Modification of a post-implantation defect activity for photovoltaic conversion

Abstract The problem of an eventual usefulness of defects and traps in solar cells (and especially in implanted Si material) has been investigated since the 1980s. Usually in place of an increase, the efficiency actually diminishes because of the non-radiative recombination on numerous defects. At the beginning of the 1990s a new approach was proposed. The fundamental difference concerns the thermodynamic aspects of devices: microelectronic and photovoltaic (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 optical activity (generation). PV characteristics depend simultaneously on optical (absorption, conversion) and electronic (carrier transport and collection) behaviour. We have analyzed theoretically and experimentally some possible 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. The results of the local crystalline modification have been compared with those obtained by spectral response. We show that an adequate implantation and annealing allow an important transformation of conversion, transport and collecting characteristics.