研究目的
Investigating the detailed mechanism of intraband photoexcitation occurring at the hetero-interface of a two-step photon up-conversion solar cell (TPU-SC) and demonstrating the reciprocity relationship between the radiative recombination and the photocurrent of the TPU-SC.
研究成果
The study demonstrates a reciprocal relationship between photoluminescence and photocurrent in the TPU-SC, with the summation of radiative recombination current and PC being almost constant in the range of reverse-bias voltage. The electron density in the fundamental-states of InAs QDs is constant below 0.6 V, while the hole density is strongly affected by the electric field, revealing the physics of TPU occurring at the hetero-interface.
研究不足
The study focuses on the TPU-SC with a specific hetero-interface configuration (Al0.7Ga0.3As / GaAs) and InAs QDs, which may limit the generalizability of the findings to other materials or configurations. The efficiency of additional photocurrent generation due to the TPU is noted to be too low to achieve the theoretically predicted high conversion efficiency in actual device operation.
1：Experimental Design and Method Selection:
The study involved simultaneous measurements of photoluminescence (PL) and photocurrent (PC) as a function of the applying bias voltage in the TPU-SC to elucidate the electron accumulation at the hetero-interface and its effect on the efficiency of TPU.
2：Sample Selection and Data Sources:
A TPU-SC was fabricated on a p+-GaAs (001) substrate using solid-source molecular beam epitaxy, containing an Al
3：7Ga3As / GaAs hetero-interface with an InAs quantum dots (QDs) layer inserted beneath the hetero-interface. List of Experimental Equipment and Materials:
A continuous-wave laser diode with a wavelength of 784 nm for the first excitation light, a supercontinuum white laser for the second excitation infrared (IR) light, a 1300 nm long-pass filter, Keithley SourceMeter for applying bias voltage and measuring PC, a single monochromator for spectral dispersion of PL, and an InGaAs diode-array detector for PL detection.
4：Experimental Procedures and Operational Workflow:
The first excitation light penetrates Al
5：7Ga3As and excites GaAs, while the second IR light excites electrons accumulated at the hetero-interface. PC and PL were measured simultaneously while applying the bias voltage. Data Analysis Methods:
The relationship between PC and PL was analyzed under the condition that the power density of the first excitation light is constant, leading to the evaluation of the proportional coefficient k between PL intensity and radiative recombination current.
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