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The electron transport layer (ETL) is a critical component in perovskite quantum dot (PQD) solar cells, significantly impacting their photovoltaic performance and stability. Low-temperature ETL deposition methods are especially desirable for fabricating flexible solar cells on polymer substrates. Herein, we propose a room-temperature-processed tin oxide (SnO2) ETL preparation method for flexible PQD solar cells. The process involves synthesizing highly crystalline SnO2 nanocrystals stabilized with organic ligands, spin-coating their dispersion, followed by UV irradiation. The energy level of SnO2 is controlled by doping gallium ions to reduce the energy level mismatch with the PQD. The proposed ETL-based CsPbI3-PQD solar cell achieves a power conversion efficiency (PCE) of 12.70%, the highest PCE among reported flexible quantum dot solar cells, maintaining 94% of the initial PCE after 500 bending tests. Consequently, we demonstrate that a systemically designed ETL enhances the photovoltaic performance and mechanical stability of flexible optoelectronic devices. [ABSTRACT FROM AUTHOR]

Effective passivation of grain boundaries in perovskite solar cells is essential for achieving high device performance and stability. However, traditional polymer‐based passivation strategies can introduce challenges, including increased series resistance, disruption of charge transport, and insufficient passivation coverage. In this study, a novel approach is proposed that integrates a multifunctional ambipolar polymer into perovskite solar cells to address these issues. The ambipolar polymer is successfully incorporated into both the perovskite film and the hole transport layer (HTL), enabling comprehensive restoration of defect sites within the perovskite active layer. Moreover, this approach yields additional advantages for perovskite devices, such as enabling bidirectional charge transport, limiting pinhole formation at the HTL, reducing lithium‐ion migration from the HTL to the perovskite, and minimizing both the band offset and surface energy difference between the perovskite film and HTL interface. With these benefits, the ambipolar polymer integrated device achieves a power conversion efficiency (PCE) of 24.0%. Remarkably, it also exhibits enhanced long‐term stability, preserving 92% of its initial PCE after 2000 h under ambient conditions, and 80% of its initial PCE after 432 h under harsh conditions (at 85 °C and 85 ± 5% RH). [ABSTRACT FROM AUTHOR]

Despite recent advances in colloidal quantum dot (CQD) photovoltaics, several challenges persist and hinder further improvements. In particular, the Fermi level mismatch between the iodide‐treated photoactive and thiol‐treated hole‐transporting CQD layers creates an unfavorable energy band for hole collection. Furthermore, the numerous surface cracks in the thiol‐treated CQD layer facilitate direct contact between the photoactive CQD layer and the metal electrode, consequently leading to reduced device performance. To address these issues, a polycatechol functionalized MXene (PCA‐MXene) that can serve both as a dopant and an interlayer for CQD photovoltaics is developed. By achieving a uniformly dispersed mixture in a butylamine solvent, PCA‐MXene enables the effective combination of MXene and CQDs. This results in the modification of the work function of CQDs and the modulation of the energy band alignment, ultimately promoting enhanced hole extraction. Moreover, the PCA‐MXene employed as an interlayer effectively covers the surface cracks present in the thiol‐treated CQD layer. This coverage inhibits both metal electrode penetration and moisture intrusion into the device. Owing to these advantages, the CQD photovoltaics incorporating PCA‐MXene achieve a power conversion efficiency (PCE) of 13.6%, accompanied by enhanced thermal stability, in comparison to the reference device with a PCE of 12.8%. [ABSTRACT FROM AUTHOR]

For efficient colloidal quantum dot (CQD) solar cells (CQD‐SCs), thiol‐passivated p‐type CQDs are generally used as a hole‐transporting material (HTM); however, there are issues with the control of optoelectrical properties, low thiol passivation rate, and poor morphology with a power conversion efficiency (PCE) of approximately 11%. Although polymeric HTMs have been introduced to address these issues, maximizing efficiency and achieving green‐solvent processability and thermal stability for commercialization is necessary. Here, we synthesize a novel benzodifuran (BDF)‐based HTM (asy‐ranPBTBDF) showing an electron‐deficient state, low steric hindrance, and low planarity compared to those of a typical benzodithiophene (BDT)‐based HTM (asy‐ranPBTBDT). BDF properties lead to deep high occupied molecular orbital (HOMO) levels, close π–π stacking, excellent solubility, and amorphous properties related to efficiency, green‐solvent processability, and thermal stability. With these benefits, the asy‐ranPBTBDF‐based CQD‐SC showed enhanced open‐circuit voltage (VOC) (0.65 V) and PCE (13.29%) compared to those of the asy‐ranPBTBDT‐based device (0.63 V and 12.22%) in toxic processes with chlorobenzene. The asy‐ranPBTBDF‐based CQD‐SC showed a PCE of 12.51% in a green‐solvent process with 2‐methylanisole and improved thermal stability at 80 °C (83.8% retaining after 24 h) owing to less lateral crystallization than the asy‐ranPBTBDT‐based device (60.8% retaining after 24 h). [ABSTRACT FROM AUTHOR]

