Highly efficient and thermal stable guanidinium-based two-dimensional perovskite solar cells via partial substitution with hydrophobic ammonium

Layered two-dimensional (2D) perovskite solar cells (PVSCs) with a chemical formula of C(NH2)(3)(CH3NH3)(3)Pb3I10 (n=3) have been fabricated through additive engineering, wherein stoichiometrically equivalent guanidinium (GA(+)) and methylammonium (MA(+)) serve as spacer cations. The crystallinity of the perovskite films is dramatically enhanced with proper amount of methylammonium thiocyanate (MASCN) added into the precursor solution. In addition, we substitute a small amount of MA(+) with hydrophobic phenylethylammonium (PEA(+)), which can passivate trap states of the perovskite films. As a result, the open circuit voltage increases to 1.1 V and the best power conversion efficiency (PCE) of 10.12% is yielded. Furthermore, superior thermal stability and balanced moisture stability of the PEA-substituted GA-based PVSCs are demonstrated, compared to the popular 3D MAPbI(3) and 2D PEA-based PVSCs. They retain approximately 80% of the original PCE after 30 d at 20% relative humidity (RH), and 50% of the original PCE after 3200 min at 85 degrees C without any encapsulation. This work suggests a new route to achieve both heat and humidity stable PVSCs by simply mixing different spacer cations.