Photoluminescence ͑PL͒ and reflectivity spectra from modulation-doped CdTe/ Cd x Mg 1−x Te quantum well structures containing a two-dimensional electron gas have been studied in magnetic fields up to 45 T. In high fields, the recombination from the dark triplet trion state was found to be one of the most intense PL lines. A "bright" triplet line is revealed in both reflectivity and PL in magnetic fields above 35 T. PL spectra were calculated as a function of magnetic field, taking into account exciton, singlet, and triplet trion states. We show that the intense PL from the dark triplet trion is due to the field-induced suppression of singlet trion formation, and a corresponding enhancement of dark trion formation.
Herein, a comparison of industrial silicon heterojunction (SHJ) solar cells formed using p‐type (boron‐ or gallium‐doped) Czochralski‐grown silicon (Cz‐Si) wafers is provided. Standard n‐type SHJ solar cells are also fabricated as a reference. Boron‐doped SHJ solar cells are heavily susceptible to boron–oxygen light‐induced degradation (BO‐LID), with an open‐circuit voltage (VOC) reduction of 100 mV in some cells with starting VOC of >720 mV. While an advanced hydrogenation process (AHP) is sufficient to completely stabilize BO‐LID in some cells, resulting in stable VOC of 724 mV, the impact in reducing BO‐LID is variable. This suggests that an AHP alone may not be a reliable method of reducing BO‐LID in industrial SHJ solar cells. In contrast, SHJ solar cells formed using gallium‐doped wafers exhibit VOC > 730 mV and show no degradation during light‐soaking. Yet, the same AHP treatment for gallium‐doped SHJ cells results in a 0.4%abs increase in the conversion efficiency to 22.6% (VOC of 734 mV). The conversion efficiency of the gallium‐doped SHJ solar cells is still lower than the n‐type reference cells, which is largely due to a reduced fill factor (FF). Further work is required to overcome this FF limitation to facilitate high‐efficiency gallium‐doped SHJ solar cells.
Silicon heterojunction solar cells (HJSC) with the efficiency of about 20% are manufactured. Their short-circuit current, open-circuit voltage, photoconversion efficiency, and fill factor of the current–voltage curve are measured in a broad temperature range from 80 to 420 K. It is established that the open-circuit voltage, the fill factor, and the photoconversion efficiency are non-monotonic functions of temperature, having a maximum in the vicinity of 200 K. A new approach to modeling of HJSCs is proposed, which allows one to obtain quantitative agreement with the experimental results at temperatures above 200 K, as well as to describe the results published in the literature on the solar cells under AM1.5 conditions. The temperature coefficient of photoconversion efficiency in HJSCs is discussed, and its low value is shown to be related to the low surface and volume recombination rates. Finally, a theoretical expression for the SC's temperature under natural working conditions is derived.
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