Origins of the short circuit current of a current mismatched multijunction photovoltaic cell considering subcell reverse breakdown

Abstract

In the photovoltaic community, short circuit current (Isc) of a current mismatched multijunction photovoltaic (MJPV) cell was usually thought to be limited by the lowest subcell photocurrent (Imin). However, under certain conditions for multijunction solar cells, Isc≠Imin was observed by researchers, while this effect has not been studied in multijunction laser power converters (MJLPCs). In this work, we provide an in-depth analysis of the formation mechanisms for the Isc of the MJPV cell by measuring I-V curves of the GaAs and InGaAs LPCs with different number of subcells and simulating the I-V curves with the reverse breakdown of each subcell considered. It is found that Isc of an N-junction PV cell can be theoretically equal to any current value within a range from a current lower than Imin to the maximum subcell photocurrent, which is up to the number of subcell current steps in the forward biased I-V curve. An MJPV cell with a constant Imin will demonstrate a higher Isc if it has more subcells, smaller subcell reverse breakdown voltage and smaller series resistance. As a result, Isc tends to be limited by the photocurrent of a subcell closer to the middle cell and is less sensitive to the optical wavelength than Imin. This should be another possible reason why the measured EQE of a multijunction LPC exhibits a wider spectrum width than the calculated Imin-based EQE, whereas this was usually attributed to the luminescent coupling effect merely.

Onset of Quantum-Confined Stark Effects in Multijunction Photovoltaic Laser Power Converters Designed with Thin Subcells

“…By biasing the multijunction device on a given plateau, the relative photocurrent of the corresponding subcell can be extracted at the probing wavelength. This method can be useful for extracting the responsivity, the quantum efficiency, the absorption coefficients, and the spectral response information for the heterostructure [18,31,32,40,41,44]. 1).…”

67.5% Efficient InP-Based Laser Power Converters at 1470 nm at 77 K

“…While research on laser power converter devices continues to progress in many groups [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37], our present study has expanded the possibilities for stable and reliable power-over-fiber or power-beaming devices that are obtained using vertical multijunction power converters. The multijunction design enables practical optimal loads and tailored output voltages.…”

Demonstration of Power-over-Fiber with Watts of Output Power Capabilities over Kilometers or at Cryogenic Temperatures

“…They have been productized for the 1450-1550 nm spectral range and also for cryogenic applications at ~1470 nm or ~808 nm [31][32][33][34]. Furthermore, the unrelenting developments in the field of photovoltaic devices further promise additional LPC device opportunities [35][36][37][38][39][40][41][42][43].…”