Abstract
Perovskite solar cells have recently seen rapid improvements in performance with certified efficiencies of above 23%. Fullerene compounds are a very popular electron-transfer material in these devices. In a previous report, it has been shown that while an ultrathin fullerene layer of just 1 nm is sufficient to achieve good device performance, removal of this layer causes a drastic decrease in performance. We provide an explanation to these observed effects by use of a numerical device model. This work provides theoretical support to the experimental understanding of the dominant role of fullerenes in perovskite solar cells.
Highlights
Thin-film photovoltaics based on hybrid halide perovskites have attracted great interest in recent years1–5 due to lower material and production costs than single-crystal devices as well as rapid improvements in perovskite device efficiencies to above 23%
We see that the C60 layer is essential for good device performance and that a 1 nm C60 layer is sufficient for good performance, with only a small improvement achieved when the layer thickness is increased to 20 nm
By systematically studying the effects of interface mobility and trap density on the JV curves, we find that poor electron extraction at the perovskite interface modeled by a decreased carrier mobility is the main cause of the severe decrease in device performance when there is no C60 layer
Summary
Thin-film photovoltaics based on hybrid halide perovskites have attracted great interest in recent years due to lower material and production costs than single-crystal devices as well as rapid improvements in perovskite device efficiencies to above 23%.6 A typical planar heterojunction perovskite solar cell is composed of a perovskite absorber layer sandwiched between an electron transport layer (ETL) and a hole transport layer (HTL). Holes are unlikely to pass into the ETL and electrons are unlikely to pass into the HTL due to energy barriers Both radiative and non-radiative recombination of carriers results in decrease in device performance. Based on fitting of the model to the experimental results, the reason for the differences in performance between the devices with and without C60 is mostly due to a much lower electron mobility at a perovskite/BCP interface than at a perovskite/C60 interface. These results help clarify the role of the C60 layer as part of the ETL in a perovskite solar cell. Radiative recombination is modeled by Langevin bimolecular recombination with the recombination rate given by
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