Jianjun Tian

A highly efficient (>6%) Cd1−xMnxSe quantum dot sensitized solar cell

Quantum dot sensitized solar cells (QDSCs) have attracted considerable attention recently and become promising candidates for realizing a cost-effective solar cell. The design and synthesis of quantum dots (QDs) for achieving high photoelectric performance is an urgent need imposed on scientists. Here, we have succeeded in designing a QDSC with a high efficiency η of 6.33% based on Cd0.8Mn0.2Se quantum dots by facile chemical bath deposition (CBD). The effects of Mn2+ ions on the physical, chemical, and photovoltaic properties of the QDSCs are investigated. The Mn2+ ions doped into QDs can increase the light harvesting to produce more excitons. In addition, the Mn2+ dopant also raises the conduction band of CdSe, accelerates the electron injection kinetics and reduces the charge recombination, improving the charge transfer and collection. The increase of the efficiencies of light-harvesting, charge-transfer and charge-collection results in the improvement of the quantum efficiency of the solar cells. The power conversion efficiency of the solar cell is increased to 6.33% (Voc = 0.58 V, Jsc = 19.15 mA cm−2, and FF = 0.57).

Architectured ZnO photoelectrode for high efficiency quantum dot sensitized solar cells

In this work, we reported a facile chemical passivation strategy for a ZnO mesoporous photoelectrode to improve the performance of a CdS/CdSe quantum dot co-sensitized solar cell (QDSC). The QDSC exhibited a record power conversion efficiency of 4.68%.

Control of Nanostructures and Interfaces of Metal Oxide Semiconductors for Quantum-Dots-Sensitized Solar Cells

Nanostructured metal oxide semiconductors (MOS), such as TiO2 and ZnO, have been regarded as an attractive material for the quantum dots sensitized solar cells (QDSCs), owing to their large specific surface area for loading a large amount of quantum dots (QDs) and strong scattering effect for capturing a sufficient fraction of photons. However, the large surface area of such nanostructures also provides easy pathways for charge recombination, and surface defects and connections between adjacent nanoparticles may retard effective charge injection and charge transport, leading to a loss of power conversion efficiency. Introduction of the surface modification for MOS or QDs has been thought an effective approach to improve the performance of QDSC. In this paper, the recent advances in the control of nanostructures and interfaces in QDSCs and prospects for the further development with higher power conversion efficiency (PCE) have been discussed.

Hierarchically structured ZnO nanorods-nanosheets for improved quantum-dot-sensitized solar cells.

ZnO nanorods (NRs) and nanosheets (NSs) were fabricated by adjusting the growth orientation of ZnO crystals in the reaction solution, respectively. The thin ZnO NSs were slowly assembled on the surface of NRs to form a hierarchically structured NR-NS photoelectrode for constructing CdS/CdSe quantum-dot-sensitized solar cells (QDSCs). This hierarchical structure had two advantages in improving the power conversion efficiency (PCE) of the solar cells: (a) it increased the surface area and modified the surface profile of the ZnO NRs to aid in harvesting more quantum dots, which leads to a high short-current density (Jsc); (b) it facilitated transportation of the electrons in this compact structure to reduce the charge recombination, which led to enhancement of the open-circuit voltage (Voc) and fill factor (FF). As a result, the QDSC assembled with the hierarchical NR-NS photoelectrode exhibited a high PCE of 3.28%, which is twice as much as that of the NR photoelectrode (1.37%).

Semiconductor quantum dot-sensitized solar cells

Semiconductor quantum dots (QDs) have been drawing great attention recently as a material for solar energy conversion due to their versatile optical and electrical properties. The QD-sensitized solar cell (QDSC) is one of the burgeoning semiconductor QD solar cells that shows promising developments for the next generation of solar cells. This article focuses on recent developments in QDSCs, including 1) the effect of quantum confinement on QDSCs, 2) the multiple exciton generation (MEG) of QDs, 3) fabrication methods of QDs, and 4) nanocrystalline photoelectrodes for solar cells. We also make suggestions for future research on QDSCs. Although the efficiency of QDSCs is still low, we think there will be major breakthroughs in developing QDSCs in the future.

Constructing ZnO nanorod array photoelectrodes for highly efficient quantum dot sensitized solar cells

This work reports on a ZnO nanorod (NR) array photoelectrode for CdS/CdSe quantum dot cosensitized solar cells (QDSCs), which generated a high power conversion efficiency of 3.14%. ZnO NR arrays were fabricated by growing on a seeded indium-doped tin oxide (ITO) substrate without using a template or high temperature conditions. The ZnO NR served as the backbone for direct electron transport in view of its single crystallinity and high electron mobility. To improve the performance of the QDSC, we introduced a facile chemical surface modification of the ZnO NR array photoelectrodes. The chemical processing not only formed a barrier layer of TiO2 nanoparticles on the surface of the ZnO NR, which suppresses charge recombination by preventing the electrons in the ZnO conduction band from transferring to the oxidized ions in the electrolyte, but also modified the surface characteristics of the ZnO NR so as to harvest a greater amount of QDs and increase the short current density of the QDSC. As a result, the QDSC assembled with the modified ZnO NR array photoelectrode exhibited a high performance with Jsc, Voc, FF and η performance values equal to 9.93 mA cm−2, 0.61 V, 0.52 and 3.14%, respectively.

