Characterization of carrier transport using a bifacial structure for rational design of p-n junction PbS solar cells

Abstract

In this study, a difference in the mobility of holes and electrons as a minority carrier has been systematically characterized in PbS quantum dot (QD) solar cells. While the mobility of electrons and holes is important in designing the p-n junction solar cells, it is still challenging to measure them during the normal operation of QD solar cells. When the solar includes only one transparent contact, it is difficult to separate the transport of electrons from that of holes during the normal operation of the device. We fabricated the bifacial solar cells and characterized the carrier transport by measuring the decay of photocurrent under pulsed illumination. The electron and hole mobility of p-type, n-type, and p-n junction type PbS QD film was examined and its connection to the performance of the solar cells was studied. In n-type PbS layer, the diffusion length of both electron and hole is ∼300 nm. In contrast, the diffusion length of hole and electron of p-type PbS layer is 250 nm and 175 nm. The asymmetric charge kinetics between holes and electrons in p-type PbS is systematically discussed. This result offers a rationale design rule of p-n junction type QD solar cells. 1) A difference in the mobility of holes and electrons is measured. 2) In n-type PbS layer, the diffusion length of both electron and hole is ∼300 nm 3) In p-type PbS, the asymmetric charge kinetics between holes and electrons is observed. 4) This study guides the design of the p-n junction type solar cells.