Modification of a post-implantation defect activity for photovoltaic conversion

The problem of an eventual usefulness of defects and traps in solar cells l and especially in implanted Si material) has been investigated since the 19 80s. Usually in place of an increase, the efficiency actually diminishes be cause of the nonradiative recombination on numerous defects. At the beginni ng of the 1990s a new approach was proposed. The fundamental difference con cerns the thermodynamic aspects of devices: microelectronic and photovoltai c (PV) which differentiates a receiver from a generator. In the solar cell, there is an additional dimension, i.e. optoelectronic properties where the electronic behaviour (recombination) can be completed/modified by an optic al activity (generation). PV characteristics depend simultaneously on optic al (absorption, conversion) and electronic (carrier transport and collectio n) behaviour. We have analyzed theoretically and experimentally some possib le modifications of the post-implantation defect activity on single-crystal Si in view of a very- and ultra-high PV conversion efficiency. The applied techniques can be classified as bandgap, defect and stress engineering. Th e results of the local crystalline modification have been compared with tho se obtained by spectral response. We show that an adequate implantation and annealing allow an important transformation of conversion, transport and c ollecting characteristics. (C) 1999 Elsevier Science B.V. All rights reserv ed.