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In this paper, we provide experimental evidence of the effects of unintentional p-type doping on the performance and the apparent recombination dynamics of bulk-heterojunction solar cells. By supporting these experimental observations with drift-diffusion simulations on two batches of the same efficient polymer-fullerene solar cells with substantially different doping levels and at different thicknesses, we investigate the way the presence of doping affects the interpretation of optoelectronic measurements of recombination and charge transport in organic solar cells. We also present experimental evidence on how unintentional doping can lead to excessively high apparent reaction orders. Our work suggests first that the knowledge of the level of dopants is essential in the studies of recombination dynamics and carrier transport and that unintentional doping levels need to be reduced below approximately 7 × 1015 cm-3 for full optimization around the second interference maximum of highly efficient polymer-fullerene solar cells., F. D. and J. R. D. are thankful of the support from the EPSRC APEX Grant No. EP/H040218/2 and SPECIFIC Grant No. EP/1019278. T. K. acknowledges funding by an Imperial College Junior Research Fellowship. We are grateful to the Ministerio de Economa y Competitividad for funding through the project PHOTOCOMB, Reference No. MAT2012-37776.