Dopant-Free Hydrogenated Amorphous Silicon Thin-Film Solar Cells Using Molybdenum Oxide and Lithium Fluoride

Toxic doping gases are usually used to produce hydrogenated amorphous silicon (a-Si:H) layers in thin-film solar cells (TFSCs). Hence, an alternative structure that avoids the use of toxic gases is desirable. In this work, we replaced both the p-type-a-Si:H and n-type-a-Si:H layers simultaneously in a normal TFSC to form a structure that is dopant-free. Molybdenum oxide (MoO3) and lithium fluoride were used as the p-type and n-type layers, respectively. The effects of the deposition method and the thickness of the MoO3 layer on the device performance were investigated. The power-conversion efficiency of the optimized hybrid solar cell reached a maximum of 7.08%, which is remarkable considering the novel structure of the dopant-free devices. The light stability of the devices with and without MoO3 was also compared: the light stability of the device with MoO3 was found to be much better than that of the device without MoO3 and with p-i-n Si layers. This was ascribed to the insignificant number of defect sites generated by the nondoping elements, which led to a less contaminated, more compact, and smoother oxide surface, resulting in an increase in the electron lifetime and improved light stability. This work opens up a new direction toward the development of a truly dopant-free device that does not involve the use of toxic gases during fabrication and provides the potential for further enhancement of the efficiency of future dopant-free solar cells.