Design of Large Poly‐Si on Oxide Interdigitated Back Contact (POLO IBC) Silicon Solar Cells with Local Al–p ⁺ Contacts in the Constraints of Measurement and Module Integration

Interdigitated back contact (IBC) silicon solar cells with a passivating n-type poly-Si on oxide emitter and an aluminum-doped p⁺ base contact on M2-sized Ga-doped p-type Cz wafers are reported. The Al-doped base contact forms during the firing of the printed contacts and allows for a lean process flow. The device optimization balances recombination at the base contacts against resistive losses and respects constraints set by the need of interconnecting cells in a module and contacting the cells temporally by a measurement chuck. A special sample holder is designed for measuring the I_sc–V_oc curve of the IBC cell with a busbar-less metal grid. The pseudo-efficiency is 24.7%. All fingers of each polarity are connected with wires and an efficiency of 22.3% is measured. The comparison of simulations and measurements reveals that the cell has 23.4% efficiency without the series resistance losses due to the wires. A huge part of the resistive losses in the cell are the transport losses of the majorities in the base dissipating a power that corresponds to 0.76%_abs efficiency and the resistive losses at the Al-doped base contact (0.29%_abs).