Jiajiu Ye

High Consistency Perovskite Solar Cell with a Consecutive Compact and Mesoporous TiO2 Film by One-Step Spin-Coating

Generally, in classic mesoscopic perovskite solar cells (PSCs), the compact blocking layer and mesoporous scaffold layer prepared by two steps or more will inevitably form an interface between them. It is undoubted that the interface contact is not conducive to electron transport and would increase the recombination in the device, resulting in the inferior performance of PSCs. In this work, we constructed a consecutive compact and mesoporous (CCM) TiO2 film to substitute the compact blocking layer and scaffold layer for mesoscopic PSCs. The bottom of the CCM TiO2 film was dense and the top was mesoporous with large uniform macropores. The two parts of the film were consecutive, which could promote the electron transport rate and decrease the charge recombination effectively. Moreover, due to the existence of macropores in the CCM TiO2 film, it was propitious to the deposition of perovskite and charge separation for the perovskite layer. Over 15.0% of average power conversion efficiency (PCE) with high consistency photovoltaic performances was achieved for the CCM TiO2 film based mesoscopic PSCs, which is higher than that with a classic mesoporous structure.

Enhanced performance and stability of perovskite solar cells using NH4I interfacial modifier

Despite organic-inorganic hybrid perovskite solar cells have rapid advances in power conversion efficiency in recent years, the serious instability of the device under practical working conditions is the current main challenge for commercialization. In this study, we have successfully inserted NH4I as an interfacial modifier between the TiO2 electron transport layer and perovskite layer. The result shows that it can significantly improve the quality of the perovskite films and electron extraction efficiency between the perovskite and electron transport layer. The devices with NH4I are obtained an improved power conversion efficiency of 18.31% under AM 1.5G illumination (100 mW cm-2). More importantly, the humidity and UV light stability of the devices are greatly improved after adding NH4I layer. The uncoated devices only decrease by less than 15% of its original efficiency during 700-h stability tests in a humidity chamber (with a relative humidity of 80%) and the efficiency almost maintains 70% of its initial value over 20 h under UV light stress tests. This work provides a potential way by interfacial modification to significantly improve photovoltaic performance and stability of perovskite solar cells.

Highly efficient and stable perovskite solar cell prepared from an in situ pre-wetted PbI2 nano-sheet array film

Due to its good pore-filling and morphology control, a two-step deposition technique has been widely used in perovskite film preparation. However, the initial PbI2 film used for the two-step deposition method is usually dense, crystalline and layered, leading to a poor quality perovskite film with a certain amount of PbI2 residue, thus resulting in an inferior stability and low power conversion efficiency (PCE) of the device. In this work, we developed an in situ pre-wetted PbI2 nano-sheet array film to achieve high-quality CH3NH3PbI3 (MAPbI3) perovskite films via a two-step deposition method. By introducing a small amount of hydrogen chloride isopropanol solution (IPA HCl) into the PbI2 precursor solution, an in situ pre-wetted PbI2 nano-sheet array film was obtained, and then a smooth, continuous, uniform, dense, and PbI2-free perovskite film was formed through a reaction with CH3NH3I. After optimization, the device prepared using the in situ pre-wetted PbI2 nano-sheet array film achieved a promising PCE of 19.19%. Moreover, it also had good reproducibility and long term stability, as the devices based on the in situ pre-wetted PbI2 nano-sheet array film retained over 80% of the initial PCE after exposing to ambient air for two months.

Influence of Structure and Morphology of Perovskite Films on the Performance of Perovskite Solar Cells

Perovskite solar cells based on the inorganic/organic hybrid perovskite have attracted increasing attention over the past 3 years. Many studies have been done in this area. Controling the morphology of the perovskite film is an effective way to improve the photoelectric conversion efficiency of the devices. In our reserch, we studied the influence of structure and morphology of perovskite films on the performance of the organic-inorganic hybrid perovskite solar cells which prepared by a sequential deposition method. Mesoporous TiO2 scaffold were introduced as electron collecting layer. Lead iodide (PbI2) was then spin cast on the TiO2 scaffold. The PbI2 subsequently transformed into the perovskite (CH3NH3PbI3) by dipping the TiO2/PbI2 film into a solution of CH3NH3I. We studied the difference between the PbI2 film with or without drying under room temperature after spin-coating. Through drying under room temperature, larger pores formed in the PbI2 film. While without drying under room temperature, smaller and shallower pores formed in the PbI2 film. The results show that larger pores in PbI2 film leads to more complete transformation of PbI2 to CH3NH3PbI3 and larger CH3NH3PbI3 particles. CH3NH3PbI3 films were prepared with three different processes: (a) direct dipping the PbI2 film with smaller pores into the CH3NH3I solution; (b) direct dipping the PbI2 with larger pores into the CH3NH3I solution; (c) dipping the PbI2 with larger pores into the CH3NH3I solution after pre-wetting.The resulting CH3NH3PbI3 films were studied with SEM, UV-vis absorption spectrum and XRD. The particles size of the CH3NH3PbI3 are 150, 250 and 350 nm for process (a), (b) and (c) respectively. CH3NH3PbI3 films fabricated through process (a) show insufficient absorption due to the insufficient transformation of the PbI2. The pre-wetting procedure leads to slower reaction result in larger CH3NH3PbI3 particle size. Devices with proper size of CH3NH3PbI3 particles show the highest photoelectric conversion efficiency. An efficiency of 13.5% was achieved with a Jsc of 17.8 mA/cm, a Voc of 1.05 V and a FF of 72.5%.