Abstract
We studied the effect of deposition temperature on the hydrogen distribution and the passivation performance of hydrogenated amorphous silicon (a-Si:H) coated crystalline silicon (c-Si) heterojunctions as a model of high efficiency solar cell structures. Nuclear reaction analysis (NRA) was employed to obtain hydrogen depth profiles of the heterojunctions prepared at temperatures from 80 to 180 °C. The implied open circuit voltage (i-VOC) and carrier lifetime monotonically increased with increasing deposition temperature in the as-deposited samples. NRA clarified that the hydrogen concentration (CH) at the a-Si:H/c-Si interface and in the a-Si:H layer decreased with deposition temperature. The hydrogen concentration around the interface was roughly 3 × 1021 cm-3 for the sample deposited at 180 °C. The NRA results are supplemented by optical constants obtained with spectroscopic ellipsometry (SE). At higher growth temperature, larger refractive indices and extinction coefficients were confirmed by SE analysis, suggesting that fewer hydrogen atoms are incorporated into the a-Si:H layers prepared at higher growth temperature. Furthermore, the passivation performance was enhanced by post deposition annealing (PDA) at 200 °C for 30 min. No significant change of the hydrogen distribution and optical constants was observed after PDA, suggesting that improved passivation is due to a local rearrangement of hydrogen at the molecular level that results in enhanced hydrogenation of dangling bonds.
Highlights
We studied the effect of deposition temperature on the hydrogen distribution and the passivation performance of hydrogenated amorphous silicon (a-Si:H) coated crystalline silicon (c-Si) heterojunctions as a model of high efficiency solar cell structures
Decreased τeff and i-VOC values were observed for the intrinsic type a-Si:H (i-a-Si):H/n-type c-Si(100) (n-c-Si) heterojunctions fabricated at Tdepo = 205 ○C
It is reported that the deterioration of the passivation performance at high Tdepo is caused by crystallization of the a-Si:H layer and crystallization is promoted by post deposition annealing (PDA).11,16,17
Summary
Silicon heterojunction (SHJ) solar cells employing hydrogenated amorphous silicon (a-Si:H) have garnered significant attention owing to their extremely high conversion efficiency. The high conversion efficiency is primarily due to the passivation of the crystalline silicon (c-Si) surface by intrinsic type a-Si:H (i-a-Si:H), which suppresses carrier recombination at the c-Si surface and allows for a high open circuit voltage (VOC). Korte et al proposed that two recombination pathways of photogenerated carriers exist in a-Si:H passivated c-Si: recombination of carriers via dangling bonds at the a-Si:H/c-Si heterointerface and in the bulk of a-Si:H.4 According to the description of the surface recombination mechanism, the interface recombination rate depends on the interface state density, which is proportional to the density of interfacial dangling bonds. A low density of interfacial dangling bonds is believed to arise from hydrogenation of Si dangling bonds. The hydrogenation of dangling bonds around a-Si:H/c-Si heterointerfaces is regarded as the origin of the passivation effect, there are few reports on the correlation between passivation performance and hydrogen distribution around a-Si:H/c-Si heterointerfaces. Silicon heterojunction (SHJ) solar cells employing hydrogenated amorphous silicon (a-Si:H) have garnered significant attention owing to their extremely high conversion efficiency.. The high conversion efficiency is primarily due to the passivation of the crystalline silicon (c-Si) surface by intrinsic type a-Si:H (i-a-Si:H), which suppresses carrier recombination at the c-Si surface and allows for a high open circuit voltage (VOC).. Korte et al proposed that two recombination pathways of photogenerated carriers exist in a-Si:H passivated c-Si: recombination of carriers via dangling bonds at the a-Si:H/c-Si heterointerface and in the bulk of a-Si:H.4. According to the description of the surface recombination mechanism, the interface recombination rate depends on the interface state density, which is proportional to the density of interfacial dangling bonds.. The quantitative investigation of the hydrogen distribution near the scitation.org/journal/adv a-Si:H/c-Si interface is necessary for a fundamental comprehension of the passivation mechanism by a-Si:H and for further device optimization
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