The Zn/Sn ratio in Cu₂ZnSn(S, Se)₄ (CZTSSe) films has been regulated to control the composition-related phase, defect, and photoelectric properties for high performance kesterite solar cells. It is found that the increase in the Zn/Sn ratio can slightly narrow the energy band gap to extend the light absorption range and improve the photocurrent. Optimal Zn/Sn ratio of 1.39 in CZTSSe film is obtained with the least secondary phase, the lowest defect density, and the longest charge recombination lifetime. Up to 10.1% photoelectric conversion efficiency has been achieved by this composition regulation.

TiO₂ nanorods have been prepared on ITO substrates by dc reactive magnetron sputtering technique. The hydroxyl groups have been introduced on the nanorods surface. The structure and the optical properties of these nanorods have been studied. The dye-sensitized solar cells (DSSCs) have been assembled using these TiO₂ nanorods as photoelectrode. And the effect of the hydroxyl groups on the properties of the photoelectric conversion of the DSSCs has been studied.

Depleted bulk heterojunction (DBH) PbS quantum dot solar cells (QDSCs), appearing with boosted short-circuit current density (J_sc), represent the great potential of solar radiation utilization, but suffer from the problem of increased interfacial charge recombination and reduced open-circuit voltage (V_oc). Herein, we report that an insertion of ultrathin Al₂O₃ layer (ca. 1.2 Å thickness) at the interface of ZnO nanowires (NWs) and PbS quantum dots (QDs) could remarkably improve the performance of DBH-QDSCs fabricated from them, i.e., an increase of V_oc from 449 mV to 572 mV, J_sc from 21.90 mA/cm² to 23.98 mA/cm², and power conversion efficiency (PCE) from 4.29% to 6.11%. Such an improvement of device performance is ascribed to the significant reduction of the interfacial charge recombination rate, as evidenced by the light intensity dependence on J_sc and V_oc, the prolonged electron lifetime, the lowered trap density, and the enlarged recombination activation energy. The present research therefore provides an effective interfacial engineering means to improving the overall performance of DBH-QDSCs, which might also be effective to other types of optoelectronic devices with large interface area.

The rutile TiO₂ nanorod arrays with 240 nm in length, 30 nm in diameter, and 420 μm^-2 in areal density were prepared by the hydrothermal method to replace the typical 200-300 nm thick mesoporous TiO₂ thin films in perovskite solar cells. The CH₃NH₃PbI_3-xBr_x capping layers with different thicknesses were obtained on the TiO₂ nanorod arrays using different concentration PbI₂· DMSO complex precursor solutions in DMF and the photovoltaic performances of the corresponding solar cells were compared. The perovskite solar cells based on 240 nm long TiO₂ nanorod arrays and 420 nm thick CH₃NH₃PbI_3-xBr_x capping layers showed the best photoelectric conversion efficiency (PCE) of 15.56% and the average PCE of 14.93±0.63% at the relative humidity of 50%-54% under the illumination of simulated AM 1.5 sunlight (100 mW· cm^-2).

A star hybrid inorganic-organic perovskite material selected as an outstanding absorbing layer in solar cells benefits from multiple preparation techniques and excellent photoelectric characteristics. Among numerous synthetic processes, uniform, compact, and multi-stack perovskite thin films can be manufactured using vacuum deposition. During sequential vacuum deposition, the penetration ability of the organic molecules cannot be effectively controlled. In addition, the relationship between the thickness of the inorganic seeding layer and the organic molecule concentration for optimized devices using an evaporation-solution method is unclear. In this work, we prepared high-quality perovskite films by effectively controlling the penetration ability and chemical quantity of organic methyl ammonium iodide by monitoring the evaporation pressure and time. Thus, a device efficiency of over 15% was achieved with an all-vacuum prepared perovskite film. For the evaporation-solution method, we reacted different thicknesses of inorganic lead iodine with various concentrations of the organic molecule solution. The inorganic layer thickness and organic molecule concentration showed a linear relationship to achieve an optimum perovskite film, and an empirical formula was obtained. This work noted the key parameters of two intercalation reactions to prepare perovskite films, which paves a way to deliver a device that enables multi-layered structures, such as tandem solar cells.

A new hybrid organic-inorganic structure of FTO/TiO₂/Se/HTL/Au based selenium solar cell has been fabricated through a low-cost spin-coating process in air. In this process, selenium is completely dissolved in hydrazine, to form a homogeneous precursor solution. After spin-coating the precursor solution on the TiO₂ substrates, following by sintering at 200℃ for 5min, a uniform selenium film with crystalline grains is formed. The selenium based solar cell exhibits an efficiency of 1.23% under AM1.5 illumination (100 mW·cm^-2), short-circuit current density of 8 mA·cm^-2, open-circuit voltage of 0.55 V, and fill factor of 0.37. Moreover, the device shows a stable ability with almost the same performance after 60 days.

