Synthetic control over orientational degeneracy of spacer cations enhances solar cell efficiency in two-dimensional perovskites

Jun Hu,Andrew M Moran,Jinsong Huang,Wei You,Olivia F Williams,Ninghao Zhou,Masrur Morshed Nahid,Samuel J Stuard,Iain W H Oswald,Zhenkun Guo,Huamin Hu,Yun Lin,Harald Ade,Zhibin Yang,Liang Yan,Xun Xiao,Zheng Chen,James R Neilson

doi:10.1038/s41467-019-08980-x

Abstract

Two-dimensional perovskites have emerged as more intrinsically stable materials for solar cells. Chemical tuning of spacer organic cations has attracted great interest due to their additional functionalities. However, how the chemical nature of the organic cations affects the properties of two-dimensional perovskites and devices is rarely reported. Here we demonstrate that the selection of spacer cations (i.e., selective fluorination of phenethylammonium) affects the film properties of two-dimensional perovskites, leading to different device performance of two-dimensional perovskite solar cells (average n = 4). Structural analysis reveals that different packing arrangements and orientational disorder of the spacer cations result in orientational degeneracy and different formation energies, largely explaining the difference in film properties. This work provides key missing information on how spacer cations exert influence on desirable electronic properties and device performance of two-dimensional perovskites via the weak and cooperative interactions of these cations in the crystal lattice.

Highlights

Two-dimensional perovskites have emerged as more intrinsically stable materials for solar cells
Venkatesan et al have shown that 2D organic–inorganic hybrid perovskites (OIHPs) films exhibit diffraction peaks less than 10 nm−1 because the spacings associated with the low-Q peaks are only possible when the larger cations are present in the system[64]
The oF1PEA 2D OIHP film has an additional peak around Qz = 4.8 nm−1, which can be assigned to n = 3 (Fig. 4b, orange arrow and index)

Summary

Introduction

Two-dimensional perovskites have emerged as more intrinsically stable materials for solar cells. The lead halide-based 2D OIHPs, which have a general formula of (RNH3)2MAn–1PbnX3n+1, have attracted much attention as alternative photovoltaic materials because of their improved stability[24,25,26,27,28,29,30,31,32] These 2D layered perovskites, having the insulating organic cations separating these inorganic slabs, tend to adopt an orientation where these inorganic slabs would be aligned in parallel to the substrate. One would like to replace such aliphatic ammoniums with functional organics, for example, conjugated oligomers that would absorb a complementary portion of the solar spectrum to that of the inorganic framework This improved light absorption could potentially increase the current of 2D OIHP based solar cells and further boost their efficiency. It appears that having a more favorable formation energy and less crystallographic disorder are beneficial for the device performance of these 2D OIHP based solar cells

Methods

Results

Conclusion