Reciprocal relationship between photoluminescence and photocurrent in two-step photon up-conversion solar cell
Noriyuki Kinugawa, Shigeo Asahi, Takashi Kita
Kobe University, Kobe, Japan

 Two-step photon up-conversion solar cell (TPU-SC) we have recently proposed is a single-junction solar cell containing a hetero-interface comprising a wide gap semiconductor (WGS) and a narrow gap semiconductor (NGS). Low-energy photons generate carriers in the NGS. The excited electrons are obstructed at the hetero-interface because of the potential barrier of the conduction band offset of the hetero-interface. Since these electrons are already separated from holes, long-lived electron densely accumulate at the hetero-interface, enabling efficient two-step photon up-conversion (TPU).  Although efficient TPU has been achieved in the TPU-SC, the detailed mechanism of intraband photoexcitation occurring at the hetero-interface is still unclear. In this study, we investigated the physics of the TPU occurring at the hetero-interface and performed simultaneous measurement of photocurrent (PC) and photoluminescence (PL) of InAs quantum dots which is inserted beneath the hetero-interface while applying bias voltage. The PC increased while the PL peak-intensity decreased with an increase in a reverse-bias voltage. In addition, the application of the additional infrared light caused a decrease in the PL-peak intensity together with an increase in the PC. Besides, the summation of the radiative recombination current, which is evaluated by the PL-peak intensity, and the PC exhibited almost constant in the range of reverse-bias voltage, suggesting that the reciprocal relationship between the PL and the PC satisfies in the TPU-SC. Furthermore, the PL peak-intensity strongly depends on the bias voltage, while the change in the PL-peak intensity by the additional infrared light exhibited almost constant in the range of reverse bias. This presumes that the electron density in the fundamental-states of the InAs quantum dots is constant and that the hole density is strongly affected by the electric field.