Polymer spectral response

Comparison of the spectral response and of the power efficiency of these first conjugated polymer/fullerene bilayer devices with single layer pure conjugated polymer devices showed that the large potential of the photoinduced charge transfer of a donor-acceptor system was not fully exploited in the bilayers. The devices still suffer from antibatic behavior as well as from a low power conversion efficiency. However, the diode behavior, i.e. the rectification of these devices, was excellent. 

Figure 15-24. Spectral response or devices nude wilh different PEOPT polymer thicknesses Al/C ) (35 nm)/PEOPT (30 nin)/PEDOT-PSS (110 unU/lTO (120 ninj/glass (solid circles) and AI/Cm (35 nm)/PEOPT (40 iini)/Pl DOT-PS.S (110 mn)/lTO (120 ninj/glass (open circles). The absorption spectrum of the PEOPT polymer is plollcd for comparison (solid line) (reproduced by permission of Wiley-VCH from Ref. (92]).

However, for relatively new types of solar cells such as the polymer-based solar cells described here, suitable stable reference cells cannot yet be fabricated. This implies that, for measurements concerning these cells, calibrated reference cells are used (Si, GaAs) with a different spectral response to the device under test, resulting in mismatch factors that deviate significantly from 1. It is therefore of the utmost importance to carry out the procedure as precisely as possible in order to minimise measurement errors. 

The research presented here pursues the question of the electronic spectra of PDA crystals by employing both of these approaches. In the first, the spectra of a series of PDAs with differing urethane sidechains (Table I) are investigated. Variance of the number of sidechain methylenes is expected to affect the distance between the polymer spines in the lattice thereby altering the spectral response. 

Zaban A., Koren E., Lubomirsky I. and Cahen D. (2006), Extending the spectral response of dye-sensitized, organic, and polymer solar cells , unpublished work. 

The spectral response of two devices with different thin PEOPT layers is shown in Figure 15-24. The IPCE for the 30 nm PEOPT device is as high as 23% at the maximum and still 17% for the thicker device. Also of importance is the similarity between the action spectrum and the absorption spectrum of the conjugated polymer. Both curves are very similar with the absorption spectrum slightly red-shifted. The energy conversion efficiency of the most optimized device was calculated to be 1.7% at low light intensities (15 pW/cm ) under monochromatic illumination. 

Many other systems based on different nanoparticles have been introduced, such as copper indium disulfide (CuInS2) [263-265], copper indium diselenide (CuInSe2) [266,267], cadmium telluride (CdTe) [268], lead sulfide (PbS) [269,270], lead selenide (PdSe) [271], and mercury telluride (HgTe) [272]. Some of these systems show enhanced spectral response well into the infrared part of the solar spectrum [271,272]. In most cases the absorption of the nanocrystals was, however, quantitatively small as compared to the conjugated polymers. 

All these phenomena can occur simultaneously within the same material, as illustrated by the spectral response of an oriented polymer doped with DCM dye (4-dicyanomethylene-2-methyl-6-p-dimethylamino-styryl-4H-pyran) under 1.06 iJ,m laser irradiation (Figure 1.1). The two sharp signals at 532 and 354 nm are coherent emission induced by SHG and THG, whereas the broad band is incoherent emission of two-photon excited fluorescence (TPEF). 

Fig. 5.15. Spectral response of a ring-mode structure consisting of a 25-mm diameter silica fiber dip-coated with a polymer 1 thin film. ASE attenuation in the absence of spontaneous emission attenuation occurs after 1.5 min exposure to saturated TNT vapor pressure. (inset) Plots of ASE peak emission intensity (A = 535 nm) as a function of excitation power. TNT exposure increases the pump energy threshold...

Studies indicate that PFSeBT is a potential polymer functioning as an electron donor in polymer photovoltaic cells [203,204]. The devices have a spectral response up to 680 nm. An open-circuit voltage of 1.00 V and a short-circuit current density of 4.42 mA cm are achieved. The energy conversion efficiency is 1.67%. 

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