The advantages of employing i-a-SiO_X:H as a buffer layer in hydrogenated amorphous silicon oxide solar cells

Abstract This study focuses on a p-i-n single junction solar cell made of hydrogenated amorphous silicon oxide (a-SiOx:H), aiming to enhance solar cell efficiency by mitigating the impact of discontinuities and mismatches occurring at the i/p defect-rich interface between the window layer and the absorber layer. To address this concern, the impact of adding a thin i-a-SiOx:H buffer layer between the p-a-SiOx:H window layer and the i-a-SiOx:H active layer was investigated through numerical modeling using the AMPS-1D (Analysis of Micro-electronic and Photonic Structures) computer program. Implementing these changes led to a remarkable increase in conversion efficiency, rising from 5.714% to an impressive 8.929%. The increase in short-circuit current (J SC ), however, is due to improved quantum efficiency at short wavelengths between 350 and 550 nm. Furthermore, enhancing the built-in potential (Vbi) at the i/p interface, combined with the buffer layer’s appropriate band gap energy, increases V OC (open-circuit voltage) from 850 to 993 mV. The substantial improvement in the fill factor (FF) from 63.1 to 83.1% can be largely attributed to the smoothed band offset, primarily facilitated by the presence of the buffer layer at the p/i interface, which led to more efficient extraction of photogenerated holes. To ensure effective usage of the buffer layer, the thickness of a-SiOx:H (buffer layer) varied between 3 nm and 9 nm, while the p-type doping concentration of the same layer was adjusted between 0 and 10 20 cm −3 . In summary, adding a 3 nm thick a-SiOx:H buffer layer with an intermediate band gap and with a p-type doping concentration (NA) below 10 18 cm −3 at the i/p interface improves the electrical and optical properties of the p-i-n solar cells (E FF = 8.951%; V OC = 0.994 V; FF = 83.1%; J SC = 10.842 mA.cm −2 ).