Stable Hole-Transporting Material-Free Perovskite Solar Cells with Efficiency Exceeding 14% via the Introduction of a Malonic Acid Additive for a Perovskite Precursor

Hole transport material-free perovskite solar cells (HF-PSCs) offer low-cost photovoltaic devices. For development and commercialization, they are more attractive than the expensive HTL-contained perovskite solar cells. Herein, we focused on enhancing the stability and efficiency of HF-PSCs with the malonic acid (MA) addition to the methylammonium lead iodide. The introduced additive increases the perovskite crystallinity and assembles a perovskite layer with larger grains along with fewer surface defects. In addition, the MA-modified HF-PSCs show suppressed charge recombination within devices, and a lower charge trap density has been obtained for them. A considerable power conversion efficiency of 14.14% is achieved for MA-modified HF-PSCs, higher than the performance of 11.88% for the untreated HF-PSCs. Finally, MA-based HF-PSCs show higher shelf stability than the control HF-PSCs. It is because the MA-modified perovskite layer with passivated grain boundaries is better at repelling water.