A depth behavioral understanding for each layer in perovskite solar cells (PSCs) and their interfacial interactions as a whole has been emerged for further enhancement in power conversion efficiency (PCE). Herein, NiO@Carbon was not only simulated as a hole transport layer but also as a counter electrode at the same time in the planar heterojunction based PSCs with the program wxAMPS (analysis of microelectronic and photonic structures)-1D. Simulation results revealed a high dependence of PCE on the effect of band offset between hole transport material (HTM) and perovskite layers. Meanwhile, the valence band offset (Δ E_v) of NiO-HTM was optimized to be -0.1 to -0.3 eV lower than that of the perovskite layer. Additionally, a barrier cliff was identified to significantly influence the hole extraction at the HTM/absorber interface. Conversely, the Δ E_v between the active material and NiO@Carbon-HTM was derived to be -0.15 to 0.15 eV with an enhanced efficiency from 15% to 16%.

The fabrication of high-quality electron-selective layers at low temperature is a prerequisite to realizing efficient flexible and tandem perovskite solar cells (PSCs). A colloidal-quantum-dot ink that contains TiO₂ nanocrystals enables the deposition of a flat film with matched energy level for PSCs; however, the selection of ligands on the TiO₂ surface is still unexplored. Here, we systematically studied the effect of the titanium diisopropoxide bis(acetylacetonate) (TiAc₂) ligand on the performance of PSCs with a planar n-i-p architecture. We prepared TiO₂ nanocrystals from TiCl₄ and ethyl alcohol with Cl^- ligands attached on its surface and we found that a tiny amount of TiAc₂ treatment of as-prepared TiO₂ nanocrystals in a mixed solution of chloroform and methyl alcohol can enhance PSC power conversion efficiency (PCE) from 14.7% to 18.3%. To investigate the effect of TiAc₂ ligand on PSCs, TiO₂ samples with different TiAc₂ content were prepared by adding TiAc₂ into the as-obtained TiO₂ nanocrystal solution. We use x-ray photoelectron spectroscopy to identify the content of Cl so as to reveal that Cl ligands can be substituted by TiAc₂. We speculate that the improvement in PCE originates from amorphous TiO₂ formation on the TiO₂ nanocrystal surface, whereby a single-molecule layer of amorphous TiO₂ facilitates charge transfer between the perovskite film and the TiO₂ electronic transport layer, but excessive TiAc₂ lowers the PSC performance dramatically. We further prove our hypothesis by x-ray diffraction measurements. We believe the PCE of PSCs can be further improved by carefully choosing the type and changing the content of surface ligands on TiO₂ nanocrystal.

The kesterite Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells have yielded a prospective conversion efficiency among all thin-film photovoltaic technology. However, its further development is still hindered by the lower open-circuit voltage (V_oc), and the non-ideal bandgap of the absorber is an important factor affecting this issue. The substitution of Sn with Ge provides a unique ability to engineer the bandgap of the absorber film. Herein, a simple precursor solution approach was successfully developed to fabricate Cu₂Zn(Sn_yGe_1-y)(S_xSe_1-x)₄ (CZTGSSe) solar cells. By precisely adjusting the Ge content in a small range, the V_oc and J_sc are enhanced simultaneously. Benefitting from the optimized bandgap and the maintained spike structure and light absorption, the 10% Ge/(Ge+Sn) content device with a bandgap of approximately 1.1 eV yields the highest efficiency of 9.36%. This further indicates that a precisely controlled Ge content could further improve the cell performance for efficient CZTGSSe solar cells.

Perovskite solar cells with planar structure are attractive for their simplified device structure and reduced hysteresis effect. Compared to conventional mesoporous devices, TiO₂ porous scaffold layers are removed in planar devices. Then, compact TiO₂ electron transport layers take the functions of extracting electrons, transporting electrons, and blocking holes. Therefore, the properties of these compact TiO₂ layers are important for the performance of solar cells. In this work, we develop a mixed spray pyrolysis method for producing compact TiO₂ layers by incorporating TiO₂ nanoparticles with different size into the precursor solutions. For the optimized nanoparticle size of 60 nm, a power conversion efficiency of 16.7% is achieved, which is obviously higher than that of devices without incorporated nanoparticles (9.9%). Further investigation reveals that the incorporation of nanoparticles can remarkably improve the charge extraction and recombination processes.

The performance of dye-sensitized solar cells (DSSCs) is strongly affected by the properties of semiconductor nanoparticles. In this work, we used TiO₂ particles prepared by TiCl₄ hydrolysis n times on Al₂O₃ films (A/T(n)), and investigated morphology, photoelectric, and electron transport properties of A/T(n). The TiO₂ shell was composed of 10-20 nm nanoparticles and the number of nanoparticles increased with increasing TiCl₄ treatment times. The highest photoelectric conversion efficiency of 3.23% was obtained as A/T(4). IMPS results indicated that electron transport rate was high enough to conduct current, and was not the dominating effect to limit the J_sc. J_sc was mainly determined by dye loading on TiO₂ and the interconnection of TiO₂. These may provide a new strategy for preparing semiconductor working electrodes for DSSC.