Function Analysis of the Phosphine Gas Flow for n-Type Nanocrystalline Silicon Oxide Layer in Silicon Heterojunction Solar Cells

The energy conversion efficiency (eta) of silicon heterojunction (SHJ) solar cells is limited by the current losses in the layer stack on the illuminated side. To reduce these losses, hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) was implemented as a window layer in SHJ solar cells. However, the integration of nc-SiOx:H in devices without degradation of fill factor (FF) is still a challenge. To optimize the electron performance of devices, the optoelectronic properties and microstructure of nc-SiOx:H were characterized and analyzed systematically. It was found that the PH3 gas fraction (f(PH3)) plays a big role on the microstructure, oxygen content, and phosphorus (P) doping efficiency of the films. The highest conductivity, 2.84 x 10(-1) S/cm, is obtained at a moderate f(PH3) with an optical band gap of 2.26 eV. A ternary model was creatively used to show the variation in the composition of nc-SiOx:H as tuning f(PH3). The growth of crystalline phase was accelerated by the P dopants when f(PH3) is low, but further increasing f(PH3) leads to excessive P inactive dopants, causing a phase transition from nanocrystalline silicon to amorphous silicon in nc-SiOx:H. In this work, the best solar cell with an ncSiO(x):H window layer achieves an FF of 81.4%, a short current density (J(sc)) of 39.8 mA/cm(2), an open-circuit voltage (V-oc) of 731 mV, and an eta of 23.7% at the moderate f(PH3). A decrease in FF and J(sc) is shown with higher f(PH3), which is the consequence of the increased front contact resistivity and decreased optical band gap of nc-SiOx:H window layer.

Automated summary

The study focuses on optimizing the performance of solar cells by using hydrogenated nanocrystalline silicon oxide as a window layer in silicon heterojunction solar cells, emphasizing the significant influence of PH3 gas fraction on film properties. The best solar cell performance is achieved at a moderate PH3 gas fraction with high conductivity and efficiency.