Inkjet printing of phosphorus dopant sources for doping poly-silicon in solar cells with passivating contacts

Abstract

In this work application of inkjet printing of phosphorus inks as dopant source for fabrication of silicon solar cells with tunnel oxide passivating contacts (TOPCon) was demonstrated. Inkjet printing is of great importance for the formation of selectively doped TOPCon layers of industrial TOPCon cells to provide a low contact resistance, while creating the requirements for screen printing metallization. Rheological characterizations were carried out in order to determine the complex viscosity and elastic effects of the inks. Printing processes were developed and optimized accordingly, given the significant relevance of rheology in inkjet printing. It was realized that inkjet printing processes have a direct influence on the electrical properties of passivating contacts. Droplets with a diameter of below 35 μm and lines with sharp edges and width of down to 70 μm were obtained. Excellent passivation quality was achieved for inkjet-printed n-type poly-Si surfaces with an implied open-circuit voltage of iVoc = 733 mV and an implied fill factor of iFF = 86.4%. For n-type passivating contacts, doped by inks containing phosphorus, the junction characteristics were investigated using double-sided contacted silicon solar cells. With these cells, Voc = 703 mV, FF = 72 %, and conversion efficiency of η = 17.1 % were realized. For ion-implanted poly-Si surfaces, herein used as reference, η = 18.2 % was obtained, underlining the high potential of investigated inkjet printing processes.