Efficient energy transfer mitigates parasitic light absorption in molecular charge-extraction layers for perovskite solar cells

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.

Phase segregation in mixed-halide perovskites affects charge-carrier dynamics while preserving mobility

“…As part of an overall light managing strategy within a complete multi-junction solar cell, low-energy photons emitted by the I-rich phase of the mixed-halide perovskite layer may be effectively recaptured within the narrow-bandgap cell of the tandem device. Such a transfer process between different absorber layers in the device could occur through either photon emission and reabsorption 46 , or direct resonance energy transfer 52 . In this scenario, the combined multi-junction performance could compensate for some of the losses incurred in the wide-bandgap mixed halide absorber, provided the overall architecture is optimised taking such transfers into account.…”

A Comparison of Charge Carrier Dynamics in Organic and Perovskite Solar Cells

“…[97,98] This PL quenching can be used as an assay of the efficiency of charge extraction in complete PSCs. [98][99][100][101][102] For both efficient OSCs and PSCs, absolute PL quantum yields are relatively low, even at open circuit (typically <<10%), [103] indicating that for both devices radiative recombination (of either excitons or charges) is not the primary limit to practical device efficiency (although they do impose limits on theoretically achievable efficiencies). PSCs typically exhibit higher electroluminescence (EL) yields than OSCs, [104,105] consistent with the greater dominance of radiative rather than nonradiative charge recombination in these devices.…”

First Demonstration of Top Contact-Free Perovskite/Silicon Two-Terminal Tandem Solar Cells for Overcoming the Current Density Hurdle

“…Most of the parasitic absorption in perovskite solar cells is due to the sun-facing carrier transport layer. 37,38 To overcome parasitic absorption, the back-contact concept has recently been adapted in perovskite solar cells. To maximize light absorption at the absorber layer without parasitic absorption, a back-contact perovskite solar cell (BC-PSC) was first reported in 2016 with 6.54% efficiency.…”

“…Conventional perovskite solar cells are based on a planar architecture in which a perovskite absorber layer of several hundred nanometers thickness is positioned between two different carrier transport materials, namely, the electron transport layer (ETL) and hole transport layer (HTL). Most of the parasitic absorption in perovskite solar cells is due to the sun-facing carrier transport layer. , To overcome parasitic absorption, the back-contact concept has recently been adapted in perovskite solar cells. To maximize light absorption at the absorber layer without parasitic absorption, a back-contact perovskite solar cell (BC-PSC) was first reported in 2016 with 6.54% efficiency .…”