The passivation quality at the interface between liquid-phase crystallized silicon (LPC-Si) and a dielectric interlayer (IL) was investigated in terms of the defect state density at the IL/LPC-Si interface (Dit) as well as the effective fixed charge density in the IL (QIL,eff). Both parameters were obtained via high-frequency capacitance–voltage measurements on developed metal–insulator–semiconductor structures based on a molybdenum layer sandwiched between the IL and the glass substrate. Dit and QIL,eff were correlated to the open circuit voltage (Voc) and the integrated external quantum efficiency (Jsc,EQE) obtained on corresponding solar cell structures as well as to Voc and Jsc,EQE results based on two-dimensional simulations. We found that Dit was reduced by one order of magnitude using a hydrogen plasma treatment (HPT) at 400 °C. Irrespectively of the HPT, QIL,eff was > 1012 cm−2. We suggest that field-effect passivation dominates chemical passivation at the IL/n-type LPC-Si interface. We attribute the significant enhancement of Voc and Jsc,EQE observed after HPT on n-type LPC-Si solar cells mainly to improvements of the passivation quality in the n-type LPC-Si bulk rather than at the IL/n-type LPC-Si interface. For p-type absorbers, the HPT did not improve Voc and Jsc,EQE significantly. We propose that this is because of an insufficient passivation of bulk defects by positively charged hydrogen, which dominates in p-type silicon, in combination with an insufficient interface passivation. Copyright © 2016 John Wiley & Sons, Ltd.