Highly stable hole-conductor-free perovskite solar cells based upon ammonium chloride and a carbon electrode

Organic-inorganic hybrid perovskite solar cells (PSCs) have become a research hotspot due to the impressive photovoltaic performance. The perovskite film plays an extremely important role in the light-to-electricity conversion, meanwhile, the stability of PSCs is also an important factor affecting the application of devices. Here we demonstrate a kind of stable PSCs by using simple solution-process in an air enviroment with about 45% relative humidity. Firstly, the NH₄Cl was added to the perovskite precursor solution to adjust the kinetics of crystallization and growth of active layer, and then obtain high-quality CH₃NH₃PbI₃ perovskite films. Hydrophobic carbon electrode was used to protect the perovskite active layers and further improve the stability of PSCs, which optimized the structure of the devices at the same time. We adjusted the amount of NH₄Cl in the perovskite precursor solution (PbI₂: CH₃NH₃I: NH₄Cl = 1: 1: x (x = 0 ∼ 1), and investigated the effect of that on the properties of perovskite active layers and PSCs. The above results showed that the devices achieved fully covered perovskite thin films and improved the photovoltaic performance of PSCs when the NH₄Cl additive was x  = 0.8. The short-circuit current density (J_sc), fill factor (FF) and power conversion efficiency (PCE) were significantly enhenced. Under the condition of ambient air and no encapsulation, the PSCs exhibited good stability after 576 h test, and the PCE was still about 96% of the initial efficiency.