Al0.3Ga0.7As/GaAs concentrator solar cells

An Al 0.3 Ga 0.7 As/GaAs tandem solar cell was fabricated in a commercial reactor which has been specially modified for dual operation of both atomic layer epitaxy (ALE) and metalorganic chemical vapor deposition (MOCVD) growth modes. The p-type and n-type dopants were carbon and silicon, respectively, and the required doping concentrations were achieved by optimizing growth conditions such as V/III ratio (mole ratio of group V atoms to group III atoms), exposure times to reactant gases, and growth temperatures. The current-voltage (I-V) characteristics indicate that, up to 53 Suns, the tunnel junction does not seem to result in any appreciable deterioration in the multijunction solar cell's performance. The measured efficiency increases with increasing solar concentration up to a point where a region of negative resistance starts to appear in the I-V characteristics.