Rapid construction of TiO2 aggregates using microwave assisted synthesis and its application for dye-sensitized solar cells

Hierarchical TiO2 nanocrystallite aggregates, composed of ∼10 nm nanocrystallites, with a size of ∼500 nm have been synthesized by a microwave assisted method at 150 °C in a short time (∼10 minutes) as the photoanode of dye-sensitized solar cells (DSCs). Ethanol and TiCl4 are selected as the solvent and titanium precursor, respectively. The rapid heating rate and superheating/“hot spots” of the reaction system under microwave irradiation result in a large amount of nuclei instantly, which leads to the formation of a great deal of clusters. Moreover, the clusters that grow up rapidly are assembled into TiO2 nanocrystallite aggregates. The TiO2 aggregates show better light scattering property, larger specific surface area and higher dye-loading compared to the commercial P25 TiO2 nanoparticles. In comparison with DSC based P25 photoanode, the short current density (Jsc) and dye-loading of DSC based the as-synthesized TiO2 aggregates photoanode increase by 33% and 62%, respectively. As a result, the PCE of the DSC is up to 7.64%, and the TiO2 aggregates obtained by microwave assisted synthesis are a promising and potential candidate for DSCs.

Enhanced Performance of PbS-quantum-dot-sensitized Solar Cells via Optimizing Precursor Solution and Electrolytes.

This work reports a PbS-quantum-dot-sensitized solar cell (QDSC) with power conversion efficiency (PCE) of 4%. PbS quantum dots (QDs) were grown on mesoporous TiO2 film using a successive ion layer absorption and reaction (SILAR) method. The growth of QDs was found to be profoundly affected by the concentration of the precursor solution. At low concentrations, the rate-limiting factor of the crystal growth was the adsorption of the precursor ions, and the surface growth of the crystal became the limiting factor in the high concentration solution. The optimal concentration of precursor solution with respect to the quantity and size of synthesized QDs was 0.06 M. To further increase the performance of QDSCs, the 30% deionized water of polysulfide electrolyte was replaced with methanol to improve the wettability and permeability of electrolytes in the TiO2 film, which accelerated the redox couple diffusion in the electrolyte solution and improved charge transfer at the interfaces between photoanodes and electrolytes. The stability of PbS QDs in the electrolyte was also improved by methanol to reduce the charge recombination and prolong the electron lifetime. As a result, the PCE of QDSC was increased to 4.01%.

Constructing water-resistant CH3NH3PbI3 perovskite films via coordination interaction

Organic–inorganic halide CH3NH3PbI3 (MAPbI3) perovskite solar cells (PSCs) have attracted intensive attention due to their high power conversion efficiency and low fabrication cost. However, MAPbI3 is known to be very sensitive to humidity, and the intrinsic long-term stability of the MAPbI3 film remains a critical challenge. 2-Aminoethanethiol (2-AET) was used as a ligand to bridge the organic compound (MAI) and inorganic compound (PbI2), which restricted the fast growth of PbI2 to realize the synchronous growth environment of MAI and PbI2 crystals, resulting in the formation of a compact MAPbI3 film with polygonal grains. Due to the compact (PbI2)–2-AET–(MAI) molecule barrier layers in the MAPbI3 structure, the resulting perovskite films showed excellent intrinsic water-resistance, with the MAPbI3 perovskite crystal structure retained for a long time (>10 minutes) after immersion in water. This work makes a step towards obtaining long-term stable MAPbI3 perovskite devices.

Dynamic Growth of Pinhole-Free Conformal CH3NH3PbI3 Film for Perovskite Solar Cells.

Two-step dipping is one of the popular low temperature solution methods to prepare organic-inorganic halide perovskite (CH3NH3PbI3) films for solar cells. However, pinholes in perovskite films fabricated by the static growth method (SGM) result in low power conversion efficiency (PCE) in the resulting solar cells. In this work, the static dipping process is changed into a dynamic dipping process by controlled stirring PbI2 substrates in CH3NH3I isopropanol solution. The dynamic growth method (DGM) produces more nuclei and decreases the pinholes during the nucleation and growth of perovskite crystals. The compact perovskite films with free pinholes are obtained by DGM, which present that the big perovskite particles with a size of 350 nm are surrounded by small perovskite particles with a size of 50 nm. The surface coverage of the perovskite film is up to nearly 100%. Such high quality perovskite film not only eliminated pinholes, resulting in reduced charge recombination of the solar cells, but also improves the light harvesting efficiency. As a result, the PCE of the perovskite solar cells is increased from 11% for SGM to 13% for DGM.