Artifact Interpretation of Spectral Response Measurements on Two‐Terminal Multijunction Solar Cells

Abstract

Multijunction solar cells promise higher power‐conversion efficiency than the single‐junction. With respect to two‐terminal devices, an accurate measurement of the spectral response requires a delicate adjustment of the light‐ and voltage‐biasing; otherwise it can result in artifacts in the data and thus misinterpretation of the cell properties. In this paper, the formation of measurement artifacts is analyzed by modeling the measurement process, that is, how the current–voltage characteristics of the component subcells evolve with the photoresponse to the incident spectrum. This enables the examination on the operation conditions of the subcells, offering additional information for the study of artifacts. In particular, the influence of shunt resistance, bias‐light intensity, and bias voltage on the measurement is examined. Having observed the dynamics and vulnerability of the measurement, the proper ways to configure and interpret a measurement are discussed in depth. As a practical example, simulations of the measurements on a quadruple‐junction thin‐film silicon solar cell demonstrate that the modeling can be used to interpret eventual irregularities in the measured spectral response. The application of such tool is especially meaningful taking account of the diverse and rapid development of novel hybrid multijunction solar cells, in which the role of reliable characterizations is essential.

Quadruple‐Junction Thin‐Film Silicon Solar Cells Using Four Different Absorber Materials

“…A bias voltage was applied to offset the subcell being measured to its short‐circuit condition. The measurement principle is further described in literature …”

Organic tandem solar cells: How impedance analyses can improve the quality of external quantum efficiency measurements

“…For a specific tandem solar cell, V bias is inherently linked to the selective bias light spectrum and intensity . The spectrum of the bias light affects, depending on the EQE of the subcells, the required bias illumination intensity.…”

Measurement of the limiting subcell in multijunction space solar devices by restricted‐wavelength‐range illumination

“…1,2 When monolithic architectures are considered, in 2 (tandem), 3, and several junctions configurations, the phenomenon of current limitation is a fundamental factor to consider during device planning. 1,[3][4][5] Such an effect requires to establish ab initio which subcell will be the limiting one in order to suitably tailor the current behavior.…”

“…Although it is a widely used characterization method, the presence of several possible artifacts requires a rather delicate data processing. 5,18,22,23 A further class of measurement techniques exploits light sources with a specifically tailored spectrum: This causes the selectively illuminated solar device to provide a greater response from one subcell with respect to the others. [24][25][26][27] We here employ this same principle for developing a specific method to determine the limiting subcell in irradiated multijunction monolithic solar cells for space applications.…”