Alkali Metal Doping for Improved CH3NH3PbI3 Perovskite Solar Cells.

Wangen Zhao,Dong Yang,Fengyang Yu,Shengzhong Frank Liu,Zhun Yao

doi:10.1002/advs.201700131

Abstract

Organic–inorganic hybrid halide perovskites are proven to be a promising semiconductor material as the absorber layer of solar cells. However, the perovskite films always suffer from nonuniform coverage or high trap state density due to the polycrystalline characteristics, which degrade the photoelectric properties of thin films. Herein, the alkali metal ions which are stable against oxidation and reduction are used in the perovskite precursor solution to induce the process of crystallization and nucleation, then affect the properties of the perovskite film. It is found that the addition of the alkali metal ions clearly improves the quality of perovskite film: enlarges the grain sizes, reduces the defect state density, passivates the grain boundaries, increases the built‐in potential (V bi), resulting to the enhancement in the power conversion efficiency of perovskite thin film solar cell.

Highlights

Introduction defect passivation or reduction ofgrain boundaries (GBs) is critically vital.[16,17,18] In an effort to improve the quality of perovskite absorberOrganic–inorganic hybrid halide perovskites commonly layer, variations of techniques have been developed, which can adopting the ABX3 structure: where A is a monovalent organic or inorganic cation, e.g., methylammonium (MA+), formamidinium (FA+), Cs+ etc.; B is a divalent metal ion (Pb2+, Sn2+, Ge2+ etc.) and X is a monovalent anion (Cl−, Br−, I−, SCN− etc.)be divided into two major types, by and large
To check the quality of perovskite absorber layer, morphological characterization based on field-emission scanning electron microscopy (FE-SEM) was carried out to determine the shape and coverage of the MAPbI3 grains and thin films prepared in the presence of additives and the control sample
Synthesizing above consequences, we found that the additives apparently help to improve the perovskite growth into much large crystallite grains and smoother films

Summary

Results and Discussion

To check the quality of perovskite absorber layer, morphological characterization based on field-emission scanning electron microscopy (FE-SEM) was carried out to determine the shape and coverage of the MAPbI3 grains and thin films prepared in the presence of additives and the control sample (without any additive). Where Nc(W) is the net carrier concentration, q is the electron charge, Ks is the semiconductor dielectric constant, ε0 is the permittivity of free space, A is the area of the solar cell, C is the capacitance, and V is the applied voltage It demonstrates that the alkali metal doped perovskite devices have changed carrier concentration based on above equation, and they have led to a higher built-in voltage (the point of intersection by epitaxy the curve of 1/C2–V when it is equal to zero).

Conclusions

Experimental Section

Conflict of Interest