Low-Temperature Approach to High-Yield and Reproducible Syntheses of High-Quality Small-Sized PbSe Colloidal Nanocrystals for Photovoltaic Applications

Abstract

Small-sized PbSe nanocrystals (NCs) were syn-thesized at low temperature such as 50−80 °C with high reaction yield (up to 100%), high quality, and high synthetic reproducibility, via a noninjection-based one-pot approach. These small-sized PbSe NCs with their first excitonic absorption in wavelength shorter than 1200 nm (corresponding to size < ∼3.7 nm) were developed for photovoltaic applications requiring a large quantity of materials. These colloidal PbSe NCs, also called quantum dots, are high-quality, in terms of narrow size distribution with a typical standard deviation of ∼7−9%, excellent optical properties with high quantum yield of ∼50−90% and small full width at half-maximum of ∼130−150 nm of their band-gap photoemission peaks, and high storage stability. Our synthetic design aimed at promotion of the formation of PbSe monomers for fast and sizable nucleation with the presence of a large number of nuclei at low temperature. For formation of the PbSe monomer, our low-temperature approach suggests the existence of two pathways of Pb−Se (route a) and Pb−P (route b) complexes. Either pathway may dominate, depending on the method used and its experimental conditions. Experimentally, a reducing/nucleation agent, diphenylphosphine, was added to enhance route b. The present study addresses two challenging issues in the NC community, the monomer formation mechanism and the reproducible syntheses of small-sized NCs with high yield and high quality and large-scale capability, bringing insight to the fundamental understanding of optimization of the NC yield and quality via control of the precursor complex reactivity and thus nucleation/growth. Such advances in colloidal science should, in turn, promote the development of next-generation low-cost and high-efficiency solar cells. Schottky-type solar cells using our PbSe NCs as the active material have achieved the highest power conversion efficiency of 2.82%, in comparison with the same type of solar cells using other PbSe NCs, under Air Mass 1.5 global (AM 1.5G) irradiation of 100 mW/cm2.

Bright Gradient-Alloyed CdSexS1–x Quantum Dots Exhibiting Cyan-Blue Emission

“…Sample purification was performed and presented in Supporting Information page S10. 31 PN M Rw i t h 1 H Decoupling. The measurements were performed on a Bruker AV-III 400 spectrometer operating at 161.98 MHz for 31 P. An external standard 85% H 3 PO 4 was used.…”

Low-Temperature Noninjection Approach to Homogeneously-Alloyed PbSexS1−x Colloidal Nanocrystals for Photovoltaic Applications

“…Such an experimental result seems to be in agreement with the argument that pure tertiary phosphine selenide SedPR a3 such as TOPSe or TBPSe did not react with Pb(oleate) 2 , but secondary phosphine selenide Se=PH(R a ) 2 such as DOPSe or DBPSe did. 19,24 Supporting Information Scheme S2 shows our corresponding 31 P NMR study of the three Se solutions used in the Figure 2 batches. The 31 P NMR spectra demonstrate that no DBPSe was detected in Batch 1 SeTBP 99% solution and in Batch 2 solution, while DBPSe was detected in Batch 3 SeTBP 97% solution.…”

“…This concept is represented by eq (bM) where DPP was used instead of TBP 97%. 19,22,23 Accordingly, for the present synthesis of homogeneously alloyed PbSe x S 1Àx with low-cost and air-stable TAA as the S precursor, we selected TBP 97% to prepare the Se precursor TBPSe (with the feed molar ratio of 1 Se-to-2.2 TBP). Also, we used DPP as a reducing agent to promote the formation of PbÀP complex which exhibited much higher reactivity than Pb(oleate) 2 and thus to further tune the reactivity match of the Se and S precursors at low temperature.…”

“…Also, the mean size was estimated by Scherrer equation, 25 which is 3.32 nm by (220) It is acknowledged that discrepancy exists in size determination among various methods or different research groups. 19,26,27 The comparison of the growth kinetics of PbSe, PbS and PbSe x S 1Àx NCs from the eq 2 approach is shown in Supporting Information Figure S2. It is clear that with the use of DPP, the eq 2 approach is excellent for the formation of ternary PbSe x S 1Àx NCs at 60°C.…”

“…It is known that a high degree of monomer supersaturation can lead to the presence of a large number of nuclei and thus the formation of small-sized NCs with high particle yield. 19 Herein, we report on the development of a noninjection one-pot approach to prepare homogeneously alloyed PbSe x S 1-x NCs with bandgap in the range of 1000À1200 nm, aiming at their potential in solar cell applications. This low-temperature approach which can be carried out with long growth periods is more environmentally benign and can be achieved at low-cost with the use of TAA as S source.…”