Biasing photovoltaics

Microwave biased Photovoltaic effect p — M junction Avalanche p — i — n... 

Fortunately, such a microscope can now be fitted with a multi-element detector to measure multiple areas simultaneously. One multi-element detector approach is to construct quasi-lD arrays from the same Hgi xCdxTe photo-conductive material as for a single-element detector, providing essentially the same spectral range and performance. Each element can be individually biased and read-out by an AC coupled amplifier having bandwidth compatible with FT-IR scanner velocities of 1 cm/s or above. Larger area, 2D arrays are usually made with photovoltaic elements i.e. photodiodes) to avoid the current biasing... 

Photovoltaic cells were prepared with a polymer layer sandwiched between electrodes with different work functions, as in polymer-based LEDs (Fig. 29.2). In the dark, the device exhibits a rectification ratio of 10 at 3.5 V. Under illumination, devices of this type show a strong photoresponse, with open-circuit voltages of 0.6 V and short-circuit currents that correspond to quantum efficiencies of up to 6%. Under forward or reverse biases, the quantum efficiencies rise rapidly, reaching 15% at a reverse bias of 3.5 V, 40% at 10 V. and considerably higher values under forward bias. These performance figures are very much better than those for devices made with aluminum electrodes and either MEH-PPV or CN-PPV alone. Thus, Halls et al. report values for the quantum yield of the short-circuit photocurrent in the MEH-PPV of 0.04% at the peak response wavelength (2.2 eV) and on the order of 10 %... 

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