Contact resistivity measurements and their applicability for accurate series resistance breakdown in heterojunction solar cell

In this work, we use several approaches to perform accurate Series Resistance (RS) breakdown of a state of the art 2 cm x 2 cm screen-printed solar cell reaching 82.5% FF. On the one hand, Haschke et al.'s model for the lateral transport through the cell, coupling the TCO and wafer sheet resistances through the contact resistivity (ρC), predicts a reduction of RS with increasing injection (Δn) through the enhanced wafer conductivity [Haschke et al., J. Appl. Phys., 2020]. In contrast, we observe that the RS of the solar cell, obtained from the difference between the J-V and Jsc-Voc curves, increases with Δn. Similarly, Senaud et al. observed increasing ρC with Δn using TLM measurements under illumination [Senaud et al., EU-PVSEC, 2020]. To investigate the discrepancy between these experimental observations and theoretical expectations, we extract ρC values either from dark TLM, illuminated TLM or illuminated symmetrical sample measurements and incorporate them into Haschke et al.'s model to reconstruct the RS of the solar cell. Detailed series resistance breakdown using pC values from all three tested methods show accurate RS predictions within at MPP ±0.1Ω.cm2, showing that the different approaches have sufficient accuracy to estimate the resistive losses in the solar cell under study. Regarding dependence upon injection, it was only possible to predict an increasing series-resistance trend using contact resistivity from illuminated TLM, therefore matching closer the measured linear increase of the RS of the solar cell from MPP to open circuit conditions, while the other methods predicted a decreasing trend. We discuss practical differences between the methods and propose possible improvements.