Abstract
Metal halide perovskite semiconductors possess outstanding characteristics for optoelectronic applications including but not limited to photovoltaics. Low-dimensional and nanostructured motifs impart added functionality which can be exploited further. Moreover, wider cation composition tunability and tunable surface ligand properties of colloidal quantum dot (QD) perovskites now enable unprecedented device architectures which differ from thin-film perovskites fabricated from solvated molecular precursors. Here, using layer-by-layer deposition of perovskite QDs, we demonstrate solar cells with abrupt compositional changes throughout the perovskite film. We utilize this ability to abruptly control composition to create an internal heterojunction that facilitates charge separation at the internal interface leading to improved photocarrier harvesting. We show how the photovoltaic performance depends upon the heterojunction position, as well as the composition of each component, and we describe an architecture that greatly improves the performance of perovskite QD photovoltaics.
Highlights
Metal halide perovskite semiconductors possess outstanding characteristics for optoelectronic applications including but not limited to photovoltaics
The perovskite compositions of the film structure are reversed compared to Fig. 1c, and here it is clear that a similar interface is formed within the film stack with the diminishment of the FA signal along with a slight increase in the Cs signal. This indicates a clear interface between layers of quantum dot (QD) with different compositions is formed and the sequence of these two QD layers can be controlled via layer-by-layer deposition
We find the carriers in the more FAcontaining films possess longer free-carrier lifetimes and exhibit lower effective mobility compared to pure CsPbI3 QD films (Supplementary Fig. 9)
Summary
Metal halide perovskite semiconductors possess outstanding characteristics for optoelectronic applications including but not limited to photovoltaics. Using layer-by-layer deposition of perovskite QDs, we demonstrate solar cells with abrupt compositional changes throughout the perovskite film We utilize this ability to abruptly control composition to create an internal heterojunction that facilitates charge separation at the internal interface leading to improved photocarrier harvesting. In photovoltaic (PV) devices, energy band engineering can enable better harvesting of photogenerated charge carriers[4,5,6] This concept is especially prevalent in vapor deposited heterostructures using MOCVD and MBE of III–V semiconductors[7] as well as in sputtered or thermally evaporated systems such as CIGS where the composition at surfaces can be altered to promote a buried location for the actual p-n charge separating junction[8,9]. The second (or any subsequent) solution can contain either the same QDs or QDs of different composition allowing for the composition of the perovskite film to be modulated in almost any desired order throughout the film thickness
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