The ligand exchange procedure of CsPbI3 perovskite quantum dots (PQDs) enables the fabrication of thick and conductive PQD solids that act as a photovoltaic absorber for solution‐processed thin‐film solar cells. However, the ligand‐exchanged CsPbI3 PQD solids suffer from deterioration in photovoltaic performance and ambient stability due to the surface traps, such as uncoordinated Pb2+ sites on the PQD surface, which are generated after the conventional ligand exchange process using ionic short‐chain ligands dissolved in polar solvents. Herein, a facile surface stabilization is demonstrated that can simultaneously improve the photovoltaic performance and ambient stability of CsPbI3 PQD photovoltaic absorber using covalent short‐chain triphenylphosphine oxide (TPPO) ligands dissolved in a nonpolar solvent. It is found that the TPPO ligand can be covalently bound to uncoordinated Pb2+ sites and the nonpolar solvent octane can completely preserve the PQD surface components. Owing to their synergetic effects, the CsPbI3 PQD photovoltaic absorber stabilized using the TPPO ligand solution dissolved in octane exhibit higher optoelectrical properties and ambient stability than the control absorber. Consequently, CsPbI3 PQD solar cells composed of PQD photovoltaic absorbers fabricated via surface stabilization strategy provide an improved power conversion efficiency of 15.4% and an enhanced device stability. [ABSTRACT FROM AUTHOR]

The hole transport layer (HTL) plays a key role in inverted perovskite solar cells (PSCs), and nickel oxide has been widely adopted for HTL. However, a conventional solution‐processed bottom‐up approach for NiOx (S‐NiO) HTL fabrication shows several drawbacks, such as poor coverage, irregular film thickness, numerous defect sites, and inefficient hole extraction from the perovskite layer. To address these issues, herein, a novel NiOx HTL top‐down synthesis route via electrochemical anodization is developed. The basicity of the electrolyte used in anodization considerably influences electrochemical reactions and results in the structure of the anodized NiOx (A‐NiO). The optimized A‐NiO provides outstanding optoelectrical properties, including uniform film thickness, enhanced transmittance, deep‐lying valance band, low trap density, and better hole extraction ability from the perovskite. Owing to these advantages, the A‐NiO‐based inverted PSC exhibits an improved power conversion efficiency of 21.9% compared with 19.1% for the S‐NiO‐based device. In addition, the A‐NiO device shows a higher inlet and long‐term ambient stability than the S‐NiO device due to the superior hole transfer ability of A‐NiO, which suppresses charge accumulation between NiOx and the perovskite interface. [ABSTRACT FROM AUTHOR]

Highlights: We designed and developed a 3D star-shaped conjugated molecule (Star-TrCN) to incorporate organic semiconductor with CsPbI3 perovskite quantum dots (PQDs). The robust chemical bonding of Star-TrCN and PQDs is demonstrated by theoretical modeling and experimental validation, which significantly improved the cubic-phase stability of CsPbI3-PQDs by passivating vacant sites and preventing moisture penetration. The Star-PQD hybrid solar cells not only achieved remarkable device stability over 1000 h at 20–30% relative humidity, but also boosted power conversion efficiency up to 16.0% via cascade energy band structure. Perovskite quantum dots (PQDs) have been considered promising and effective photovoltaic absorber due to their superior optoelectronic properties and inherent material merits combining perovskites and QDs. However, they exhibit low moisture stability at room humidity (20–30%) owing to many surface defect sites generated by inefficient ligand exchange process. These surface traps must be re-passivated to improve both charge transport ability and moisture stability. To address this issue, PQD-organic semiconductor hybrid solar cells with suitable electrical properties and functional groups might dramatically improve the charge extraction and defect passivation. Conventional organic semiconductors are typically low-dimensional (1D and 2D) and prone to excessive self-aggregation, which limits chemical interaction with PQDs. In this work, we designed a new 3D star-shaped semiconducting material (Star-TrCN) to enhance the compatibility with PQDs. The robust bonding with Star-TrCN and PQDs is demonstrated by theoretical modeling and experimental validation. The Star-TrCN-PQD hybrid films show improved cubic-phase stability of CsPbI3-PQDs via reduced surface trap states and suppressed moisture penetration. As a result, the resultant devices not only achieve remarkable device stability over 1000 h at 20–30% relative humidity, but also boost power conversion efficiency up to 16.0% via forming a cascade energy band structure. [ABSTRACT FROM AUTHOR]

