Yang Huang

Mesoporous SnO2 nanoparticle films as electron-transporting material in perovskite solar cells

Perovskite solar cells with mesoporous metal oxide films as scaffold layers have demonstrated very impressive advances in performance recently. Here, we present an investigation into mesoporous perovskite solar cells incorporating mesoporous SnO2 nanoparticle films as electron-transporting materials and scaffold layers, to replace traditional mesoporous TiO2 films. We have optimized the SnO2 film thickness and treated the surface of the SnO2 film with an aqueous solution of TiCl4. Due to the TiCl4 treatment the recombination process was significantly retarded. The short-circuit current density (Jsc) and open-circuit voltage (Voc) reached nearly 18 mA cm−2 and 1 V, respectively. Consequently, the power conversion efficiency of the device with the SnO2 film exceeded 10%.

Inside-out Ostwald ripening: A facile process towards synthesizing anatase TiO2 microspheres for high-efficiency dye-sensitized solar cells

A facile inside-out Ostwald ripening route to the morphology-controlled preparation of TiO2 microspheres is developed. Here, TiO2 hollow microspheres (HM) and solid microspheres (SM) are prepared by adjusting the volume ratio of isopropanol (IPA) to acetylacetone (Acac) in the solvothermal process. During the formation process of HM, precipitation of solid cores, subsequent deposition of outer shells on the surface of cores, and simultaneous core dissolution and shell recrystallization are observed, which validate the inside-out Ostwald ripening mechanism. Design and optimization of the properties (pore size, surface area, and trap state) of TiO2 microspheres are vital to the high performance of dyesensitized solar cells (DSSCs). The optimized TiO2 microspheres (rHM and rSM) obtained by post-processing on recrystallization, possess large pore sizes, high surface areas and reduced trap states (Ti3+ and oxygen vacancy), and are thus ideal materials for photovoltaic devices. The power conversion efficiency of DSSCs fabricated using rHM photoanode is 11.22%, which is significantly improved compared with the 10.54% efficiency of the rSM-based DSSC. Our work provides a strategy for synthesizing TiO2 microspheres that simultaneously accommodate different physical properties, in terms of surface area, crystallinity, morphology, and mesoporosity.

New insight into solvent engineering technology from evolution of intermediates via one-step spin-coating approach

The anti-polar solvent technique is an effective way to improve the film quality in a perovskite solar cell. In this work, we reveal the reason why chlorobenzene (CBZ) plays an important role in controlling the crystallization process. By investigating the formation of intermediate phases in the precursor solution, we observed that the CH3NH3I (MAI)-PbI2-dimethylformamide (DMF) or MAI-PbI2-dimethylsulphoxide (DMSO) adducts have not yet formed until washed with non-polar solvent. The accelerated formation of intermediate phase yields high crystalline perovskite layers. Rapid solvent evaporation and retarded perovskite crystallization in one-step method are efficient to obtain high-quality perovskite films. Consequently, MAI-PbI2-DMSO intermediate shows neat rod-like structure with high crystallinity, which eventually transforms extremely dense and uniform perovskite films.摘要反溶剂技术可以有效改善钙钛矿薄膜的质量. 本文揭示了氯苯(CBZ) 在结晶过程中起的重要作用. 通过研究前体溶液中配合物的结 构变化, 我们观察到, 在滴加反溶剂之前, MAI-PbI2-DMF或MAI-PbI2-DMSO尚未形成. 快速去除多余溶剂后形成中间相, 延缓钙钛矿结晶是 得到高质量钙钛矿薄膜的关键. 其中MAI-PbI2-DMSO中间体表现出了高结晶的棒状结构, 因此最终转变成非常致密和均匀的钙钛矿薄膜.

Identification and characterization of a new intermediate to obtain high quality perovskite films with hydrogen halides as additives

High quality perovskite films were fabricated from different precursor solutions containing a certain proportion of different hydrogen halides. An anti-solvent, toluene, was used here to isolate an intermediate from the perovskite precursor solution to reveal the impact of the hydrogen halides on the crystallization of perovskite films. From the Fourier transform infrared spectra we found that the stretch vibration of CO for pure N,N-dimethylformamide (DMF) appeared at 1663 cm−1, which was shifted to a smaller wavenumber while reacting DMF with CH3NH3I (MAI) + PbI2 and MAI + PbI2 + HX (X = Cl, Br, I). Moreover, the appearance of X-ray diffraction (XRD) peaks at low angles (near 8 degrees) as well as some small angle shift showed that the MAI–PbI2–DMF–xHX (X = Cl, Br, I) intermediate was formed, which benefits perovskite crystallization because the formation of the intermediate will avoid a rapid reaction between MAI and PbI2. Whats more, the solubility of the precursor can be improved by adding hydrogen halides. By adding a certain amount of hydrogen halide into the one-step perovskite precursor solution we can obtain pin-hole free and almost no defect films. Transient absorption (TA) was carried out to investigate the charge recombination in intrinsic perovskite films and perovskite devices, giving some reasonable interpretations.

Promoting perovskite crystal growth to achieve highly efficient and stable solar cells by introducing acetamide as an additive

To date, perovskite solar cells (PSCs) have achieved superior photovoltaic performance with a high power conversion efficiency (PCE) of over 22%. However, there are very few devices which have a high PCE and high stability simultaneously. In this study, we fabricated PSCs made from (FAPbI3)0.85(MAPbBr3)0.15 using the non-volatile Lewis base acetamide (CH3CONH2) as an additive. Compared to a reference device, the device containing 5xa0mg mL−1 CH3CONH2 displayed a markedly improved PCE of 19.01% and less hysteresis, due to its high-quality film with a better crystal structure, evidently larger grain size and greater thickness. In addition, the device with CH3CONH2 exhibited better humidity and heat stability. The unsealed device could maintain about 70% and 50% of its starting PCE under around 50% and 80% relative humidity (RH) for 1000 h and 700 h, respectively. Meanwhile, the unsealed device with CH3CONH2 could retain about 80% and 60% of its starting PCE at 60 °C and 85 °C for 200 h and 150 h, respectively. These results clearly show that using CH3CONH2 as an additive can promote crystal growth and enhance the grain size of perovskite thin films and introducing a suitable additive can realize the simultaneous improvement of the PCE and stability of PSCs.