Two types of silicon (Si) substrates (40 n-type with uniform base doping and 40 n/n(+) epitaxial wafers) from the silicon industry rejects were chosen as the starting material for low-cost concentrator solar cells. They were divided into four groups, each consisting of 20 substrates: 10 are n/n(+) and 10 are n substrates, and the solar cells were prepared for different diffusion times (45, 60, 75 and 90 min). The fabricated solar cells on n/n(+) substrates (prepared with a diffusion time of 75 min) showed better parameters. In order to improve their performances, particularly the fill factor, 20 new solar cells on n/n(+) substrates were fabricated using the same procedure (the diffusion time was 75 min)-but with four new front contact patterns. Investigation of current-voltage (I-V) characteristics under AM 1.5 showed that the parameters of these 20 new solar cells have improved in comparison to previous solar cells' parameters, and were as follows: open-circuit voltage (V-OC = 0.57 V); short circuit current (I-SC = 9 10 mA), and efficiency (eta = 9.1%). Their fill factor has increased about 33%. The I-V characteristics of these solar cells were also investigated under different concentration ratios (X), and they exhibited the following parameters (under X = 100 suns): V-OC = 0.62 V and I-SC = 36 A. (C) 2004 Elsevier Ltd. All rights reserved.