Solar temperature behavior

Temperature Behavior of Bulk Heterojunction Solar Cells... 

The influence of the preparation temperature on the devices characteristics was investigated on both types A and B samples prepared at the optimum [CuPc] [C6o] = l ldonor-to-acceptor ratio. The solar cells efficiency (Fig. lb) is mainly dominated by the temperature behavior of Jsc and FF (not shown). For both types of samples a maximum efficiency is achieved at Tsubstrate 150°C. However, the B-type samples with the optimized contacts show by up to 3 times higher efficiencies compared to A-type devices. At the optimum substrate temperature the best B-type OSC shows the following PV parameters ... 

One might ask Why does not the atmosphere always have an adiabatic lapse rate as its actual profile The reason it does not is that other processes such as winds and solar heating of the Earth s surface lead to dynamic temperature behavior in the lowest layers of the atmosphere that is seldom adiabatic. These other processes exert a much stronger influence on the prevailing temperature profile than does the adiabatic rising and failing of air parcels. 

A cosmochemical periodic table, illustrating the behavior of elements in chondritic meteorites. Cosmic abundances are indicated by symbol sizes. Volatilities of elements reflect the temperatures at which 50°/o of each element would condense into a solid phase from a gas of solar composition. As in Figure 1.2, the chemical affinities of each element, lithophile for silicates and oxides, siderophile for metals, and chalcophile for sulfides, are indicated. Some of the most highly volatile phases may have remained uncondensed in the nebula. Stable, radioactive, and radiogenic isotopes used in cosmochemistry are indicated by bold outlines, as in Figure 1.2. Abundances and 50% condensation temperatures are from tabulations by Lodders and Fegley (1998). 

Additional outdoor measurements of Voc made while continuously varying the cell temperature, without recording the entire I/V curve, confirm this behavior (Fig. 5.49). For all samples, the observed linear decrease has a temperature coefficient in the range dVoc/dT ss 1.40-1.65 mV/K. This is comparable with corresponding values observed for familiar inorganic solar... 

In order to try and understand the physical mechanisms which may be responsible for the observed temperature dependence of Voc in the high and low temperature ranges, it is instructive to start with an analysis of the Voc behavior of conventional inorganic semiconductor solar cells with a p-n junction [150] ... 

In the previous section on the short-circuit current, it was demonstrated theoretically and experimentally that Isc in conjugated polymer-fullerene solar cells is controlled to a considerable extent by mobility of the majority charge carriers in the cell s active layer [158]. Moreover, activated behavior of charge carrier mobility in conjugated polymers is known to result in higher mobility at higher temperatures (for a review, see [159]). Accordingly,... 

A similar temperature dependence of Isc, Voc, and r) is also reported for the lower mobility generation of solar cells, based on interpenetrating networks of conjugated polymers with fullerenes, but processed from solvents so that the initial efficiency is < 1% [156]. This behavior is discussed extensively in the section dealing with Isc. A positive temperature coefficient is also observed for the efficiency of Cgo single-crystal photoelectrochemical cells [160]. Finally, a temperature dependence of Isc qualitatively similar to that shown in Fig. 5.47a and 5.48 is also observed for organic solar cells based on Zn-phthalocyanine (ZnPc)/perylene (MPP) heterojunctions [161]. 

Furthermore, these data strongly suggest that the positive temperature dependence of Isc, FF, and r) may be characteristic for solar cells based on organic semiconductors that show a temperature-activated behavior for charge transport, resulting in higher mobility/conductivity at higher temperatures (as also observed, for example, for some types of amorphous silicon solar cells [162]). 

The poly-Si films obtained by ALILE process always show p-type behavior. On high temperature resistant foreign substrates, the p-type poly-Si can be transferred to n-type poly-Si by overdoping, e.g., by phosphorous diffusion at 950°C [68], This allows for other solar cell configurations (e.g., substrate/ n+-type ALILE seed layer/n-type absorber/p+-type emitter). 

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