Characterization of multiterminal tandem photovoltaic devices and their subcell coupling

Three-terminal (3T) and four-terminal (4T) tandem photovoltaic (PV) devices using various materials have been increasingly reported in the literature, but measurement standards are lacking. Here, multiterminal devices measured as functions of two load variables are characterized unambiguously as functions of three device voltages or currents on hexagonal plots. We demonstrate these measurement techniques using two GaInP/GaAs tandem solar cells, with a middle contact between the two subcells, as example 3T devices with both series-connected and reverse-connected subcells. Coupling mechanisms between the subcells are quantified within the context of a simple equivalent optoelectronic circuit. Electrical and optical coupling mechanisms are most clearly revealed using coupled dark measurements. These measurements are sensitive enough to observe very small luminescent coupling from the bottom subcell to the top subcell in the prototype 3T device. Quick simplified measurement techniques are also discussed within the context of the complete characterization. [Display omitted] Two types of 3T GaInP/GaAs tandems are fabricated and characterizedHexagonal plots unambiguously characterize multiterminal tandem solar cellsFive zero-power points of 3T tandems are analogous to the VOC and JSC of 2T devicesTiny luminescent coupling from the bottom to the top subcell of 3T tandem is quantified Three- and four-terminal tandem photovoltaic devices are becoming increasingly relevant. Geisz et al. demonstrate meaningful measurement techniques for unambiguously characterizing these devices using 3T GaInP/GaAs tandem solar cells as examples. Subcell coupling is sensitively quantified with coupled dark measurements that are fit to a simple equivalent optoelectronic circuit.