Xuguang Jia

Totally room-temperature solution-processing method for fabricating flexible perovskite solar cells using an Nb2O5–TiO2 electron transport layer

Flexible perovskite solar cells are new technology-based products developed by the global solar industry and are promising candidates for realizing a flexible and lightweight energy supply system for wearable and portable electronic devices. A critical issue for flexible perovskite solar cells is to achieve high power conversion efficiency (PCE) while using low-temperature solution-based technology for the fabrication of a compact charge collection layer. Herein, we innovatively introduce niobium ethoxide as a precursor additive to TiO2 NCs, which allows realization of an Nb2O5–TiO2 electron transport layer (ETL). The presence of Nb2O5 remarkably enhances electron mobility and electrical conductivity of the ETLs. In addition, uniform perovskite films are prepared by an annealing-free solution-based method. The excellent performance of the cell is attributed to its smooth film surface and high electron mobility, and performance is verified by the effective suppressions of charge recombination and time-resolved photoluminescence. PCEs of 15.25% and 13.60% were obtained for rigid substrates (glass/fluorine-doped tin oxide) and an indium tin oxide/PET (poly(ethylene terephthalate)) flexible substrate by using a totally room-temperature solution-processing method, respectively.

High-Performance Flexible Perovskite Solar Cells from Low-temperature Solution Processing Using Combined Effect of Anion and Cation for Effective Interfacial Optimization

Exploration of low-temperature solution-processing methodologies for fabricating planar perovskite solar cells (PSCs) is important for industrial mass production and helps simplify the manufacture and design of flexible perovskite solar cells. However, the interface between electron-transport layers (ETLs) and perovskite layers is crucial for the development of highly efficient flexible PSCs. We report a drastically improved solar cell efficiency through surface optimization of TiO2 ETLs by using a simple and inexpensive ionic compound that shows high optical transparency and superior electron mobility. Solution-derived TiO2 nanocrystalline films are employed at low temperatures as ETLs through solution processing. The modification of TiO2 with NH4 Cl can increase the interactions between the surface and organic-inorganic hybrid perovskites; Cl anions lead to a stronger interfacial coupling between TiO2 and perovskite. Ammonium cations tend to combine with perovskite. Due to this strong combined effect of the ionic compound, the efficiency of PSC from low-temperature solution processing reaches 18.71 % on rigid glass/indium tin oxide (ITO) for an improvement of 12.6 % over a control device using bare TiO2 . Furthermore, the power conversion efficiency (PCE) can reach an efficiency of 17.69 % for the ITO/PEN substrates. This work contributes to the evolution of flexible PSCs with simple fabrication and high device performance.

Observation of enhanced hot phonon bottleneck effect in 2D perovskites

We thoroughly investigated the carrier-phonon relaxation process in 2D halide perovskites with the general formula of (BA)2(MA)n-1PbnI3n+1, where n = 2, 3, and 4, by femtosecond transient absorption spectroscopy. A significant enhancement of the hot phonon bottleneck effect is observed in the natural multiple quantum well with n = 2 and 3. Specifically, the sample with n = 3 shows a 1000 ps hot carrier relaxation time to reach room temperature, which is 10 times longer compared with its three-dimensional counterpart. We believe that both the organic cation and quantum confinement effect are responsible for this phenomenon. The acoustic phonon cannot propagate due to the decrease in group velocity caused by the confinement effect in such a quantum well structure. In addition, the confined acoustic phonons can up-convert to optical phonons due to the presence of a “hybrid phonon” induced by the organic cation. This result suggests a promising way to obtain long-live hot carrier materials.

Theoretical and experimental study on the optical and electrical properties of Cu2ZnTiS4 and its photovoltaic applications

In this paper, a I2-II-IV-VI4 quaternary kesterite-structured semiconductor Cu2ZnTiS4 thin film is synthesized by a co-sputtering approach. Its structural properties are investigated via various experimental techniques combining the prediction from first-principle calculations. Stable chemical potential range is analyzed according to the formation energy of Cu2ZnTiS4 and its competing phases. The results show that the stable pure Cu2ZnTiS4 phase can exist and the most possible impure phases are ZnS and Cu2TiS3. X-ray diffraction analysis reveals the cubic crystal structure, which is expected in the calculations. Raman spectrum analysis excludes the possibility of ZnS and Cu2TiS3 phases, which corroborates the formation of single Cu2ZnTiS4 phase. The Cu2ZnTiS4 thin film exhibits dense and pinhole free surface morphologies and a bandgap of 1.42 eV is observed. The initial photovoltaic device based on this material exhibits a 0.83% efficiency. These findings offer a promising candidate material for quaternar...