JOUL, Volume 2

Supplemental Information

Efficient Blue and White

Perovskite Light-Emitting

Diodes via Manganese Doping

Shaocong Hou, Mahesh K. Gangishetty, Qimin Quan, and Daniel N. Congreve

400 420 440 460 4801E-3

0.01

0.1

1

10Thermodynamic limit

0.09%

0.19%

0.25%

1.5%

Mn

/ E

xc

ito

n e

mis

sio

n

Excitonic peak (nm)

Mn:CsPbCl3

Fig. S1. Effect of different Mn doping methods on emission properties of perovskite nanocrystals.

Black squares are the emission of nanocrystals doped by single-step hot-injection method. Colored

open labels are the emission of nanocrystals synthesized by PbBr2 exchanging of Mn:CsPbCl3 (red

circle) or y% Mn:CsPbCl3-xBrx at different stages of exchanging after hot-injection. Blue triangle:

y = 1.5%, magenta triangle: y = 0.25%, olive diamond: y = 0.19%. The Mn/exciton emission ratio

of sample y = 0.09% is approximately zero but is included on the horizontal axis to indicate the

emission peak position. The emission ratio was used to track Mn doping concentration, which was

calculated from the relative peak heights of the emission of nanocrystal solutions without

purification. The black dash line indicates the boundaries of thermodynamic doping limits by the

single-step hot-injection method.

Fig. S2. Cartoon of the proposed mechanism of higher Mn doping into perovskite nanocrystals,

consisting of the following steps: (1) Synthesis of Cl-rich perovskite with a high Mn doping level

by hot-injection method. (2,3) Due to the low formation energy and migration active energy of

chloride vacancies,1,2 Cl-rich perovskites have abundant intrinsic chloride-vacancies and could be

attacked by ligands in the solution. The bromide anion or lead bromide precursors could attach to

these vacancies. (4) The halide anions (Cl/Br) has higher mobility than Pb/Mn, thus the Cl-to-Br

exchange happens faster than Mn-to-Pb. (5) The Cl/Br and Pb/Mn diffuse within the nanocrystals.

The above exchange process was quenched within 10-30 min, when the halide exchange was

completed but the Pb/Mn exchange was still in process. Br-rich perovskite nanocrystals with

higher Mn doping levels were thus obtained.

Fig. S3. Thin film photoluminescence of the nanocrystals with various Mn doping.

Fig. S4. Redshift of emission in time for each of the nanocrystal samples presented in this work.

Undoped samples (top left) show significant red-shifting in time. Combined with the lack of such

a red-shifting in solution, we assign this to polydispersity within the nanocrystal sample leading to

inter-nanocrystal transfer. Doped samples do not show this red-shifting.

Fig. S5. Luminescence lifetime of the long-lived Mn emission as a function of nanocrystal

preparation. Thin film shows a reduced lifetime relative to solution, and TFB/PFI thin film shows

further reductions in the lifetime, correlating with the reduced PL in thin film shown in Figure S3

and no Mn observed in the EL, Figure 4.

Fig. S6. Full electroluminescence spectrum of the LEDs. No Mn electroluminescence is

observed.

Fig. S7. Electroluminescence measured on a 0.19% Mn device at increasing bias voltages. We see

little change in spectrum, as the peak moves approximately 2 nm at a very high 13V applied bias.

Fig. S8. Stability of the 0.19% Mn device. The electroluminescence was measured on a packaged

device at a current density of 1 mA/cm2. Mn doping seems to impact a moderate stability increase

in operational stability (top) and a significant increase in color stability (bottom).

Fig S9. Stability of the downconverters. The downconverters were illuminated by a 445 nm laser

in air. The green film showed excellent operational and spectral stability, while the red film gently

decreased in time. The red film emission slightly blueshifted by approximately 2 nm over the hour.

ICP Mn

Content

PbBr2

(mg)

PbCl2

(mg)

MnCl2

(mg)

PbBr2

(mmol)

PbCl2

(mmol)

MnCl2

(mmol)

Molar ratio

Mn/Pb

0% 165 83.6 0 0.450 0.301 0 0

0.09% 210 0 50 0.572 0 0.397 0.694

0.19% 210 0 70 0.572 0 0.556 0.972

0.25% 210 0 80 0.572 0 0.636 1.111

1.5% 210 0 90 0.572 0 0.715 1.250

Table S1. Typical amount of precursors for five nanocrystal samples

Abnormal quenching of Mn2+ dopant emission

Under weak excitation conditions, the rate equation of perovskite excitonic states (nex) and Mn2+

dopant excitation states (nMn) can be simplified as following, assuming there is no multi-

exciton/higher exciton-state generation, exciton-exciton interaction, and dopant-dopant

interaction.

