Paths for maximal light incoupling and excellent electrical performance in silicon heterojunction solar cells
Mathieu Boccard1, Luca Antognini1, Jean Cattin1, Julie Dréon1, Olivier Dupré1, Angela Fioretti1, Jan Haschke1, Raphaël Monnard1, Vincent Paratte1, Esteban Rucavado1, Laurie-Lou Senaud2, Sihua Zhong1, Bertrand Paviet-Salomon2, Monica Morales-Masis1, Matthieu Despeisse2, Christophe Ballif1,2
1EPFL, Neuchâtel, Switzerland
/2CSEM, Neuchâtel, Switzerland

We review here recent progress on high-efficiency, high-current silicon heterojunction solar cells. We give several industry-relevant paths towards simultaneous reaching of high current densities and excellent electrical properties, both for 2-side-contacted and interdigitated-back-contacted (IBC) devices. For the latter, record efficiencies were demonstrated in recent years, yet with non-industrially-viable processes. We discuss here progress in tunnel IBC architecture—showing extraordinary simple process with a one-mask and one-alignment approach—still demonstrating efficiency values above 24%. We reveal here some key requirements to combine highly crystalline doped layers with excellent passivation enabling high voltages and low series resistance. For 2-side contacted solar cells, we will review progress on transparent electrodes and contact layers, that allows improving light management (with Jsc > 40 mA/cm2 in each individual case) while maintaining passivation and reducing resistive losses. Zr-doped In2O3 provides improved transparency both in the UV and IR parts of the spectrum thanks to a high carrier density and mobility. Thin yet high-crystallinity microcrystalline silicon doped layers provide lower absorption and advantageous refractive index matching compared to amorphous silicon, together with improved electrical properties. Finally, recent results on metal-oxide-based electron and hole-selective contacts (including ZnO and MoOx) will be discussed.