Photoconversion devices

We can specify the conditions for the above sequences of reactions to be possible in terms of thermodynamic quantities provided we can ascribe these to electronically excited states. This is normally possible for excited states in bulk condensed phases because these become thermalised , i.e. vibrationally and rotationally equilibrated with their enviromnent, extremely rapidly (usually within a few picoseconds), long before they undergo any chemical reaction. It is however not possible to assume thermalisation in space-quantised stractures such as quantum dots, in which relatively long-lived hot carriers are generated by photoexcitation. Indeed, the very slowness of thermalisation in space-quantised stractrrres makes it possible to envisage photoconversion devices in which hot carriers can deliver more work than wotrld be thermodynamically possible with thermalised carriers. Nozik discusses such possibihties in Chapter 3. 

In several cases of interest in photoconversion devices, the species D or A to be oxidised or reduced at the electrode is not in close contact with the electrode surface, but deliberately separated from it by a short distance. The separator may be, for example, a thin passivating film, a molecular spacer layer or an electron-transporting bridge B in an electrode-B-A or electrode-B-D assembly such as a self-assembled monolayer (SAM). 

As this chapter should have demonstrated, a detailed understanding of the mechanism of ET reactions has now been achieved by the efforts of many theoreticians and experimentalists, and we shall conclude it by reflecting on the lessons for photoconversion devices based on photoinduced electron transfer reactions. 

Fig. 7.21 CurrentAoltage response curves of photoconversion devices with good and poor fill factors (FF), showing maximum voltage, current, and power points for each curve...

PHCs were soon considered for photoconversion devices. The use of electro-deposited thin films of PP has been proposed for preventing photocorrosion of... 

Single crystal silicon (sc-Si), polyciystalline silicon (p-Si), and amorphous silicon (a-Si) can all be used to make solar cells, with fabrication cost and device photoconversion efficiencies decreasing as one moves from single-crystal to amorphous materials. Various properties of these materials are summarized in Table 8.1. Other relatively common solar cell materials include gallium arsenide (GaAs), copper indiirm diselenide (CIS), copper indium-gallium... 

Several device concepts employing conjugated polymers as active components in the photoconversion process of photovoltaic devices have been presented to date. With power conversion efficiencies surpassing 5% (polymer-fullerene), reaching 3% (hybrid polymer-nanoparticle), or 2% (polymer-polymer), the prospects are high. 

This section focuses on charge transfer in synthetic polymer solid phases (for metal enzymes refer to Chapter 2). In many electronic devices such as electrocatalytic systems, sensors, and electrochromic display or photoconversion systems, charge transfer between redox molecules... 

However, physical methods suffer from microscopic-level phase separation [155] between the two constituents. This occurs due to the removal of solvent molecules which not only cause the aggregation of nanocrystals to form super-crystals but also lead to partial crystallization of regioregular polymeric chains. In such type of hybrids, it is difficult to realize the intimacy between QCNs and CP at nanometer scale. The loose networks of QCNs scatter the electrons in electronic devices which in turn leads to poor device efficiency, e.g., in solar cells, it is responsible for low photoconversion efficiency due to deterioration of the efficiency at charge generation, separation, and transport steps. In order to overcome above limitations, efforts have been made to improve the intimacy between the phases by adopting chemical methods that involve means for realizing chemical linking between two partners. 

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