Molecular doping enabled scalable blading of efficient hole-transport-layer-free perovskite solar cells

Abstract

The efficiencies of perovskite solar cells (PSCs) are now reaching such consistently high levels that scalable manufacturing at low cost is becoming critical. However, this remains challenging due to the expensive hole-transporting materials usually employed, and difficulties associated with the scalable deposition of other functional layers. By simplifying the device architecture, hole-transport-layer-free PSCs with improved photovoltaic performance are fabricated via a scalable doctor-blading process. Molecular doping of halide perovskite films improved the conductivity of the films and their electronic contact with the conductive substrate, resulting in a reduced series resistance. It facilitates the extraction of photoexcited holes from perovskite directly to the conductive substrate. The bladed hole-transport-layer-free PSCs showed a stabilized power conversion efficiency above 20.0%. This work represents a significant step towards the scalable, cost-effective manufacturing of PSCs with both high performance and simple fabrication processes.

Fig. 1

Doctor blading and doping of perovskite films by F4TCNQ. a Schematic illustration of a doctor-bladed perovskite film and the chemical structure of F4TCNQ dopant. b Cross-sectional SEM image of the MAPbI₃ film deposited directly onto ITO glass via bladed coating at 150 °C, showing the film thickness of around 500 nm. Topography KPFM images of c, f MAPbI₃, d, g F4TCNQ-doped MAPbI₃, and e, h F4TCNQ solid-diffused MAPbI₃ films. CPD represents the contact potential difference between the tip and sample’s surface. i Surface potential profiles of different perovskite films as indicated. j Schematic illustration of the energy diagram and electron transfer process for MAPbI₃:F4TCNQ blends

Fig. 2

Conductivities and photoluminescence lifetimes of neat or doped perovskite films. a Geometry for the lateral conductivity measurement: the perovskite films were 500 nm thick, with 1 mm gold (Au) electrodes separated by 100 μm. b J–V curves of neat or F4TCNQ-doped MAPbI₃ deposited on normal glass substrates, where the current was measured along the lateral direction. c TRPL decay curves of glass/MAPbI₃ and glass/MAPbI₃:F4TCNQ. PL lifetimes were calculated by single exponential fitting. d c-AFM setup. Topographic AFM images of e MAPbI₃ and g MAPbI₃:F4TCNQ films, with locations where the c-AFM tip measured the grain and GB currents. Local dark currents measured at the GBs and on the grains for the f MAPbI₃ film and h MAPbI₃:F4TCNQ film

Fig. 3

Perovskite film morphology, device structure, and photovoltaic performance. a Low magnification and b high magnification SEM images of bladed and doped MAPbI₃ film prepared with MHP (0.225 wt%) and MACl (0.5 wt%) as additive, followed by co-solvents annealing treatment. c Schematic illustration of the HTL-free device configuration. d J–V characteristics, e Steady-state current and stabilized PCE measured at a maximum power point (0.93 V), f EQE and integrated current density, and g PCE histogram of PSCs based on MAPbI₃:F4TCNQ films (with 0.03 wt% F4TCNQ)

Fig. 4

Interfacial hole transfer dynamics. Schematic illustrations of hole transfer at the a ITO/MAPbI₃ or b ITO/F4TCNQ-doped MAPbI₃ interface