Merging Passivation in Synthesis Enabling the Lowest Open‐Circuit Voltage Loss for PbS Quantum Dot Solar Cells

Abstract

CQD solutions processability and tunability of physical properties, but also leads to an increased surface area/volume ratio. [4] Consequently, CQDs suffer from high surface trap density, resulting in significantly reduced photovoltaic performance. [5,6] The surface passivation then becomes a critical step to reduce energy loss (e.g., open-circuit voltage [V oc ] loss) and realize high device performance. [7][8][9] Exploring efficient passivation strategies has always been the overarching theme throughout the history of CQD solar cells. [10] However, this issue has far from been solved. Up to now, the V oc loss in high-efficiency PbS CQD solar cells is mostly around 0.45 V, [11][12][13][14][15] which is significantly larger compared to the V oc loss of ≈0.35 V for silicon, gallium arsenide, and perovskite solar cells. [16][17][18] Among all the photovoltaic parameters, the low V oc is evidently the one limiting the device performance of current CQD solar cells. Therefore, it's most urgent to explore an innovative passivation strategy to further reduce V oc loss and realize the breakthrough of CQD photovoltaic performance.After synthesis, most CQD surface trap states are generated during the ligand-exchange process, in which the insulating oleate ligands are replaced with short ones to facilitateThe high open-circuit voltage (V oc ) loss arising from insufficient surface passivation is the main factor that limits the efficiency of current lead sulfide colloidal quantum dots (PbS CQDs) solar cell. Here, synergistic passivation is performed in the direct synthesis of conductive PbS CQD inks by introducing multifunctional ligands to well coordinate the complicated CQDs surface with the thermodynamically optimal configuration. The improved passivation effect is intactly delivered to the final photovoltaic device, leading to an order lower surface trap density and beneficial doping behavior compared to the control sample. The obtained CQD inks show the highest photoluminescence quantum yield (PLQY) of 24% for all photovoltaic PbS CQD inks, which is more than twice the reported average PLQY value of ≈10%. As a result, a high V oc of 0.71 V and power conversion efficiency (PCE) of 13.3% is achieved, which results in the lowest V oc loss (0.35 eV) for the reported PbS CQD solar cells with PCE >10%, comparable to that of perovskite solar cells. This work provides valuable insights into the future CQDs passivation strategies and also demonstrates the great potential for the direct-synthesis protocol of PbS CQDs.

Breaking the Size Limitation of Directly‐Synthesized PbS Quantum Dot Inks Toward Efficient Short‐wavelength Infrared Optoelectronic Applications

“…And the reaction volume can be readily scaled to yield at least gram-scale quantities of QD solid in a one-pot synthesis with almost identical optical properties (Figure S10). The solar cell architecture is designed as ITO/ZnO/PbSinks/PbS-MPA/PBDB-T/MoOx/Ag according to the previous reports with some modifications (Figure 4a), [38,52,53] with the detailed fabrication process in the Supporting Information. The cross-section scanning electron microscope (SEM) image is shown in Figure S11.…”

“…[32][33][34][35] The indispensable ligand exchange step leads to numerous problems, including high material cost, complex processing, difficulty in scalable production and introduction of trap states, which certainly hamper their SWIR applications toward low-cost, civilian market. [36][37][38] Recently, we have designed a one-step, direct synthesis (DS) method to prepare low-cost semi-conducting PbS QD inks specifically for optoelectronic applications, where PbI 2 (lead source) react with N,N-Diphenyl thiourea (DPhTA) (sulfur source) to directly synthesize iodoplumbates-passivated QD inks (Figure 1a). [39][40][41] The obtained inks can be directly applied to fabricate optoelectronic devices without ligand-exchange processing.…”

Overcoming Charge Confinement in Perovskite Nanocrystal Solar Cells

“…[1][2][3][4][5] The power conversion efficiency (PCE) of PeQD solar cells has been increased to surpass those of other quantum-dot solar cells. [6][7][8] Furthermore, PeQDs are more photostable than polycrystalline perovskites; this trait is crucial for long-term stability of solar cells. [9] However, PeQD solar cells have lower record PCEs than that of polycrystalline perovskite solar cells.…”

High open-circuit voltage in lead sulfide quantum dot solar cells via solution-phase ligand exchange with low electron affinity cadmium halides

“…18,30 Direct synthesis of lead halide passivated PbS QDs also shows high potential to improve the V oc of QD solar cells. 39,40…”