AM0 concentration operation of III-V compounds solar cells

III-V compounds solar cells were examined by concentrated illumination of AM0 sunlight. High concentration or nonuniform illumination was found to bring significance degradation of FF due to apparent degradation of a diode ideality factor or “rounded” I-V curve. The output current at the maximum power point dropped as a result. This paper covers an experimental evaluation, analysis and solutions to that problem. It was found that a distributed diode model explained a behavior of the I-V curve under high concentration or nonuniform concentration operation. The output current drop was responsible from modulation of surface voltage of the emitter. Raised voltage at inter-grid region ignited parasitic diodes and had it leak a part of the output current. For the purpose of quantified analysis and solutions, the distributed diode model was expanded. Behaviors of I-V curve or FF were described by simple arithmetic functions with two basic new parameters, a nondimensional finger pitch and a normalized resistance, which were independent to the type of solar cells, accompanied with the combination of cell-dependent basic parameters, such as V_oc or I_sc. The impact to FF degradation could be summarized into counter plots. Basic design parameters such as finger pitch and series resistance could be designed with avoiding FF degradation by high concentration illumination. It was found that reduction of series resistance was not very important for multi-junction space concentrator cells. The key was reduction of nondimensional finger pitch and maintenance of uniform surface voltage