AbstractReducing the optical losses and increasing the reflection while maintaining the function of doped layers at the back contact in solar cells are important issues for many photovoltaic applications. One approach is to use doped microcrystalline silicon oxide (μc‐SiOx:H) with lower optical absorption in the spectral range of interest (300 nm to 1100 nm). To investigate the advantages, we applied the μc‐SiOx:H n‐layers to a‐Si:H single junction solar cells. We report on the comparison between amorphous silicon (a‐Si:H) single junction solar cells with either μc‐SiOx:H n‐layers or non‐alloyed silicon n‐layers. The origin of the improved performance of a‐Si:H single junction solar cells with the μc‐SiOx:H n‐layer is identified by distinguishing the contributions because of the increased transparency and the reduced refractive index of the μc‐SiOx:H material. The solar cell parameters of a‐Si:H solar cells with both types of n‐layers were compared in the initial state and after 1000 h of light soaking in a series of solar cells with various absorber layer thicknesses. The measurement procedure for the determination of the solar cell performance is described in detail, and the measurement accuracy is evaluated and discussed. For an a‐Si:H single junction solar cell with a μc‐SiOx:H n‐layer, a stabilized efficiency of 10.3% after 1000 h light soaking is demonstrated. Copyright © 2015 John Wiley & Sons, Ltd.