The overdependence on the tradition energy source have caused a serious of ecologi-cal problems such as the increasing emission of carbon dioxide. To combat this and achieve carbon neutrality, attention has shifted towards sustainable energy, particu-larly wind, tidal, and solar energy. The solar cell catches significant interest due to its ability to directly convert solar energy into electricity through the photovoltaic (PV) effect. The silicon heterojunction (SHJ) cells got a lot of attention with high efficiency and simple fabrication process. The record efficiency of SHJ solar cell is 26.81% from Longi [1]. The fabrication process for SHJ solar cells involves the use of plasma en-hanced chemical vapor deposition (PECVD). However, the use of toxic and flammable gases in the doping process poses safety risks in laboratories. The parasitic absorption introduced by a doped layer, leads to drawbacks in solar cell performance. Conse-quently, alternative materials like dopant-free carrier selective contacts (CSCs), divided into hole transport layers (HTL) and electron transport layers (ETL), have attracted con-siderable interest. Transition metal oxides (TMO) and metal fluorides stand out in do-pant-free material research.
This study investigates three metal fluorides (LiF, MgFX, and SrFX) as ETL in SHJ solar cells. Initially, four plasma treatments (PTP, PT, PTB, and noPT) are examined as inter-face treatments in combination with LiF as ETL in SHJ solar cells. Results indicate that PTP is the most compatible with LiF, yielding the highest efficiency. Additionally, stud-ying the impact of LiF thickness on cell performance reveals that a 1 nm thickness shows higher Voc and FF, resulting in higher efficiency. Further exploration into the deposition order of transparent conductive oxide (TCO) and LiF highlights that depos-iting LiF on the rear side preserves passivation properties, ensuring device perfor-mance. Investigations into metal electrode contacts on the rear side reveal that a sput-tered Ti/Ag contact with LiF provides the best performance due to its no-venting dep-osition process. On the front side, copper plating proves superior to screen printing due to better-controlled grids and a less aggressive process, benefiting cell perfor-mance.
We expand the optimal parameters obtained from previous experiments to MgFX and SrFX. We explore the thickness influence on cell performance. The optimal thickness of MgFX and SrFX are 1 nm and 4 nm, respectively. Finally, SHJ solar cells integrated with MoOX as HTL and LiF, MgFX, and SrFX as ETL show significant improvement in light response within the 300-600 nm wavelength range. The combination of MgFX/MoOX yields the highest efficiency, with the champion device exhibiting 716 mV of Voc, 38.02 mA/cm2 of Jsc, 76% of FF, and 20.69% efficiency, surpassing reported efficiencies within the same cell structure.