A planar nanostructure inserted by P-ion implantation within a silicon wafer transforms its optical and electronic properties, An amorphized substructure with abrupt a-Si/c-Si interfaces is formed. Recently, a solar-efficiency improvement by superposition of the a-Si and c-Si phases has been shown, thanks to the so-called HIT design. In this paper, we report on a large internal quantum efficiency (IQE) improvement in the near-IR (lambda > 900 nm) for a series of multi-interface solar cell models. The IR-IQE modification is due, on the one hand, to increased I R absorption and on the other hand, to photogeneration in the presence of thermal phonons via an extrinsic energy band that results from the useful post-implantation defects in the cell. We show that the near-IR modification changes with ambient temperature. This could be related to an evolution of the phonon energy distribution, which would increase the probability of carrier generation with the participation of phonons. (C) 2002 Elsevier Science B.V. All rights reserved.