Voltage reduction in a non-uniformly illuminated solar cell

Abstract

A simple mathematical expression is derived for the reduction in the voltage at the output terminals of a solar cell due to non-uniform illumination of the junction plane. The voltage from a solar cell non-uniformly illuminated by light is always less than that from a similar cell uniformly illuminated by light and generating the same amount of short-circuit current. For a small change in the voltage, an approximate expression predicts a constant shift in the I-V characteristics of a solar cell, towards the lower voltage side.

A monolithic three‐terminal GaInAsP/GaInAs tandem solar cell

“…The open-circuit voltage rises logarithmically with concentration with slopes of 1.07 and 0.86kT/q for the top and bottom cells, respectively, where q is the elementary charge. We believe that the bottom cell slope is reduced below 1kT/q as a consequence of the 28% shadowing from the busbars and contacts, which tends to reduce the voltage 13 ; the ideality factor measured from the dark IV was only slightly greater than unity as expected for a high quality GaInAs cell. Indeed following the analysis in Reference [13] and using the IV parameters found here, we predict the dependence to be V oc $ 0.92kT/qÁLn(J sc /J 0 ) because of the shadowing, which is in good agreement with the data given the assumptions behind the model in Reference [13].…”

“…We believe that the bottom cell slope is reduced below 1kT/q as a consequence of the 28% shadowing from the busbars and contacts, which tends to reduce the voltage 13 ; the ideality factor measured from the dark IV was only slightly greater than unity as expected for a high quality GaInAs cell. Indeed following the analysis in Reference [13] and using the IV parameters found here, we predict the dependence to be V oc $ 0.92kT/qÁLn(J sc /J 0 ) because of the shadowing, which is in good agreement with the data given the assumptions behind the model in Reference [13]. While Auger recombination is also a mechanism that yields an ideality factor less than unity, at a relatively lowdoping level of $10 17 cm À2 we do not expect Auger recombination to be significant.…”

“…2 V oc for both cells could improve slightly if the shadowing were minimized, 13 either by extending the lateral size of the cell or by shrinking the busbars and contacts to suit wirebonds rather than laboratory probes. As we have described, the J sc of the top cell is excellent; J sc for the bottom cell is also good, achieving about 83% of the modeled photocurrent for that cell, but with the bottom cell producing only 20% of the total power, the bottom cell J sc only accounts for about half of the drop in performance.…”

Characterizing thermophotovoltaic cells

“…Nonuniform light incident on a cell and nonuniform thermal contact of the cell to a temperature-controlled plate will cause a temperature gradient to exist. This temperature gradient will reduce the fill factor and voltage at a given current, compared with the uniformly illuminated case [14]. These effects can be minimized by using a pulsed light source.…”

Desarrollo de células solares de doble unión de GaInP/GaAs para concentraciones luminosas elevadas (Development of GaInP/GaAs dual-junction solar cells for high light concentrations).

“…In [Dhariwal81] the reduction of V oc with non-uniform light profiles was explained as the consequence of the lateral current flows generated by the potential gradient caused by the non-uniform carrier generation. By using a solar cell in which a region was illuminated and the rest of the area was left in the dark, a mathematical expression for the voltage negative increment produced in a solar cell with a non-uniform light profile was derived.…”