Edge effect in silicon solar cells with dopant-free interdigitated back-contacts

Dopant-free heterojunction opens new doors to highly efficient silicon solar cells with interdigitated back-contacts (IBC) via an easy hard-mask processing. However, the existence of inevitable overlap between the hole- and electron-transport layers may cause edge leakage and recombination, which will deteriorate the power conversion efficiency. Here we unambiguously determined the edge recombination and recombination losses quantitatively, in combination with detailed comparisons in photovoltaic parameters, dark and light current-voltage (I–V) curves, partially illuminated I–V curves, of the hard-mask processed and the lithography processed IBC devices. Without the interfacial passivation layer, the solar cells fabricated by the hard-mask method suffer severe edge recombination with loss of 3 × 10−4 A and a quite poor fill factor (FF) of ~66%, suggesting that the edge recombination could be another important issue affecting the FF besides the series resistance. With the clear understanding of the edge effect, we finely control the edge overlap, and finally obtained silicon dopant-free solar cells (with of intrinsic amorphous silicon as passivation layer) with over 20% efficiency and 73% FF either by lithography or by hard-mask methods.