Heterojunction Rear Passivated Contact for High Efficiency n-Cz Si Solar Cells

We investigate the challenges and potential for high-efficiency n-type Cz Si solar cells having a hybrid structure - a diffused B emitter on the front side, and an amorphous Si heterojunction (SHJ) passivated full-area contact on the rear. This cell design has benefits over comparable high-efficiency geometries such as PERL (passivated emitter rear locally diffused) and SHJ cells with heterojunctions both front and rear. We show that an advantage of the HJ rear contact is excellent passivation of the backside, with measured contact recombination current density J_0,b,c < 10 fA/cm²; moreover, compared to PERL, its cell fabrication process is much simpler. Weighed against standard SHJ cells, the diffused front results in less optical loss and no need for a transparent conducting oxide (TCO). We study the contact resistivity of a state-of-the-art SHJ rear contact to the wafer, finding a value of ∼0.3 ohm-cm²; a series of experiments are performed to reduce this value while maintaining potential for high V_oc > 700 mV. As an initial demonstration of the concept, we fabricate a hybrid-structure cell having V_oc = 671 mV, J_sc = 36.7 mA/cm², FF = 0.75 and efficiency of 18.5%.