Fig. 1: Engineering the microscopic nature of the matrix to increase the ordering and photocarrier diffusion length in CQD solids for solar cells.
From: 2D matrix engineering for homogeneous quantum dot coupling in photovoltaic solids
a, Schematic diagram of the effective medium model of the CQD absorber in a solar cell, where CQDs (red) assemble in a matrix medium (blue). b, In published best-performing PbS CQD PV solids, the matrix component is PbI2 and its amount is ~40–50% compared with PbS in a molecular ratio, enough to account for the formation of a full monolayer coverage on the surfaces of the PbS CQDs (bandgap ~1.3 eV and diameter ~3 nm). c, DMF and hybrid amines are used to functionalize the PbI2 matrix component and tailor the matrix’s microstructure and distribution during the reorganization that occurs when the CQDs are solidified from solution. The PbI2–hybrid-amine coordinating complex has a self-confined 2D layered structure that greatly suppresses inhomogeneity of the matrix due to a random 3D growth in DMF. d, Inhomogeneity of the matrix increases the structural and energetic disorder and reduces the diffusion length and VOC. CQD over isolation due to local matrix agglomeration will block the carrier transport. CQD overcoupling due to surface fusion caused by the absence of the matrix tends to increase the VOC deficit. e, Confining the matrix dimensionality between the CQDs and improving its homogeneity throughout the film increases the photocarrier diffusion length and reduces the VOC deficit. HTL; hole-transport layer; EDT; 1,2-ethanedithiol; ETL, electron-transport layer; ITO, indium tin oxide; CB, conduction band; E, energy.
