Abstract
A series of lead-halide based hybrid polyelectrolytes was prepared and used as interfacial layers in organic solar cells (OSCs) to explore their effect on the energy band structures and performance of OSCs. Nonconjugated polyelectrolytes based on ethoxylated polyethylenimine (PEIE) complexed with PbX2 (I, Br, and Cl) were prepared as polymeric analogs of the perovskite semiconductors CH3NH3PbX3. The organic/inorganic hybrid composites were deposited onto Indium tin oxide (ITO) substrates by solution processing, and ultraviolet photoelectron spectroscopy (UPS) measurements confirmed that the polyelectrolytes allowed the work function of the substrates to be controlled. In addition, X-ray photoelectron spectroscopy (XPS) results showed that Pb(II) halide complexes were present in the thin film and that the Pb halide species did not bond covalently with the cationic polymer and confirmed the absence of additional chemical bonds. The composite ratio of organic and inorganic materials was optimized to improve the performance of OSCs. When PbBr2 was complexed with the PEIE material, the efficiency increased up to 3.567% via improvements in open circuit voltage and fill factor from the control device (0.3%). These results demonstrate that lead-halide based polyelectrolytes constitute hybrid interfacial layers which provide a novel route to control device characteristics via variation of the lead halide composition.
Highlights
Organic solar cells (OSCs) offer many advantages as an alternative energy technology
These results demonstrate that lead-halide based polyelectrolytes constitute hybrid interfacial layers which provide a novel route to control device characteristics via variation of the lead halide composition
The first iterations of OSCs involved active layers consisting of 2-dimensional donor/acceptor bilayers [7], but the most effective active layer structure which has emerged is the bulk heterojunction (BHJ), which consists of a 3-dimensionsal blend of donor and acceptor materials which offers increased efficiency due to the large donor/acceptor interfacial area [8,9]
Summary
Organic solar cells (OSCs) offer many advantages as an alternative energy technology. Lead halide perovskite (LHP) semiconductors, which are known to have remarkably good electronic properties such as high-charge carrier mobilities [34], low-charge carrier recombination rates, and large carrier diffusion lengths [35], as well as tunable energy band structures [36], are based on combinations of Pb(II) halide salts and halides of organic cations such as methylammonium iodide (MAI) or formamidinium iodide. This type of semiconductor can be formed by mixing two components in a suitable solvent and allowing the solvent to evaporate.
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