Hybrid solar cells made of a p-type conducting polymer, poly(3,4-ethyl thiophene): polystyrenesulfonate (PEDOT:PSS), on Si have gained considerable interest in the fabrication of cost-effective high-efficiency devices. However, most of the high power conversion efficiency (PCE) performances have been obtained from solar cells fabricated on surface-structured Si substrates. High-performance planar single-junction solar cells have considerable advantages in terms of processing and cost, because they do not require the complex surface texturing processes. The interface of single-junction solar cells can critically influence the performance. Here, we demonstrate the effect of adding different surfactants in a co-solvent-optimized PEDOT: PSS polymer, which, in addition to acting as a p-layer and as an anti-reflective coating, also enhances the device performance of a hybrid planar-Si solar cell. Using time-of-flight secondary ion mass spectrometry, we conduct three-dimensional chemical imaging of the interface, which enables us to characterize the micropore defects found to limit the PCE. Upon minimizing these micropore defects with the addition of optimized amounts of fluorosurfactant and co-solvent, we achieve a PEDOT: PSS/planar-Si cell with a record high PCE of 13.3% for the first time. Our present approach of micropore defect reduction can also be used to improve the performance of other organic electronic devices based on PEDOT: PSS.