The properties of n‐GaP/p‐Si interface as well as their influence on solar cell performance are studied for GaP layers grown by low‐temperature (380 °C) plasma‐enhanced atomic layer deposition (PE‐ALD). The influence of different plasma treatments and RF power values are explored. The increase of RF power leads to a growth transition from amorphous (a‐GaP) to microcrystalline GaP (μc‐GaP) with either amorphous‐GaP/Si or epitaxial‐GaP/Si interface, respectively. However, when continuous hydrogen plasma is used the amorphous‐GaP/Si interface exhibits better photovoltaic performance compared to the epitaxial one. Values of open circuit voltage, Voc = 0.45–0.55 V and internal quantum efficiencies, IQE > 0.9 are obtained for amorphous‐GaP/Si interfaces compared to Voc = 0.25–0.35 V and IQE < 0.45 for epitaxial‐GaP/Si interfaces. According to admittance spectroscopy and TEM studies the near‐surface (30–50 nm) area of the Si substrate is damaged during growth with high RF power of hydrogen plasma. A hole trap at the level of EV + (0.33 ± 0.02) eV is detected by admittance spectroscopy in this damaged Si area. The damage of Si is not observed by TEM when the deposition of the structures with epitaxial‐GaP/Si interface is realized by a modified process without hydrogen plasma indicating that the damage of the near‐surface area of Si is related to hydrogen plasma interaction.
International audienceThe temperature dependence of the capacitance of very high efficiency silicon heterojunction solar cells exhibits an anomalously large increase with temperature that cannot be explained under the usual depletion approximation. Based on a full calculation of the capacitance, we show that this large increase of capacitance with temperature of p-type hydrogenated amorphous silicon (a-Si:H)/n-type crystalline silicon (c-Si) heterojunctions occurs when a strong inversion layer at the c-Si surface appears. It is further shown that due to the promotion of inversion as the temperature increases, the temperature at which strong inversion appears depends on the valence band offset and position of the Fermi level in a-Si:H. Therefore, a simple analysis of the temperature dependence of silicon heterojunction solar cells' capacitance can be used to reveal the presence of a strong inversion, to study details of the band diagram and to get insight into the heterointerface
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