Large area rutile TiO2 nanorod arrays were grown on F:SnO2 (FTO) conductive glass using a hydrothermal method at low temperature. CdSe quantum dots (QDs) were deposited onto single-crystalline TiO2 nanorod arrays by a chemical bath deposition (CBD) method to make a photoelectrode. The solar cell was assembled using a CdSe-TiO2 nanostructure as the photoanode and polysulfide solution as the electrolyte. The annealing effect on optical and photovoltaic properties of CdSe quantum-dots-sensitized TiO2 nanorod solar cells was studied systematically. A significant change of the morphology and a regular red shift of band gap of CdSe nanoparticles were observed after annealing treatment. At the same time, an improved photovoltaic performance was obtained for quantum-dots-sensitized solar cell using the annealed CdSe-TiO2 nanostructure electrode. The power conversion efficiency improved from 0.59% to 1.45% as a consequence of the annealing effect. This improvement can be explained by considering the changes in the morphology, the crystalline quality, and the optical properties caused by annealing treatment.
SnO 2 compact layer (c-SnO 2 ) frequently suffers from degradation in high temperature processes (HTP) such as crack, worse interfacial contact, and electrical properties, that is, annealing effect. To solve this problem, a kind of bifunctional SnO 2 colloid is developed by using small molecular oxalate whose organic components can be removed clearly at a low temperature process (LTP). The c-SnO 2 and SnO 2 mesoporous layer (m-SnO 2 ) derived from the fresh and aged sols with the same colloid show no annealing effect, decreasing oxygen vacancy, and adsorbing water on increasing annealing temperature. The champion devices of LTP and HTP SnO 2 planar perovskite solar cells (PSCs) achieve, respectively, stabilized photoelectric conversion efficiencies (PCEs) of 20.74% and 20.70%. In contrast, the performance of champion devices of their mesoporous counterparts is significantly improved, showing nearly hysteresis free character with stabilized PCEs of 22.40% and 22.37%, respectively. The inclusion of m-SnO 2 plays a role of an energy bridge, improving electrons collection efficiency, which is supported by photoluminescence and transient photoluminescence characterizations. HTP SnO 2 mesoporous PSCs can preserve 97.6% and 80% of their initial PCEs after aging for 25 weeks and 8-h irradiated/16-h dark cycle within 104 h. The high stability of HTP SnO 2 PSCs may ascribe to low oxygen vacancy and adsorbed water of HTP SnO 2 .
2D transition metal dichalcogenides (TMDCs) nanocrystals and related semiconductor–metal heterostructures are promising new materials for efficient opto-electrical conversion because of their unique physical and chemical properties. The design and optimization of such materials require the understanding of exciton and charge carrier dynamics. The illumination-dependent carrier dynamics of CdS/MoS 2 heterostructure nanocrystals (CdS/MoS 2 HNCs) film is investigated by employing the voltage-current test, in which the CdS nanocrystals (NCs) film is used as a reference. The photocurrent performance of carriers in the CdS/MoS 2 HNCs is 70 times higher than that in CdS NC film, owing to the excellent interfacial hole transfer from the CdS component to the monolayer MoS 2 in CdS/MoS 2 HNCs, which effectively reduces the bulk and surface charger recombination. It means that the remaining electron in CdS component after hole transfer plays an important role in the final photocurrent performance. The annealing effect also plays a positive role in the photocurrent performance of nanocrystal film for CdS/MoS 2 HNC and CdS NC film. In addition, the transient absorption test is also used to exclude the possibility of interfacial electron transfer. The final results suggest that the construction of nano-heterojunction can affect the carrier dynamics of nanomaterials and enhance light responsiveness, which is conductive to the design and application of photovoltaic devices in the future.
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