A Si quantum dot (QD) heterojunction solar cell with a p-type Si QD layer on an n-type crystalline Si wafer was developed, and the effect of the boron (B)-doping profile in the Si QD layer was investigated. The doping concentration of B in the p-type Si QD layer was optimized at 5.71 x 10(21) atoms/cm(3), and high power conversion efficiency (PCE) of 14.15% was achieved at the optimized B concentration. A Si QD solar cell having a Si QD layer with a double-step B-doping profile was suggested to enhance the vertical charge carrier transport in the Si QD layer. As a result of the B-doping profile change from a single-step to double-step, the PCE of the Si QD solar cell was increased from 14.41% to 14.98%. In the Si QD solar cell with a double-step B-doping profile, quantum efficiency analysis showed that the improvement in short circuit current within short wavelength region under 650 nm can be related with the additional built-in E-field caused by the band structure modification. (C) 2016 Elsevier B.V. All rights reserved.