Nanocomposite Photoanodes Consisting of p-NiO/n-ZnO Heterojunction and Carbon Quantum Dot Additive for Dye-Sensitized Solar Cells

Abstract

To increase the performance of power conversion efficiency of dye-sensitized solar cells (DSSCs), in the current paper, nanocomposites of n-type ZnO and p-type NiO semiconductors were constructed as photoanodes in DSSCs. Furthermore, the influence of the addition of carbon quantum dots on the nanocomposites of n-ZnO and p-NiO was evaluated. The efficiency achieved was 1.58 times of that of ZnO with addition of 8 wt % NiO. Moreover, the doping of carbon quantum dots in the nanocomposites of ZnO/NiO­(8 wt %) enhanced the efficiency up to 3.8 times of that of ZnO/NiO­(8 wt %). The value (13.02% (430 nm LED@100 W/m2)) was the highest among that of the carbon dot-incorporating DSSCs. NiO and ZnO semiconductors created a p–n heterojunction, gave rise to faster separation of charges, and minimized the recombination of electrons. Carbon quantum dots promoted the charge carrier transport by converting photon to charge and reducing the potential barrier of the charge carrier at the interfaces of n-ZnO/carbon dots and carbon dots/p-NiO. These results suggest that the adequate selection of the band gap energy levels of the materials induces the preferable charge separation. Especially, the effect reducing the potential barrier of charge carriers by carbon quantum dots is prominent to improve the photovoltaic efficiency of the DSSCs. Thus, the nanoscale materials of ZnO, NiO and Cdots were promising for the enhancement of photovoltaic performance.

A transparent photovoltaic device of NiO/MgO quantum dots/TiO2 arrays pn junction with carrier injection of MgO QDs

“…Fig. S3 (ESI) is the I-V curve of as-prepared transparent NiO/MgO QDs/TiO 2 pn junction device (NiO/TiO 2 -MgO-2) in dark and illumination, as demonstrated, and this asprepared sample in dark exhibits a typical rectification and exhibits a shift down and higher response in illumination, which manifest that this as-prepared transparent device is a typical pn junction [10,11,18,37,39,40,60]. Additionally, more detailed performance would be evaluated as follows.…”

“…As reported, the Ni 3? induced by Ni vacancy and interstitial O produced during the preparation would activate the hole-related charge carriers, which is the core issue for the intrinsic p-type conductivity of NiO [11,39,40].…”

“…Up to now, lots of remarkable p-type transparent semiconductors have been reported [35,36], for instance, CuAlO 2 , SnO or Cu 2 O, etc. Herein, the NiO [37,38], with widely band gap and a mass of intrinsic holes charge carriers, can exhibit high transparency and p-type conductivity simultaneously, such as Reddy and Bon groups have prepared the p-NiO/n-CdS:Al self-powered photodetector [39] and Geleta and Imae have fabricated the p-NiO/n-ZnO heterojunction for improving solar cells [40]. Additionally, during the preparation process, the produced Ni vacancy and interstitial O would induce the formation of Ni 3?…”

Carbon Quantum Dots for Energy Applications: A Review

“…The resulting CDs-modified TiO 2 @CDs/N719 device exhibited a PV efficiency of 7.32%, which was more than that of the untreated device (3.25%) . Geleta and Imae fabricated highly efficient p–n heterojunction DSSCs by introducing CQDs as an additive in the p-NiO/n-ZnO film . The p–n heterojunction alignment contributed to the effective separation of the electron–hole and promoted the photon-to-charge conversion and rapid charge-transfer kinetics.…”

“…Tesfaye et al fabricated highly efficient p-n heterojunction DSSCs by introducing CQDs as an additive in the p-NiO/n-ZnO film 160. The p-n heterojunction alignment contributed to the effective separation of the electron-hole and promote the photon-to-charge conversion and rapid charge transfer kinetics.…”