nm). After doping two NIR dopants, high external quantum efficiencies (∼5500%) and high responsivities (23.0 A/W) are achieved under a low reverse bias (−3.7 V). The high gains could be attributed to unbalanced carrier transport in the photoactive layer arising from the electron traps at the NIR dopants. This approach allows the ready preparation of OPDs exhibiting broad spectral responses and high quantum efficiencies simultaneously.

Flexible polymer solar cells prepared using hard stamps for the direct transfer printing of polymer blends with self-organized interfaces

A transfer printing technique allows the development of flexible photovoltaic devices. Blending poly(ethylene glycol) (PEG) in the photoactive layer causes the PEG molecules to migrate spontaneously to and weaken the bonding at the interface between the polymer film and the Si wafer, thereby facilitating the transfer process from a hard stamp to the receiving flexible substrate. The device fabricated using this transfer printing process had characteristics similar to those of the corresponding device prepared using a spin-coating process. Using hard stamps should help to realize the low-cost, high-throughput roll-to-roll fabrication of flexible solar cells.

High-Performance Single-Layer Polymer Electrophosphorescent Devices with Polymer Oxides

An enhanced power efficiency and a lower driving voltage of polymer electrophosphorescent devices have been demonstrated by blending poly(ethylene glycol) (PEG) into the active layer. The luminance efficiency of the device with Al cathode was up to 15.6 cd/A and the turn-on voltage was decreased to 5.6 V after the use of PEG. Further, the power efficiency was also improved to 5.0 Im/W. Moreover, similar improvement was also observed while Ca/Al or LiF/Ca/Al were used as the cathodes. The performance enhancement can be attributed to the interaction between Al and organic molecules with ethylene oxide groups, resulting in a better contact.

P‐223: Enhanced Power Efficiency of Single‐Layer White Triplet Polymer Light‐Emitting Diodes by Blending with Polymer Oxides

In this study, we have demonstrated enhanced performance of blue, red and white phosphorescent polymer light-emitting diodes PLEDs) by blending poly(ethylene glycol) (PEG) into the active layer of the devices. By introducing PEG into the PLEDs, the turn-on voltages of these devices became lower than those of the conventional devices. In addition, the luminance efficiency and the external quantum efficiency of the blue and white phosphorescent PLEDs were both improved. Most important of all, because of the lower operating voltage, the higher power efficiency (7.3 lm/W, 1.5 lm/W, 4.6lm/W) of the blue, red and white phosphorescent PLEDs than those of the control devices (2.9 lm/W, 1.1 lm/W, 1.9 lm/W) have been achieved, respectively. Finally, the improvement mechanism will be discussed.

Surface Plasmonic Effects of Nanostructures on the Performance of Polymer Solar Cells

In this chapter, we review recent progress related to the incorporation of plasmonic nanostructures in organic photovoltaic devices (OPVs) as a means of enhancing power conversion efficiencies. We begin by describing the fundamental properties of surface plasmons (SPs) . We then outline the two primary schemes that are commonly employed for excitation of the SPs: the use of noble metal particles to trigger the SPs and the creation of propagating surface plasmon polaritons (SPP) through approaches that can overcome the problem of momentum mismatch (e.g., periodic corrugation at the metal–dielectric interface). Next, we discuss some recent remarkable approaches toward increasing the light absorption efficiency of OPVs, highlighting three categories of plasmonic structures that enhance the performance of OPVs. Finally, we provide a brief outlook regarding the future use of SPs in high-efficiency OPVs.