A pressure-assisted annealing method for high quality CsPbBr3 film deposited by sequential thermal evaporation.

All-inorganic CsPbBr3 perovskite solar cells have triggered incredible interest owing to their superior stability, especially under high temperature conditions. Different from the organic-inorganic hybrid perovskites, inorganic CsPbBr3 perovskite always need a high annealing temperature for the formation of a cubic phase. Generally, the higher temperature (over 300 °C) and longer annealing time will promote the growth of CsPbBr3, resulting in larger grain sizes and lower trap density in the crystals. However, CsPbBr3 perovskite can also be damaged by excessive annealing temperature (∼350 °C) and time, since PbBr2 only has a melting temperature close to 357 °C. To address this issue, herein, we developed a novel pressure-assisted annealing method to prevent the sublimation of PbBr2 at high temperature. The CsPbBr3 films were firstly deposited by sequential thermal evaporation, and then annealed at 335 °C in an alloy pressure vessel. By controlling the pressure of the vessel, we obtained CsPbBr3 films with various morphologies. At normal atmospheric pressure, the as-prepared CsPbBr3 film exhibited small grain sizes and was full of pinholes. With the increase of annealing pressure, the grain sizes of the film showed a significant increasing trend, and the pinholes gradually vanished. When the pressure value came to 10 MPa, compact and uniform CsPbBr3 films with large grain sizes were obtained. Based on these films, CsPbBr3 perovskite solar cells with FTO/compact-TiO2/CsPbBr3/carbon architecture achieved a champion power conversion efficiency of 7.22%.

Enhancing the thermal stability of the carbon-based perovskite solar cells by using a Cs x FA1-x PbBr x I3-x light absorber.

Despite the impressive photovoltaic performance with a power conversion efficiency beyond 23%, perovskite solar cells (PSCs) suffer from poor long-term stability, failing by far the market requirements. Although many efforts have been made towards improving the stability of PSCs, the thermal stability of PSCs with CH3NH3PbI3 as a perovskite and organic hole-transport material (HTM) remains a challenge. In this study, we employed the thermally stable (NH2)2CHPbI3 (FAPbI3) as the light absorber for the carbon-based and HTM-free PSCs, which can be fabricated by screen printing. By introducing a certain amount of CsBr (10%) into PbI2, we obtained a phase-stable Cs x FA1-x PbBr x I3-x perovskite by a "two-step" method and improved the device power conversion efficiency from 10.81% to 14.14%. Moreover, the as-prepared PSCs with mixed-cation perovskite showed an excellent long-term stability under constant heat (85 °C) and thermal cycling (-30 °C to 85 °C) conditions. These thermally stable and fully-printable PSCs would be of great significance for the development of low-cost photovoltaics.

Improving the intrinsic thermal stability of the MAPbI3 perovskite by incorporating cesium 5-aminovaleric acetate.

Cesium 5-aminovaleric acetate (NH2C4H8COOCs) was used to improve the intrinsic thermal stability of the methylammonium lead triiodide (MAPbI3) perovskite. The corresponding carbon-based perovskite solar cells without encapsulation showed favourable stability at 100 °C for 500 h.