𝑑𝑛𝑒𝑥𝑑𝑡

= 𝐺 − 𝑘𝑟,𝑒𝑥𝑛𝑒𝑥 − 𝑘𝑛𝑟,𝑒𝑥𝑛𝑒𝑥 −𝑁𝑘𝑡𝑛𝑒𝑥

𝑑𝑛𝑀𝑛𝑑𝑡

= 𝑁𝑘𝑡𝑛𝑒𝑥 − 𝑘𝑟,𝑀𝑛𝑛𝑀𝑛 − 𝑘𝑛𝑟,𝑀𝑛𝑛𝑀𝑛

Where G is the exciton generation rate under electrical or optical pumping; kr,ex, knr,ex and kt are

the radiative recombination rate, nonradiative decay rate from the perovskite excitonic state and

the exciton-to-Mn2+ energy transfer rate, respectively; kr,Mn and knr,Mn are the radiative

recombination rate and nonradiative decay rate from the Mn excited state, respectively, and N is

the average number of Mn2+ dopants in each perovskite nanocrystal.

In a steady-state condition, 𝑑𝑛𝑒𝑥

𝑑𝑡= 0 and

𝑑𝑛𝑀𝑛

𝑑𝑡= 0; then,

𝑛𝑒𝑥 =𝐺

𝑘𝑟,𝑒𝑥 + 𝑘𝑛𝑟,𝑒𝑥 +𝑁𝑘𝑡

𝑛𝑀𝑛 =𝑁𝑘𝑡𝑛𝑒𝑥

𝑘𝑟,𝑀𝑛 + 𝑘𝑛𝑟,𝑀𝑛

Where the density of dopant excitation states has upper boundary at the dopant density in

nanocrystals (N0,Mn), that is, nMn ≤ N0,Mn. Photon emission rates from the perovskite excitonic state

(pex) and Mn2+ dopant state (pMn) can be calculated from

𝑝𝑒𝑥 = 𝑘𝑟,𝑒𝑥𝑛𝑒𝑥 and 𝑝𝑀𝑛 = 𝑘𝑟,𝑀𝑛𝑛𝑀𝑛

The emission ratio from two states is then

𝑝𝑒𝑥𝑝𝑀𝑛

=𝑘𝑟,𝑒𝑥𝑛𝑒𝑥𝑘𝑟,𝑀𝑛𝑛𝑀𝑛

=𝑘𝑟,𝑒𝑥𝑘𝑟,𝑀𝑛

𝑘𝑟,𝑀𝑛 + 𝑘𝑛𝑟,𝑀𝑛𝑁𝑘𝑡

=𝑘𝑟,𝑒𝑥𝑁𝑘𝑡

(1 +𝑘𝑛𝑟,𝑀𝑛𝑘𝑟,𝑀𝑛

)

Given the emission efficiency from two states: ф𝑒𝑥 =𝑘𝑟,𝑒𝑥

𝑘𝑟,𝑒𝑥+𝑘𝑛𝑟,𝑒𝑥+𝑁𝑘𝑡 and ф𝑀𝑛 =

𝑘𝑟,𝑀𝑛

𝑘𝑟,𝑀𝑛+𝑘𝑛𝑟,𝑀𝑛

(Note: photoluminescence quantum yield: 𝑃𝐿𝑄𝑌𝑒𝑥 = ф𝑒𝑥, 𝑃𝐿𝑄𝑌𝑀𝑛 =𝑁𝑘𝑡

𝑘𝑟,𝑒𝑥+𝑘𝑛𝑟,𝑒𝑥+𝑁𝑘𝑡

𝑘𝑟,𝑀𝑛

𝑘𝑟,𝑀𝑛+𝑘𝑛𝑟,𝑀𝑛= ф𝑡ф𝑀𝑛), the ratio can also be rewritten as

𝑝𝑀𝑛𝑝𝑒𝑥

=𝑁𝑘𝑡𝑘𝑟,𝑒𝑥

ф𝑀𝑛

The intrinsic exciton decay rate (kr,ex) is mainly determined by the chemical/crystalline structure

