Chengbin Fei

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).

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.

Dye-sensitized solar cells based on hierarchically structured porous TiO2 filled with nanoparticles

A new morphology of TiO2 photoanodes for N-719 dye-sensitized solar cells (DSCs) has been developed with enhanced power conversion performance. Strategies for the synthesis of hierarchically structured three-dimensionally ordered macroporous (HS-3DOM) TiO2 with controlled macropore sizes (ca. 85–155 nm) by using well-arrayed polymethyl methacrylate with different diameters as well as two kinds of photoanode films based on hierarchically structured porous TiO2 filled with nanoparticles have been demonstrated. DSCs based on a special TiO2 photoanode with a macropore size of 105 nm exhibited a current density (Jsc) of 20.6 mA cm−2 and a high photo-to-electrical energy conversion efficiency (η) of 9.7%. This high power conversion efficiency is ascribed to the special morphology of the TiO2 photoanode with high dye adsorption due to its ordered and open structures, and also its light scattering and charge collection efficiency.

Continuous Size Tuning of Monodispersed ZnO Nanoparticles and Its Size Effect on the Performance of Perovskite Solar Cells

ZnO has been demonstrated to be a promising candidate to fabricate high efficiency perovskite solar cells (PSCs) in terms of its better electron extraction and transport properties. However, the inability of synthesis of ZnO nanoparticles (NPs) with minimal surface defects and agglomeration remains a great challenge hindering the fabrication of highly efficient PSCs. In this work, highly crystalline and agglomeration-free ZnO NPs with controlled size were synthesized through a facile solvothermal method. Such ZnO NPs were applied in the fabrication of meso-structured PSCs. The solar cells with ∼40 nm ZnO NPs exhibit the highest power conversion efficiency (PCE) of 15.92%. Steady-state and time-resolved photoluminescence measurements revealed the faster injection and lower charge recombination at the interface of ∼40 nm ZnO NPs and perovskite, resulting in significantly enhanced JSC and VOC.

Impact of sol aging on TiO2 compact layer and photovoltaic performance of perovskite solar cell

Perovskite solar cells are known to have a power conversion efficiency dependent on subtle variation in chemical composition and crystal and microstructures of materials, processing conditions, and device fabrication procedures and conditions. The present work demonstrates such strong dependence of power conversion efficiency on a TiO2 film made of the same sol with various aging time. A dense and conformal TiO2 film was prepared by sol-gel method, and the influences of its surface morphology and thickness on performance of perovskite solar cells have been investigated. The surface morphology and thickness of the TiO2 film were tuned by adjusting the aging time of sol, resulting in enhanced short-circuit current density and fill factor of the perovskite solar cells due to increased coverage and roughness of perovskite films, light refraction, and effective charge recombination blocking effect, which were verified by means of the light absorption spectra, photoluminescence of perovskite films with and without hole transport layer, cyclic voltammogram, and electrochemical impedance spectra. The cells with a dense and conformal TiO2 compact layer derived fromthe sol aged for 4 h exhibit a power conversion efficiency of 15.7%, 50% higher than the efficiency based on TiO2 layer derived from 0 h aging sol and 3 times of the efficiency with TiO2 layer made from 8 h aged sol.摘要钙钛矿太阳电池的光伏性能有赖于对材料的化学组分、晶体以及微观结构的精细调控和对工艺条件和制备过程的控制. 本工作针对不同陈化时间的溶胶制备的TiO2致密层与太阳电池性能之间的关联性进行了研究. 研究中, 通过溶胶-凝胶法制备了致密、均匀的TiO2薄膜, 并研究了其表面形貌及厚度对钙钛矿太阳电池性能的影响. 通过调节溶胶的陈化时间可以实现对TiO2表面形貌和厚度的控制, 由于陈化后的溶胶会提高TiO2致密层的覆盖度, 粗糙度及光的折射率, 并有效阻挡电子的复合, 从而导致钙钛矿太阳电池中短路电流密度和填充因子提升. 钙钛矿薄膜的吸收光谱, 光致发光谱, TiO2薄膜的循环伏安测试及整个电池的交流阻抗谱的测试结果, 也进一步论证了该结论. 结果显示使用陈化时间为4 h的溶胶制备的钙钛矿电池获得了15.7%的能量转化效率, 比使用0 h陈化的溶胶制备的太阳电池效率高出50%, 是使用陈化时间为8 h的溶胶制备的太阳能电池效率的3倍.