Rear junction laser doped solar cells on CZ n-type silicon

Abstract

N-type silicon (Si) has been shown to have generally higher bulk lifetimes and far better post illumination performance stability compared to boron doped p-type materials of similar crystallographic quality. In particular, the high minority carrier diffusion lengths in n-type wafers makes the rear emitter n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> np <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> structure an attractive option, especially when incorporated with screen printing as a simple and cost effective way to create an Al-alloyed junction on the back surface. However, when screen printing is used to apply the front contacts, its wide metal lines and its requirement for a heavy Phosphorus-doped front surface significantly reduces the performance of this simple device with the latter limiting the blue wavelength response and surface passivation quality. Recently, the laser doping process has been shown capable of overcoming these major drawbacks due to its ability to produce a selective emitter. In this present work, an innovative application of the laser doping process in the fabrication of such rear Al-alloyed emitter n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> np <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> device enables an excellent energy conversion efficiency of 18.2% to be achieved on commercial grade n-type CZ wafers (148.6cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ).