Spectral response and I-V characteristics of large well number multi quantum well solar cells

Abstract

The inclusion of quantum wells in p-i-n solar cells leads to both an increase in photocurrent and a reduction in open circuit voltage. It has been shown that up to 50 shallow strain-balanced GaAsP/InGaAs quantum wells can be inserted into a GaAs cell resulting in an increase in photocurrent that is greater than the reduction in V_oc, leading to higher cell efficiency [1]. We present an investigation into the effects of a further increase in well number. The spectral response and IV characteristics of a 65 well quantum well solar cell and an otherwise identical 50 well cell are presented and compared. In addition, the ideality n = 1 dark currents obtained from these samples at concentrator current levels are studied. The predicted and measured light current densities under forward bias are compared at one sun illumination and demonstrate additivity to a good approximation. The results obtained suggest that cell efficiency decreases as well number increases from 50 to 65. Additionally, a 65 well cell of reduced exciton wavelength is also considered and found to demonstrate additivity at AM1.5 g short-circuit current levels and projected efficiency equal to that of the 50 well cell.