Achievement of 25.54% power conversion efficiency by optimization of current losses at the front side of silicon heterojunction solar cells

Parasitic absorption in the front window layers of transparent conductive oxide (TCO) films and carrier selective collection layers and the optical shading losses from the metallic finger grid mainly limit the current generation in silicon heterojunction (SHJ) solar cells. In this work, we demonstrate an improved short-circuit current density (J(sc)) of 40.24 mA/cm(2) through a combination of novel window layers composed of transition metal doped indium oxide (IMO) and hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) films and Cu plating for SHJ solar cells. By introducing water vapor during direct current (DC) magnetron sputtering deposition process, IMO films show a large optical band gap (E-g) of about 3.88 eV and high mobility up to 83.2 cm(2)/V center dot s, while maintaining a low carrier concentration, which leads to high transparency and low near-infrared (NIR) free carrier absorption (FCA). In addition to its high deposition rate and crystalline volume fraction, we found that nc-SiOx:H films deposited by very high frequency (VHF) excited plasma-enhanced chemical vapor deposition (PECVD) show an excellent surface passivation quality, which not only improves the open circuit voltage (V-oc) of SHJ cells but also increases the J(sc) through improved carrier selective collection. The quantified J(sc) breakdown analysis was performed to identify the room for improvement, and it showed that the front shading loss (about 1.32 mA/cm(2)) is the largest portion. By combining the benefits of these window layer enhancements with the further use of fine line width and conductivity of Cu plating, SHJ solar cells, with a J(sc) improvement of 0.57 mA/cm(2) and a certified efficiency of 25.54%, were achieved on a total area of 274.5 cm(2) using in-house pilot production line equipment.