In this contribution, we study the effects of NaLuF₄:Yb,Tm nanorods (NRs) dopant on the performance of inverted polymer bulk heterojunction (BHJ) solar cells. The study allows us to investigate the impact of NRs on the light-harvesting and photocurrent in BHJ solar cells fabricated with PCDTBT blended with [6,6]-phenyl-C71-butyric acid methylester (PC₇₁BM) acceptor. By controlling the doping concentrations, we demonstrate that the power conversion efficiency (PCE) of PCDTBT:PC₇₁BM solar cells increases from 6.02% to 7.18% mainly due to improving light absorption and photocurrent. The single carrier devices reveal that the electron and hole mobilities both rise in doped devices, contributing to the enhancement of photoconductivity and consequent PCEs.