Enhancement of 3D/2D Perovskite Solar Cells Using an F4TCNQ Molecular Additive
Jingsong Sun, Naresh Chandrasekaran, Chang Liu, Andrew D. Scully, Wenping Yin, Chun Kiu Ng, Jacek J. Jasieniak
Abstract
Recent developments in hybrid organic-inorganic lead halide perovskite solar cells (PSCs) have shown that use of a 2-dimensional (2D) perovskite capping layer on a 3D perovskite absorber layer (3D/2D PSCs) results in substantially improved environmental stability of the devices. However, in these 3D/2D PSC structures the poor charge transporting properties through the 2D layer hinder device performance, particularly for thicker 2D layers. Here, we report a facile method that overcomes some of the inherent challenges in using such 2D capping layers through the introduction of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) as a molecular additive into the 2D layer. It is found that this additive undergoes partial charge transfer with the perovskite layer to provide a passivation effect, which also modifies the crystalline domain sizes of the 2D perovskite. PSCs incorporating a F4TCNQ-modified 2D capping layer grown in situ on top of the 3D Cs/MA/FA mixed-cation perovskite absorber layer display modified interfacial characteristics that yield improved charge extraction and reduced charge recombination compared with 3D/2D PSCs comprising an unmodified 2D capping layer. This modification results in 3D/2D PSCs for which the maximum power conversion efficiency is increased to more than 20% compared with 18.2% for unmodified 2D capping layers.