Abstract:Colloidal quantum dot (CQD) solar
cells processed from pre-exchanged
lead sulfide (PbS) inks have received great attention in the development
of scalable and stable photovoltaic devices. However, the current
hole-transporting material (HTM) 1,2-ethanedithiol-treated PbS (PbS-EDT)
CQDs have several drawbacks in terms of commercialization, including
the need for oxidation and multilayer fabrication. Conjugated polymers
are an alternative HTM with adjustable properties. Here we propose
a series of conjugated poly… Show more
“…Furthermore, we increased the thickness of hybrid QD layers with the same control QD layers. The device having thicker hybrid QD layers exhibits decreased efficiency of 13.8% (Supplementary Table 1 ) that could have resulted from the unfavorable effects of CB solvent during upper hybrid layer deposition 46 , leading to PCBM exfoliation from CsPbI 3 QDs in the bottom layer. Fig.…”
All-inorganic CsPbI3 perovskite quantum dots have received substantial research interest for photovoltaic applications because of higher efficiency compared to solar cells using other quantum dots materials and the various exciting properties that perovskites have to offer. These quantum dot devices also exhibit good mechanical stability amongst various thin-film photovoltaic technologies. We demonstrate higher mechanical endurance of quantum dot films compared to bulk thin film and highlight the importance of further research on high-performance and flexible optoelectronic devices using nanoscale grains as an advantage. Specifically, we develop a hybrid interfacial architecture consisting of CsPbI3 quantum dot/PCBM heterojunction, enabling an energy cascade for efficient charge transfer and mechanical adhesion. The champion CsPbI3 quantum dot solar cell has an efficiency of 15.1% (stabilized power output of 14.61%), which is among the highest report to date. Building on this strategy, we further demonstrate a highest efficiency of 12.3% in flexible quantum dot photovoltaics.
“…Furthermore, we increased the thickness of hybrid QD layers with the same control QD layers. The device having thicker hybrid QD layers exhibits decreased efficiency of 13.8% (Supplementary Table 1 ) that could have resulted from the unfavorable effects of CB solvent during upper hybrid layer deposition 46 , leading to PCBM exfoliation from CsPbI 3 QDs in the bottom layer. Fig.…”
All-inorganic CsPbI3 perovskite quantum dots have received substantial research interest for photovoltaic applications because of higher efficiency compared to solar cells using other quantum dots materials and the various exciting properties that perovskites have to offer. These quantum dot devices also exhibit good mechanical stability amongst various thin-film photovoltaic technologies. We demonstrate higher mechanical endurance of quantum dot films compared to bulk thin film and highlight the importance of further research on high-performance and flexible optoelectronic devices using nanoscale grains as an advantage. Specifically, we develop a hybrid interfacial architecture consisting of CsPbI3 quantum dot/PCBM heterojunction, enabling an energy cascade for efficient charge transfer and mechanical adhesion. The champion CsPbI3 quantum dot solar cell has an efficiency of 15.1% (stabilized power output of 14.61%), which is among the highest report to date. Building on this strategy, we further demonstrate a highest efficiency of 12.3% in flexible quantum dot photovoltaics.
