Abstract
Organic semiconductors are commonly used as charge-extraction layers in metal-halide perovskite solar cells. However, parasitic light absorption in the sun-facing front molecular layer, through which sun light must propagate before reaching the perovskite layer, may lower the power conversion efficiency of such devices. Here, we show that such losses may be eliminated through efficient excitation energy transfer from a photoexcited polymer layer to the underlying perovskite. Experimentally observed energy transfer between a range of different polymer films and a methylammonium lead iodide perovskite layer was used as basis for modelling the efficacy of the mechanism as a function of layer thickness, photoluminescence quantum efficiency and absorption coefficient of the organic polymer film. Our findings reveal that efficient energy transfer can be achieved for thin (≤10 nm) organic charge-extraction layers exhibiting high photoluminescence quantum efficiency. We further explore how the morphology of such thin polymer layers may be affected by interface formation with the perovskite.
Highlights
Organic semiconductors are commonly used as charge-extraction layers in metal-halide perovskite solar cells
We find that for thin (≤10 nm) organic charge-extraction layers that exhibit high PL quantum efficiency (PLQE), much of the absorbed energy is transferred to the Metal-halide perovskites (MHPs) layer, meaning that energy transfer (ET) can be used as an effective tool to mitigate absorption losses in charge-transport layers (CTLs)
To explore excitation ET between a conjugated polymer layer and MAPbI3, we investigated four different polymers that have been commonly used in optoelectronic devices, namely Super Yellow (PDY-132, a poly(1,4-phenylenevinylene)-based light-emitting copolymer developed by Merck Chemicals), F8BT (poly(9,9-dioctylfluorenealt-benzothiadiazole)), P3HT (poly(3-hexylthiophene-2,5-diyl)) and PTAA ((poly[bis(4-phenyl)(2,4,6-trimethylphenyl) amine]))
Summary
Organic semiconductors are commonly used as charge-extraction layers in metal-halide perovskite solar cells. Using PL transient-decay measurements, we calibrate the global input parameters of the formulae and show that the mathematical formalism well describes our data We use these results to model the ET efficiencies as a function of different parameters, namely polymer film thickness, L, polymer PL quantum efficiency (PLQE), φd and the absorption coefficient of the polymer at the wavelength of the incoming light, α(λexc). We find that for thin (≤10 nm) organic charge-extraction layers that exhibit high PLQE, much of the absorbed energy is transferred to the MHP layer, meaning that ET can be used as an effective tool to mitigate absorption losses in CTLs. To explore if the morphology of such thin polymer layers is affected by interface formation with an MHP, we further conduct a careful analysis of the PL spectra of P3HT (poly(3-hexylthiophene-2-5-diyl)) for a range of film thicknesses, highlighting subtle conformational changes
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