Improving the Efficiency of Hole-Conductor-Free Carbon-Based Planar Perovskite Solar Cells with Long-Term Stability by Using the Hydrazine Acetate Additive via the One-Step Method

Hole transport material (HTM)-free carbon-based perovskite solar cells (C-PSCs) have attracted much attention due to their low cost and high stability since first reported in 2013. However, the efficiency issues still need to be addressed to increase the commercial competitiveness. Here we make the HTM-free C-PSCs with a simple and low-cost planar-heterojunction structure, comprising compact SnO2, simple equimolar CH3NH3I + PbI2 perovskite precursors, and commercial carbon paste, by the one-step solution method. During the preparation process, only the perovskite layer needs to be prepared in the glovebox, while other functional layers are completed in the air. The performance of the device can be greatly improved by introducing hydrazine acetate as the additive in the perovskite precursor solution. With the optimal ratio, the C-PSCs achieve an average power conversion efficiency (PCE) of 10.91 ± 0.3%, and the champion device shows a satisfying PCE of 11.30%, which increases remarkably by as much as 106% compared with the pristine control device. All the C-PSCs retain 100% of the initial performance after storage under ambient conditions without encapsulation for more than 120 days.