Charge separation and recombination in radial ZnO/In2S3/CuSCN heterojunction structures

Abstract

A ZnO-nanorod/In2S3/CuSCN radial hetero structure has recently shown promising photovoltaic conversion efficiencies. In this work, the charge separation and recombination in single ZnO/ In2S3 and In2S3/CuSCN interfaces as well as the complete ZnO/In2S3/CuSCN structure were studied by time resolved microwave photoconductivity. Photoconductivity transients were measured for different thicknesses of the In2S3 light absorbing layer, under variation of the exciting light flux and before and after annealing of the ZnO nanorods at 450°C. Upon excitation with 532nm light, a long lived (ms) charge separation at the In2S3/ZnO interface was found, whereas no charge separation was present at the In2S3/CuSCN interface. The presence of the CuSCN hole conductor increased the initial amplitude of the TRMC signal of the In2S3/ZnO interface by a factor of 8 for a 6nm thick In2S3 layer, but the enhancement in amplitude dropped strongly for thicker films. The measurements show that the primary charge separation is located at the In2S3/ZnO interface but the charge injection yield into ZnO depends critically on the presence of CuSCN.

Multiple-Trapping Governed Electron Transport and Charge Separation in ZnO/In2S3 Core/Shell Nanorod Heterojunctions

“…Afterward the decay slows down and crosses over to a slow hundreds of ps long rise. From the earlier experiments it is known that a long-lived (μs) charge separated state is formed in this material. Hence, the most natural explanation for the delayed rise is the migration of electrons from the In 2 S 3 phase to the ZnO phase.…”

“…Hence R ( t ) can be simplified to k 2 n 2 . It is also reasonable to assume that all photogenerated charge carriers have recombined on the interpulse time scale of 6.7 μs (due to the repetition rate of the laser) as the conductivity has completely vanished after that time …”

“…However, with an optimal shell thickness the external quantum efficiency can be close to unity . Recently, an optical-pump microwave-probe study on the radial ZnO/In 2 S 3 /CuSCN system identified the charge separation to occur at the ZnO-In 2 S 3 interface, lasting up to milliseconds. However, the low 10 ns time resolution prohibited a direct observation of both the charge carrier dynamics in the absorber as well as the charge separation at the ZnO–In 2 S 3 interface.…”

Flexible quantum dot sensitized solar cell by electrophoretic deposition of CdSe quantum dots on ZnO nanorods

“…Belaidi et al have pointed out that the variation of I-V parameters is related to the thickness of absorber on the ZnO surface. 16 In our case, the absorbance of the photoanode is increased with the increase in applied voltage, thereby leading to an increased J sc . With the increased thickness of CdSe QDs on the ZnO surface, the shunt resistance of the cell is largely increased, leading to a increase in V oc from 0.47 to 0.58 V, and FF from 29.9 to 47.4%.…”

“…The series resistance is increased, resulting in a decreased FF and PCE value due to the lower diffusion length of QD than that of the photo-generated charge carriers. 16 Therefore, the maximum PCE value of QDSSC is 0.74% with J sc = 2.70 mA cm…”