of the perovskite nanocrystals. The number of Mn dopants in each nanocrystal (N) is proportional

to the Mn doping level. The rate of exciton-to-dopant energy transfer (kt) is a function of the

distance between an exciton and a Mn2+ dopant as well as the wavefunction properties of exciton

and the Mn2+ dopant; non-radiative decay rates knr,ex and knr,Mn are very sensitive to defects/traps

in the bulk and at the surface and thus are affected by processing conditions.3

We and others4 observed that the PLQYex and PLQYMn of perovskite nanocrystals in colloidal

solutions increased as moderate Mn2+ doping is introduced. Thus, we conclude that moderate Mn2+

doping reduces knr,ex and knr,Mn, that is, the intrinsic defects/traps in blue perovskite nanocrystals,

which is consistent with the photophysics of Mn-doped perovskites.5

We also observed that the emission of the perovskite nanocrystals was significantly quenched after

deposition into solid-state thin films, which is usually blamed on the structure/ligands of the

perovskite and inter-nanocrystal energy transfer. However, it is interesting to find that Mn2+

emission was quenched much more seriously than the excitonic emission. The unequal quenching

of exciton emission and Mn2+ dopant emission can be explained by the above equation, where the

emission photon ratio from the perovskite exciton state and Mn2+ dopant state is primarily decided

by фMn, that is, knr,Mn/kr,Mn. It is reasonable to expect that the long-lived Mn2+ dopant excitation

state is more sensitive to the traps/defects created during film deposition. From the Mn2+ transient

PL (Fig. S4), we extracted radiative and non-radiative decay lifetimes from the Mn2+ state. The

Mn2+ radiative decay lifetime in solution was 520 μs. After deposition into thin films, a bi-

exponential decay appeared, with a fast decay process with a lifetime of 170 μs and a longer decay

with a lifetime of 400 μs. We tentatively attribute the latter to Mn2+ radiative emission and the

former to enhanced non-radiative decay of a sub-population of the excitons, resulting in greatly

reduced Mn2+ emission in thin films. Combining the advantage of the perovskite excitonic

emission tolerance to traps/defects, we can use this quenching to our advantage to maintain a pure

and intense blue excitonic emission. Thanks to this unequal quenching effect, it is possible to

optimize Mn doping concentration to achieve pure blue excitonic emission without contamination

from Mn emission.

Overcoming the thermodynamic limit of Mn2+ doping concentration

Although the passivation mechanism of Mn2+ is still under investigation, the benefit of Mn2+

doping on the perovskite excitonic emission clearly increases with the Mn2+ concentration. Given

a fixed blue excitonic emission at ca. 469 nm (in CsPbClxBr3-x nanocrystals), we have observed

that the doping is limited to a low level for a single-step hot-injection method (Black squares in

Fig. S1). This doping level was found to be smaller than the optimum level for the best LED

performance. Thus, it is important to increase the doping level to achieve optimum optoelectronic

performance. Here, to increase the doping level, we take the advantage of the high thermodynamic

doping concentration of Mn2+ in Cl-rich perovskites and then the kinetically post-exchange the Cl-

by Br- in the presence of PbBr2. During the post-exchanging process, the halide (Cl-to-Br)

exchanging process occurs faster than the Mn-to-Pb exchanging process. The proposed mechanism

of post-exchanging process is illustrated in Fig. S2, and two benefits could be observed: (1)

aligning the excitonic emission back to ca. 469 nm; (2) overcoming the thermodynamic doping

limit of Mn2+ for a single-step hot-injection. It is noted that the extra ligands and unreacted

precursors during the post-exchange usually require more intense purification by anti-solvent to

increase the conductivity, which is not friendly to the electronic properties of the nanocrystals. To

balance the results from purification process, we find that it is essential to start the post-exchange

process from Mn doped Cl/Br alloyed perovskite pre-synthesized by hot-injection, instead of

Mn:CsPbCl3.

References

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CdS/ZnS Core/Shell Nanocrystals: Surface Effects and Position‐Dependent Properties.

Chem. – A Eur. J. 15, 3186–3197 (2009).

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