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

Section: Degradation Of Charge Extraction Layers In Solar Cellsmentioning

confidence: 99%

Stability of Quantum Dot Solar Cells: A Matter of (Life)Time

Albaladejo‐Siguan

Baird

Becker‐Koch

et al. 2021

“…[18,24] The series of polymers were prepared using microwave-assisted Stille coupling polymerization (Scheme S1 and Figure S1a, Supporting Information). Chemical structures of molecules were obtained using 1 H-NMR, 13 C-NMR, and elemental analysis (EA) ( Figures S2-S5, Supporting Information). The number-average molecular weight (M n ) and polydispersity (PDI), which are characterized via gel-permission chromatography with chlorobenzene (CB) at 40 °C and calibration curves of polystyrene standards are M n = 13 and 26 kDa with PDI = 2.0 and 2.4 for asy-PBTBDT and asy-ranPBTBBDT, respectively (Figure 2a).…”

Section: Resultsmentioning

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 ]…”

Section: Introductionmentioning

confidence: 99%

Efficient and Stable Colloidal Quantum Dot Solar Cells with a Green‐Solvent Hole‐Transport Layer

Kim

Lee

Choi

et al. 2020

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.

“…[180,182,183] Recently, Jang and coworkers designed a type of organic π-conjugated polymer, PBDTTPD-HT, as HTL for QD solar cells and proved a device PCE of 11.53%. [184] Park and coworkers developed a new random polymeric HTL, asy-ran PBTBDT, and fabricated PbS QD solar cells showing a PCE of 13.2%. [185] In addition, there are a few other noteworthy device engineering strategies.…”

Section: Device Structure Engineeringmentioning

confidence: 99%

Quantum Dots for Photovoltaics: A Tale of Two Materials

Duan

Guan

et al. 2021

solar cells (PSCs), and colloidal quantum dots (QDs) solar cells, have been quickly developed. [3][4][5][6][7][8][9][10][11] Among these diverse PV materials, QDs possess unique nanostructural uniformity and highly tunable features, including quantum confinement effects and multiple exciton generation (MEG). [12][13][14][15][16][17] QD solar cells can be fabricated as semitransparent and flexible for promising applications, such as, wearable energy collectors and building-integrated photovoltaics. [18,19] QDs are defined as nanometer-sized semiconducting crystals, usually chemically synthesized with surface ligands. [20,21] When the size of a semiconducting crystal reduces to the molecular scale, its bulk properties alter simultaneously. [22,23] Owing to the quantum confinement effect, the absorption spectra and energy levels of QDs can be easily tuned by size variation. For example, the bandgap of cadmium telluride (CdTe) bulk material is around 1.48 eV, while the bandgap of the CdTe QD can be tuned from 2.06 to 2.32 eV by a slight size reduction from 2.47 to 2.10 nm. [24,25] The quantum confinement effect also allows better energy level and absorption matching for QD-based optoelectronic devices such as photodetectors, light-emitting diodes, and solar cells. [26][27][28][29][30][31][32][33][34] Additionally, QDs enable hot cattier extraction due to the MEG effect, where one absorbed photon with high energy may generate two or more excitons. [27,35,36] The unique capability of MEG in QD solar cells can potentially improve the power conversion efficiency (PCE) of single-junction devices and thus overcome the Shockley-Queisser (SQ) PCE limit. [37][38][39] In the past decades, increasing research attention has been paid to QD solar cells, and many materials have been exploited in this context. Although there have been some trials on leadfree materials, such as Indium arsenide (InAs), InP, and AgBiS 2 , their device performances are still poor, with PCE less than 6%. [40][41][42][43][44][45] Up to now, most of the high-performance devices were reported from lead-based QDs in two main categories: lead chalcogenides (PbX, X = S, Se) and lead halide perovskites (PVK). Figure 1a depicts the progress in PCE values and accumulated publication numbers of lead-based QD solar cells, shown as points and columns, respectively, since 2010. With recent progress in device structure design, band-alignment engineering, and optimized surface passivation, the PCE of QD solar cells has constantly increased, achieving a record of 16.6% to date. [46][47][48] Before 2016, QD solar cells were mainly composed of PbX (X = S, Se), and continuous efforts have recently culminated in a remarkable PCE of 13.8%. [53][54][55] PbX usually crystallizes in a cubic structure with S or Se atoms located at octahedral Quantum dot (QD) solar cells, benefiting from unique quantum confinement effects and multiple exciton generation, have attracted great research attention in the past decades. Before 2016, research efforts were mainly devoted to solar cells ...