Brown University Chem: Highly efficient and stable perovskite solar cells based on continuous grain boundary functionalization

At present, the photoelectric conversion efficiency of organic-inorganic hybrid perovskite solar cells has reached 22.7%, surpassing the commercial crystalline silicon solar cells. However, because perovskite materials are difficult to stabilize in the atmosphere for a long time, they are still the Achilles heel that limits their industrialization. The defects of perovskite polycrystalline film are mostly present in the surface of the film and the grain boundary between adjacent grains. Carrier recombination and material degradation are active in these areas, which seriously restricts the stability and efficiency of the device. At present, many methods of surface passivation are used to isolate the material from contact with water and oxygen. However, the surface passivation materials currently reported are mostly high molecular polymers, and the choice of these polymers is often random. The random polymer is doped into the perovskite film, hindering the transport of carriers, thereby partially sacrificing the excellent optoelectronic properties of the material.

[Introduction]

Recently, Chem published an article entitled "Co ntinuous Grain-Boundary Functio nalization for High-Efficiency Perovskite Solar Cells with Exceptional Stability". The authors of the article are Prof. Nitin. P. Padture and Prof. Yuanyuan Zhou from Brown University in the United States and Prof. Shu Shuping from Qingdao Institute of Bioenergy and Process, Chinese Academy of Sciences. The first author of the article is a Ph.D. student in the University of Brown.

[This article highlights]

By analyzing the interaction between molecules, the researchers selected a triblock copolymer Pluro nic P-123 with a "hydrophilic-hydrophobic-hydrophilic" symmetry structure to be added to the precursor solution to control the perovskite polycrystalline film. The crystallization behavior gives a very flat and dense MAPbI3 perovskite film. At the same time, the triblock copolymer forms a continuous and adjustable network structure at the grain boundary, which inactivates the grain boundary, effectively improving the photoelectric conversion efficiency and environmental tolerance of the device. The photoelectric conversion efficiency of the perovskite thin film device modified by the grain boundary reached 19.4%, and the illumination was maintained at a standard sunlight source for 480 hours, and the efficiency was maintained at 92%. At the same time, such grain boundary modified films exhibit excellent humidity stability, light stability and thermal stability.

[Graphic introduction]

Figure 1. Schematic and structural model of the modified grain boundary of triblock copolymer

Schematic diagram of a triblock copolymer forming a passivation network along the grain boundaries in a MAPbI3 film

Hydrogen bonding between B triblock polymer and perovskite

C. Schematic diagram of calculation model for calculating the interaction energy between perovskite molecules and triblock polymers

Figure 2. Material characterization of the optimal doping amount of the triblock polymer (0.5% wt)

XRD pattern of the optimal doping amount (0.5%wt) of perovskite film of A triblock polymer

B Triblock polymer optimal doping amount (0.5% wt) FTIR spectrum

SEM image of perovskite film with optimal doping amount (0.5%wt) of C triblock polymer

D-triblock polymer optimal doping amount (0.5%wt) of perovskite film AFM image

Figure 3. TEM characterization of perovskite films doped with different amounts of triblock polymers

Low-magnification TEM image of A optimal doping amount (0.5%wt) of perovskite film

High-power TEM image of perovskite film with different doping amount of BD (0 wt%, 0.5% wt, 1.0% wt, 10% wt)

Electron energy loss spectrum of oxygen in perovskite film with optimal doping amount (0.5%wt)

Figure 4. Structure and characterization of a perovskite solar cell doped with an optimal amount of triblock copolymer

Cross-sectional SEM image of A optimally doped triblock copolymer perovskite battery

B JV curve of different triblock copolymer doping amount battery devices

JV curve of C-optimal doping amount of triblock copolymer perovskite battery device

E-optimal doping amount of triblock copolymer perovskite battery device EQE and integrated current

Figure 5. Stability test of a perovskite film doped with an optimal amount of triblock copolymer (undoped perovskite film is blank)

A Wet stability test: 70% RH

B Thermal stability test: 100 ° C

C Light Stability Test: A Standard Sun

Efficiency graph of D-doped 0.5% wt P123 MAPbI3 solar cell under simulated standard sunlight for 480h

【summary】

The researchers rationally selected the triblock copolymer Pluro nic P-123 with a "hydrophilic-hydrophobic-hydrophilic" symmetry structure to be doped into the MAPbI3 perovskite precursor solution to regulate the film formation process and obtain extremely flattening. A dense perovskite polycrystalline film. At the same time, the polymer forms a continuous passivation network along the grain boundaries of the polycrystalline film, and the perovskite film with the grain boundary modification exhibits excellent environmental tolerance. This research further advances the research progress of functional modification of grain boundaries to improve the stability of perovskite materials and devices, and provides new ideas for the future fabrication of photovoltaic devices with low cost, high photoelectric conversion efficiency and stable outdoor environment.