*** Hot-electron transfer in quantum-dot heterojunction films *** 
Authors: G. Grimaldi, M. van Ouwendorp
Optoelectronic material section, Chemical Engineering department, Faculty of Applied Science
Delft University of Technology 
Corresponding author: G. Grimaldi 
Contact Information: g.grimaldi@tudelft.nl 
Delft University of Technology - Faculty of Applied Science

***General Introduction***
It is being made public both to act as supplementary data for publications and the PhD thesis of G. Grimaldi and in order for other researchers to use this data in their own work. 
***Purpose of the test campaign***
Characterise the presence of hot-electron injection across a heterojunction QD film, i.e. a film composed of two different QD materials.
***Test equipment***
The absorption measurements were performed in a Lambda 900 spectrophotometer, measuring the samples inside an integrating sphere, to correct for sample scattering and reflection. The film were stored inside air-tight sample holders, to prevent degradation of the air-sensitive QD components.
The transient absorption measurements were performed inside a Helios measurement box (Ultrafast Systems). The output of a Yb:KGW oscillator (180 fs, 1028 nm, 5kHz, Pharos SP, Light Conversion) is split into a pump and probe beam by a beam splitter. The pump is converted into tunable wavelength output by an OPA, equipped with a second harmonic module (Orpheus, Light Conversion). The probe beam is sent towards a white-light generation crystal and converted into a broadband spectrum. The pump beam is further chopped with a 2.5kHz chopper, blocking one every two pump pulses. The pump and probe come towards the sample with a small angle between them. The time of arrival of the two beams is controlled varying the length of the pump path via mirrors mounted on a delay stage. After transmission through the sample, the probe beam is collected by a detection path, while the pump beam is dumped.
The spectroelectrochemistry measurements are performed inside a nitrogen filled glovebox. A halogen light is used as light source. The sample, a QD film grown on top of a conductive ITO substrate, is connected to the working electrode of a potentiostat and placed in a cuvette filled with a 0.1 M solution of lithium perchlorate in acetonitrile. A platinum electrode, parallel to the sample, acts as a counter-electrode, while a silver wire located between them acts as reference electrode. A light beam passes through the sample and is collected at a detector. Measuring the intensity of the transmitted light as the potential is scanned and comparing it to the intensity value at open-circuit potential allows to obtain the absorbance changes as a function of the applied potential.
***Description of the data in this data set***

— Sample codes

PCM6 —> PbSe - CdSe heterojunction QD film , EDT capped
PM7 —> PbSe QD film , EDT capped
CM4 —> CdSe QD film , EDT capped
PCM11 —> PbSe - CdSe heterojunction QD film , EDA capped
PM13 —> PbSe QD film , EDA capped
CM8 —> CdSe QD film , EDA capped

— Absorption measurements

The absorption files contain a long header, up to the line containing “#DATA”, followed by two column of data: the first one contains wavelengths (in nm), the second one contains absorbance values.

Absorption spectra are obtained measuring the samples, stored in airtight sample holders, inside an integrating sphere. The raw absorption spectra obtained need to be corrected for the absorption spectrum of the holder containing a blank substrate.

The absorption spectrum of sample CM4 is already corrected for the absorbance of the sample holder, which was kept in the integrating sphere during the auto zero scan. The absorption spectrum is corrected for an absorption offset, estimated by the remaining amount of absorption within the CdSe bandgap, in particular at 660nm.

The absorption spectrum of sample PCM6 needs to be corrected by the absorption spectrum of holderA. The resulting absorption spectrum is corrected for an absorption offset, estimated by the remaining amount of absorption within the PbSe bandgap, in particular at 1340nm.

The absorption spectrum of sample PM7 needs to be corrected by the absorption spectrum of holderA. The resulting absorption spectrum is corrected for an absorption offset, estimated by the remaining amount of absorption within the PbSe bandgap, in particular at 1340nm.

