Abstract
First-principles electronic band calculations were used to investigate the effects of alkali metals and organic cations added to Cu-based perovskite solar cells. The copper d-orbital band was slightly above the valence-band maximum and functioned as an acceptor level for carrier generation. Excitation from iodine p-orbitals and copper d-orbitals to alkali metal s-orbitals could suppress carrier recombination and promote carrier transport. Experimental solar conversion efficiencies increased after adding both Cu and Na, in agreement with the calculations. Total-energy calculations indicated that the perovskite crystal stability increased with the addition of ethyl ammonium, although the total energy decreased with the addition of Cu and Na.
Highlights
There have been many efforts to improve the conversion efficiencies and durabilities of perovskite photovoltaic devices by adding metal, halogen, and organic ions to the precursor solutions [1–3]
Lattice distortion in the perovskite crystals was reduced by small amounts of Cu, and lattice defects were suppressed with Na at the defect sites after desorption of methylammonium (MA), which improved conversion efficiency and device durability
For MAPbI3, the energy gap increased when I was replaced with Br or
Summary
There have been many efforts to improve the conversion efficiencies and durabilities of perovskite photovoltaic devices by adding metal, halogen, and organic ions to the precursor solutions [1–3]. Other approaches have included the development of scalable processes via electrodeposition [4,5], stable fully inorganic perovskites [6], polymer composites using perovskites [7], and solvent effects in the precursor solution on perovskite film microstructures [8] Additives such as copper (Cu), sodium (Na), and ethyl ammonium (EA) were examined. Monovalent pseudo-halogens, such as thiocyanate, have properties like those of halogens, they could improve photoelectric conversion and stability, and may prevent oxidation of Sn2+ to Sn4+ in Sn-based perovskites [45]. The latter was expected to suppress oxidation-induced degradation. Both total- and partial-substitution structure models approximating perovskite compositions in actual devices were used to investigate the effects
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