Device efficiency

However, not all excitons have sufficiently long lifetimes to reach the interface before recombining. To circumvent this problem and increase device efficiency, heterostmcture devices have been fabricated. In these devices, donors and acceptors are mixed together to create a network that provides many internal interfaces where charge separation can occur. Heterostmcture devices made from the donor polymer... 

Amorphous Silicon. Amorphous alloys made of thin films of hydrogenated siUcon (a-Si H) are an alternative to crystalline siUcon devices. Amorphous siUcon ahoy devices have demonstrated smah-area laboratory device efficiencies above 13%, but a-Si H materials exhibit an inherent dynamic effect cahed the Staebler-Wronski effect in which electron—hole recombination, via photogeneration or junction currents, creates electricahy active defects that reduce the light-to-electricity efficiency of a-Si H devices. Quasi-steady-state efficiencies are typicahy reached outdoors after a few weeks of exposure as photoinduced defect generation is balanced by thermally activated defect annihilation. Commercial single-junction devices have initial efficiencies of ca 7.5%, photoinduced losses of ca 20 rel %, and stabilized efficiencies of ca 6%. These stabilized efficiencies are approximately half those of commercial crystalline shicon PV modules. In the future, initial module efficiencies up to 12.5% and photoinduced losses of ca 10 rel % are projected, suggesting stabilized module aperture-area efficiencies above 11%. 

Other electron-deficient heterocyclic systems have also been investigated as electron-transporting materials. In particular, devices employing poly(phenyl qui-noxaline) 43 as an ECHB layer have shown improvements in device efficiency when used in conjunction with an emissive PPV layer [75]. 

The precise control of ROMP methodology has been exploited by Schrock and co-workers in the polymerization of a norbomene monomer functionalized with a distyrylbenzene side-chain 70 [1051. When calcium is used as a cathode, an internal device efficiency of 0.3% is observed and the peak emission is in the blue (475 nm). 

The electrodeposited precursor films prepared in our laboratory that produced high-efficiency devices were Cu-rich films. These precursor films required additional In, Ga, and Se, deposited by PVD, to adjust their final composition to Culni xGaxSe2. During this second step, the substrate temperature was maintained at 560 °C 10 °C. Figure 7.7 presents the Auger analysis of the final absorber and shows nonuniform distribution of Ga in the absorber and more Ga near the surface. This result is primarily from the second-stage PVD addition. The Ga hump is not helpful for hole collection. The device efficiencies are expected to increase by optimizing the Ga distribution in the absorber layers. The optimized layers should have less Ga in the front and more Ga on the back, which facilitates hole collection. 

J-S Kim, PKH Ho, NC Greenham, and RH Friend, Electroluminescence emission pattern of organic light-emitting diodes implications for device efficiency calculations, J. Appl. Phys., 88 1073-1081, 2000. 

It was shown that adding low oxidation potential material to PFs can stabilize the emission color and increase the device efficiency [321]. However, using low-molecular-weight organic dopants causes several problems such as phase separation and crystallization. These problems can be partially solved by using polymer blends. Cimrova and Vyprachticky [334] reported... 

Nevertheless, the device efficiency correlates with the above-mentioned charge transfer processes the dopant Btp2Ir with the lowest triplet energy showed the highest EQE (2%). 

Clearly, using a triplet emitter with shorter excited state lifetime should improve the device efficiency. In 2002, Cao and coworkers [65] used iridium complexes Ir(ppy)3 (3) and its... 

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