Heterojunction Solar Cells With Buried Al Grids and Li₃PO₄ Electron Selective Contacts Approaching 24% Efficiency

Dopant-free materials with wide-bandgap are promising alternatives to n-type or p-type amorphous silicon (a-Si) contacts in silicon heterojunction (SHJ) solar cells. They offering strong carrier selectivity through favorable band alignment, negligible parasitic absorption, and full compatibility with low-temperature processing. However, implementing such contacts on the front side remains challenging because optical losses, contact resistivity, and gird patterns should be balanced carefully. Here, these constraints are overcome through an interfacial design that integrates a lithium phosphate (Li₃PO₄) electron-selective layer, a low-work function magnesium fluoride (MgF₂) anti-reflection coating, and a grid with buried Al/Li₃PO₄ contact. Upon annealing, the patterned metal grid confines Al diffusion to localized contact regions, while the MgF₂ overlayer promotes downward band bending at the c-Si interface. Meanwhile, phosphorus self-diffusion within Li₃PO₄ reduces the contact resistivity, and the recovery of hydrogen passivation in intrinsic a-Si:H further suppresses interfacial defect states. These effects yield an interface that combines excellent passivation with low resistive loss. As a result, the devices achieve a power conversion efficiency of 23.81% (V_OC = 715.2 mV, J_SC = 40.65 mA/cm², FF = 81.9%), representing the highest reported efficiency for SHJ solar cells with a front contact by dopant-free materials. This work highlights the potential of wide-bandgap compounds on the illuminated side and provides a viable route toward next-generation high-efficiency silicon solar technologies.