DopLa Solar Cells with Texturized Front Surface

Abstract

In this work, we report on improving efficiency of DopLa cells fabricated on p-type substrates. This type of solar cells has all the highly-doped regions based on laser doping from dielectric films resulting in a very simple fabrication process. Depending on the dopant type, emitter regions or high/low doping junctions related to base contacts can be created. The emitter regions are located at the rear surface in order to be contacted by a continuous metal film without penalizing in shadowing losses, while the front surface shows a typical finger grid configuration with the base contacts under the metal. In a previous work, the reported efficiency was limited by optical losses at the front planar surface. As a consequence, we focus on the introduction of a texturized front surface to the device. Firstly, we characterize the contact formation by laser processing on texturized surfaces by SEM image showing that the size of the contacted region is difficult to determine. By measuring contact resistance and surface recombination velocity, we deduce that the laser process of such surfaces leads to a contacted region which is smaller than the one where passivation is lost. The obtained information is included in 3D simulations to get the optimum size of the contacts, i.e. optimum laser power. Additionally, a new front grid metallization is introduced in order to reduce shadowing. Due to the rear emitter configuration of these devices, front surface recombination is crucial for collecting photogenerated carriers. Thus, optimum laser power is very close to the minimum to obtain a reliable contact. Finally, 2x2 cm2 solar cells are fabricated with a best efficiency of 17.0%.