“…Recently, p‐type polymers such as TQ1, P3HT, PDTPBT, and PBDB‐TF have been explored as an alternative HTL to replace the EDT‐treated CQD layer, but these have failed to render high performance due to unfavorable energy level alignment. [ 12–15 ]…”
Colloidal quantum dot solar cells (CQD-SCs) are attractive in view of their wide optoelectronic tunability and manufacturing benefits. [1] The power conversion efficiency (PCE) of CQD-SCs has seen rapid advances over the past decade, reaching a PCE of 13.3% through improvements in CQD surface chemistry and device architecture. [2] To date, the most efficient CQD-SCs consist (Figure 1a) of a thin electron transport/hole-blocking layer of zinc oxide deposited on indium-tin-oxide; an active layer, comprising a CQD solid passivated using halide atoms; and a thin hole-transport layer (HTL) of CQDs cross-linked with 1,2-ethanedithiol (EDT). The EDTtreated CQD layer as the HTL provides well-optimized energy alignment and a desirable electric field distribution within the active layer. However, it also introduces drawbacks in view of its high density of trap states, [3] strong chemical interaction with the materials in the device stack, [4] and limited stability in encapsulated devices. [5] Importantly, it has a short diffusion length of tens of nm that precludes significant contribution to device photocurrent. [6] An ideal HTL in PbS CQD-SCs should combine appropriate energy levels to allow efficient hole-extraction and electronblocking; [7] sufficient hole mobility for efficient vertical charge transport; [8] a diffusion length enabling contribution to the device photocurrent; [9] materials processing that is compatible with underlying layers in the CQD device; [10] and excellent morphology and conformal coverage to prevent oxygen and moisture permeation. [11] Recently, p-type polymers such as TQ1, P3HT, PDTPBT, and PBDB-TF have been explored as an alternative HTL to replace the EDT-treated CQD layer, but these have failed to render high performance due to unfavorable energy level alignment. [12-15] Benzodithiophene (BDT)-based HTL (PTB7), an alternative to P3HT, has been introduced as a potential HTL in PbS CQD-SCs. The use of PTB7 led to increased PCE due to more suitable energy levels and relatively improved hole-mobility compared to P3HT. Yet, PTB7-based devices still exhibited a limited PCE of 9.6%, [8] significantly lower than of state-of-art CQDs-SC with a PCE of 13.3%, [2] due to low hole mobility of 10 −4 cm 2 V −1 s −1
“…In addition, the layer‐by‐layer deposition of the CQD‐EDT HTL prevents scalable fabrication of CQD‐SCs. [ 4 ]…”
Section: Introductionmentioning
confidence: 99%
“…As an alternative, polymeric p ‐type materials have been recently explored as a HTL in CQD‐SCs because of their single‐step solution processability, non‐toxic nature, and optoelectronic properties tunable through molecular design. [ 5–13 ] A power conversion efficiency (PCE) of 13.1% [ 14 ] was recently reported for CQD‐SCs using a polymer HTL, requiring further development to compete with CQD‐SCs based on the conventional CQD‐EDT HTL. [ 15 ]…”
of 4 based on the National Fire Protection Association (NFPA). In addition, the layer-by-layer deposition of the CQD-EDT HTL prevents scalable fabrication of CQD-SCs. [4] As an alternative, polymeric p-type materials have been recently explored as a HTL in CQD-SCs because of their single-step solution processability, nontoxic nature, and optoelectronic properties tunable through molecular design. [5-13] A power conversion efficiency (PCE) of 13.1% [14] was recently reported for CQD-SCs using a polymer HTL, requiring further development to compete with CQD-SCs based on the conventional CQD-EDT HTL. [15] The organic HTL is generally processed with a halogenated solvent, such as chlorobenzene (CB) (Figure 1a; MSDS hazard symbols: GHS07, GHS09). Halogen atoms are easily accumulated into the human body and ecosystems; thus, the substitution of toxic solvents is considered a priority for large-area fabrication and commercialization of CQD-SCs. [16] One candidate is 2-methylanisole (2-MA), a non-toxic food additive. [17,18] 2-MA shows higher polarity than CB, which suggests reengineering the polymer HTL for higher polarity. According to the like-dissolves-like principle, [19] this can be realized by breaking the symmetry of polymers. [20,21] A further potential benefit to this approach is the achievement of low crystallinity polymeric HTLs, an approach recently demonstrated to achieve high conductivity (by reducing grain boundaries) and thermal stability (by reducing lateral grain growth upon thermal stress). [22,23] Here, we design and synthesize random polymeric HTLs (asy-ranPBTBBDT) and compare them with control HTLs (asy-PBTBDT) having ethylhexyl branched alkyl chains (Figure 1b). The asy-ranPBTBBDT can be dissolved in various solvents owing to its extended branching points and random copolymerization. As a result, we demonstrate processing from 2-MA and report progress in both efficiency and thermal stability. The asy-ranPBTBDT-based CQD-SCs increase PCE to 13.2% while asy-BTBDT reference devices exhibit PCE 11.4% (Table S1, Supporting Information). The asy-ranPBTBDT CQD-SCs also improve operating stability, a finding we assign to the arresting of the process of lateral grain growth.
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