A tailored spacer molecule in 2D/3D heterojunction for ultralow-voltage-loss and stable perovskite solar cells

Abstract

2D/3D heterojunction engineering has been regarded as a feasible method to improve the photovoltaic performance of perovskite solar cells (PSCs). A spacer molecule poses a huge influence on the structural and optoelectronic properties of 2D perovskites. A specific functional group embedded spacer molecule is highly expected to build an effective 2D capping layer for efficient, stable, and hysteresis-free PSCs. Here, a tailored spacer molecule, 4-hydroxy-phenylethylamine iodide (OH-PEAI), is developed for high-performance 2D/3D PSCs. A combined theoretical and experimental study suggests that OH-PEAI based 2D structure on the 3D surface significantly reduces defect density and mitigates nonradiative recombination. The target PSCs deliver an efficiency of 21.38% compared to 19.54% for the control device. A high open-circuit voltage (V_oc) up to 1.234 V can be achieved with a V_oc loss of only 0.376 V and the hysteresis can be totally eliminated. 2D/3D PSCs using a low-bandgap 3D perovskite can yield a high efficiency of 23.28%. The 2D layer also provides a robust interface that protects vulnerable 3D perovskite films from moisture attacks. As a result, the unencapsulated 2D/3D PSCs show excellent long-term stability retaining 93% of initial PCE in ambient air at 30% relative humidity for 480 h.