Enhancing the thermal stability of the carbon-based perovskite solar cells by using a Cs x FA 1- x PbBr x I 3- 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 CH 3 NH 3 PbI 3 as a perovskite and organic hole-transport material (HTM) remains a challenge. In this study, we employed the thermally stable (NH 2 ) 2 CHPbI 3 (FAPbI 3 ) 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 PbI 2 , we obtained a phase-stable Cs x FA 1- x PbBr x I 3- 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.