Investigation of laser contact opening pitch affecting the void formation on n-Type rear emitter silicon solar cells

Abstract

The pitch of the rear side laser contact opening (LCO) strongly influences the performance of n-type Passivated Emitter and Rear Totally diffused (n-PERT) solar cells. The rear emitter of a back junction (BJ) cell was formed by boron doping [1,2]. The considered n-PERT, BJ cell structure is based on a p-type passivated emitter and rear cell (p-PERC) process sequence [3] upgraded by a boron diffusion on the rear side. Due to the application on n-type substrates, the cells have no light-induced degradation (LID) [4]. In this work we focus on fine tuning the LCO pitch of the device. We found that the LCO pitch directly affected the quality of the contact formation, leading to a variation on the solar cell performance investigated. By combined electroluminescence (EL) and photoluminescence (PL) measurements. Voids were identified (It’s about 60 μm width, 25 μm depth.) by scanning electron microscopy (SEM) and confirmed the different nature of the defects contributing to EL and PL contrast. Void formation is attributed to the diffusion of Si and Al at the Si/Al metallization interface. We found that void formation can be controlled by different LCO pitches. Based on this result we achieved a 0.35% absolute efficiency gain in average.