The absorption spectrum of sample PCM11 needs to be corrected by the absorption spectrum of blank. The resulting absorption spectrum is corrected for an absorption offset, estimated by the remaining amount of absorption within the PbSe bandgap, in particular at 1310nm.

The absorption spectrum of sample CM4 needs to be corrected by the absorption spectrum of blank1. The absorption spectrum is corrected for an absorption offset, estimated by the remaining amount of absorption within the CdSe bandgap, in particular at 660nm.

The absorption spectrum of sample PM13 needs to be corrected by the absorption spectrum of blank1. The resulting absorption spectrum is corrected for an absorption offset, estimated by the remaining amount of absorption within the PbSe bandgap, in particular at 1310nm.


— Transient Absorption measurements

Each transient absorption measurement is stored in a .csv file, whose name contains the name of the sample, the excitation wavelength, the power of the full pump beam and the range of detection (visible: VIS, near infrared: NIR). Inside the .csv file, data are organized in a matrix. The 0x0 cell is empty. The rest of the first row contains the value of the time points, expressed in ps. The rest of the first column contains the values of the wavelength, expressed in nm. The rest of the matrix contains differential absorbance values. 
For example: if the cell 0xn contains the value 0.2, and the cell mx0 contains the value 750, the cell mxn will contain the differential absorbance of the light at 750nm measured 0.2 ps after photo excitation.
NaN values correspond to portion of the detector range where the intensity of the probe light was 0.

The power density estimate is performed measuring the power transmitted through a 2mm pinhole, and dividing the transmitted power by the area of the pinhole. The power transmitted through the 2mm pinhole can be found in the Measurement on… word files, listing the main parameters of each measurement performed, ordered per measurement day (top of the document) or on per excitation wavelength (bottom of the document).


— Spectroelectrochemistry measurements

The spectroelectrochemistry measurements are organized in the following way:

1) the top folder contains the two CV scans (current vs potential) on an bare ITO substrate immersed in 0.1 M lithium perchlorate in acetonitrile, with ferracene dissolved in the electrolyte.
2) Each of the folders in the top folders (ITO, PCEC1, PEC1) contains the results of a CV performed on a sample immersed in 0.1 M lithium perchlorate in acetonitrile (no ferracene in solution). The ITO folder contains measurements on a bare ITO substrate, PEC1 measurements on a PbSe QD film capped with EDT on top of an ITO substrate, PCEC1 measurements on PbSe-CdSe heterojunction QD film capped with EDT on top of an ITO substrate.
3) Each one of the measurement folders contain one or more txt files, each containing the results of  CV scan. 
4) The subfolders (either IR or VIS) contain differential absorbance spectra, each one saved as a separate txt file. Each file contains two columns: the first column contains a wavelength (in nm), the second column contains the corresponding differential absorbance. The files are numbered on a temporal basis, meaning that the file named IR_0002.txt is recorded right after IR_0001.txt and right before IR_0003.txt.

CV scan files contains two header names (explaining themselves the format of the data) and two columns of data: the first one contains the applied potential (in V), the second one the current flowing towards the sample (in A).

IMPORTANT NOTE: the number of recorded differential absorbance (dA) file is not equal to the time steps of the CV scan. However, the first dA spectrum is recorded at the first datapoint of the CV scan, and the last dA spectrum is recorded at the last datapoint of the CV scan. Interpolation of the CV data is required to correlate absorption changes to the potential.

The ITO and PEC1 folders contain the results of a single CV scan on each samples. PCEC1 contains the results of three CV scans, performed consecutively on the same sample. The folder labelled as IR_abs and VIS_abs contain the absorption spectrum of the sample in the respective detection range, with the same data format as the dA spectra (first column wavelength, second column absorbance).

NOTE: potential values reported in the article “Hot-electron transfer in quantum-dot heterojunction films” are relative to the work-function of the pseudo reference electrode, as the spectroelectrochemical measurements were used to obtain the relative position in electron-injection potential between two materials within the same film.