Tuning Structure and Performance of 2D/3D Perovskites by Alkyl Chain Length Engineering

Abstract

Bulky 2D alkylammonium cations in metal halide perovskites offer a route to improve both structural stability and optoelectronic performance. This study systematically explores the incorporation of alkylammonium iodides with different chain lengths─dodecylammonium (C12), hexadecylammonium (C16), and octadecylammonium (C18)─into perovskite films for solar cells. Using spectroscopic and nanoscale characterization techniques, we show that C12 provides the best results: enhanced [111] orientation, reduced nonradiative recombination, uniform cation distribution, and improved vertical conductivity. Nanoscale X-ray diffraction and AFM-based infrared spectroscopy revealed that intermediate chain lengths enable favorable lattice expansion and interfacial passivation without hindering crystal growth. Solar cells based on C12-modified films reached power conversion efficiencies over 20%, surpassing both pristine and longer-chain formulations. These findings demonstrate that tuning alkyl chain length is an effective molecular design strategy to guide perovskite crystallization and improve device performance and stability.