Decoupling charge carrier collection and metallization geometry of back-contacted back-junction silicon solar cells by using insulating thin films

Abstract

Back-contacted back-junction silicon solar cells with a large emitter coverage (point-like base contacts) and a small emitter coverage (point-like emitter and base contacts) have been fabricated and analyzed. These solar cells feature an insulating thin film on the rear side in order to decouple the charge carrier collection geometry and the geometry of the metallization. It has been found, that for the investigated solar cells an increased collection efficiency is observed due to a significant reduction of electrical shading losses. Thus, high short-circuit currents could be achieved for both solar cell structures. Different insulating thin films, such as ALD Al2O3 and PECVD SiOx have been investigated. It has been found that ALD layers are already insulating for a thinner film thickness. By applying these insulating thin films to the investigated solar cell structures no significant shunts are introduced. For solar cells on 1 Ωcm n-type material and with a large emitter coverage an efficiency of 21.9% (Voc = 673 mV, Jsc = 40.6 mA/cm2, FF = 80.1%) could be obtained and for solar cells with a small emitter coverage an efficiency of 22.7% (Voc = 706 mV, Jsc = 41.0 mA/cm2, FF = 78.5%) has been achieved.