Molecular Doping of the Hole-Transporting Layer for Efficient, Single-Step-Deposited Colloidal Quantum Dot Photovoltaics

Abstract

Employment of thin perovskite shells and metal halides as surface-passivants for colloidal quantum dots (CQDs) has been an important, recent development in CQD optoelectronics. These have opened the route to single-step-deposited high-performing CQD solar cells. These promising architectures employ a CQD hole-transporting layer (HTL) whose intrinsically shallow Fermi level (E F ) restricts band-bending at maximum power-point during solar cell operation limiting charge collection. Here, we demonstrate a generalized approach to effectively balance band-edge energy levels of the main CQD absorber and chargetransport layer for these high-performance solar cells. Briefly soaking the CQD HTL in a solution of the metal−organic p-dopant, molybdenum tris(1-(trifluoroacetyl)-2-(trifluoromethyl)ethane-1,2-dithiolene), effectively deepens its Fermi level, resulting in enhanced band bending at the HTL:absorber junction. This blocks the back-flow of photogenerated electrons, leading to enhanced photocurrent and fill factor compared to those of undoped devices. We demonstrate 9.0% perovskite-shelled and 9.5% metal-halide-passivated CQD solar cells, both achieving ca. 10% relative enhancements over undoped baselines.

Improved Processability and Efficiency of Colloidal Quantum Dot Solar Cells Based on Organic Hole Transport Layers

“…The Fermi levels and the highest occupied molecular orbital (HOMO) levels were determined from the onsets of the secondary electron cutoff region and the low binding energy region of UPS analysis results ( Figure S1a,b, Supporting Information), and the lowest unoccupied molecular orbital (LUMO) levels were determined by HOMO levels and optical bandgap from absorption spectra ( Figure S1c, Supporting Information). [29] We also determined the hole mobility of PTB7 and P3HT by a space-charge-limited current (SCLC) analysis of a hole-only device with a structure of indium-doped tin oxide (ITO)/HTLs/Au ( Figure S2, Supporting Information). [27,28] The HOMO levels of polymer HTLs were appropriate to extract holes from i-CQDs, while the LUMO levels of polymer HTLs were sufficiently high to block electron back transfer from i-CQDs.…”

Molecular Engineering in Hole Transport π‐Conjugated Polymers to Enable High Efficiency Colloidal Quantum Dot Solar Cells

“…Device and Optical Simulation : SCAPS software (3.3.07 version) was used to simulate the CQDSC performance parameter under AM 1.5G 100 mW cm −2 illumination with respect to HOMO level and hole mobility . The parameters used in this simulation was obtained from the previous report, with slight modification, and are summarized in Table S3 of the Supporting Information.…”

Overcoming the Ambient Manufacturability‐Scalability‐Performance Bottleneck in Colloidal Quantum Dot Photovoltaics

“…The CQD solar cell architecture is schematized in Figure a. Absorber layer comprises of PbS CQDs capped with lead halide ligands (PbX 2 , X = I, Br), obtained via SolEx . Details of device fabrication are available in the Experimental Section (Supporting Information) and were kept the same year‐round in all locations .…”