Summary: Ternary silver bismuth sulfide (AgBiS2) colloidal nanocrystals (NCs) have been recognized as a photovoltaic absorber for environmentally‐friendly and low‐temperature‐processed thin film solar cells. However, previous synthetic methods involving hot injection of sulfur precursors into metal oleate precursor solutions do not provide a balance between nucleation and growth, leading to AgBiS2 NCs with broad size distributions. Here, we demonstrate the modified synthetic route that size distribution of AgBiS2 NCs can be improved by pre‐adding the non‐coordinating 1‐octadecene (ODE) solvent into metal precursor solutions, leading to controlled concentration of coordinating oleic acid with improved hot‐injection synthetic conditions. The addition of ODE as a non‐coordinating solvent to metal precursor/oleic acid solution significantly suppresses variations in the concentration of coordinating oleic acid after injection of the sulfur precursor solution, leading to a homogenous reaction between the metal and sulfur precursors. For photovoltaic devices fabricated using the resultant AgBiS2 NCs, the champion device shows power conversion efficiency (PCE) of 5.94% with an open‐circuit voltage (VOC) of 0.52 V. This performance is better than that a control device (PCE of 5.50% and VOC of 0.49 V) because of the reduced energetic disorder and band tail broadening originating from the uniformly‐sized AgBiS2 NCs. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs) are considered as next-generation semiconductors owing to their tunable optical and electrical properties depending on their particle size and shape. The characteristics of CQDs are mainly governed by their surface chemistry, and the ligand exchange process plays a crucial role in determining their surface states. Worldwide studies toward the realization of high-quality quantum dots have led to advances in ligand exchange methods, and these procedures are usually carried out in either solid-state or solution-phase. In this article, we review recent advances in solid-state and solution-phase ligand exchange processes that enhance the performance and stability of lead sulfide (PbS) CQD solar cells, including infrared (IR) CQD photovoltaics. [ABSTRACT FROM AUTHOR]

Advances in surface chemistry and manipulation of fully inorganic CsPbI 3 perovskite quantum dots (CsPbI 3 -QDs) have enabled improving the charge transport and photovoltaic performance of CsPbI 3 -QD thin films by replacing their native long-chain, insulating ligands with short-chain ligands. However, the conventional approach based on formamidinium (FA) replacement removes the hydrophobic protective layer, opening the path for moisture penetration and resulting in poor device stability. We demonstrate that short-chain and hydrophobic phenethylammonium (PEA) cations, instead of FA, are efficiently incorporated only onto CsPbI 3 -QD surfaces, confirmed by Fourier-transform infrared, H nuclear magnetic resonance and density functional theory calculations. PEA incorporation leads simultaneously to improved photovoltaic performance and moisture stability of resultant CsPbI 3 -QDs without any change in size, fully inorganic composition, and dimensionality of CsPbI 3 -QDs. Therefore, PEA-incorporated CsPbI 3 -QD solar cells show a high device power conversion efficiency of 14.1% and high moisture stability, retaining over 90% of the initial performance after 15 days under ambient conditions. Aromatic ring-based phenethylammonium is incorporated into CsPbI 3 quantum dots (CsPbI 3 -QDs) by removing their native and insulating oleylammonium ligands. This approach simultaneously improves photovoltaic performance and cubic-phase stability of CsPbI 3 -QD solids under ambient moisture conditions up to 15 days. Thus, CsPbI 3 -QD solar cells show efficient device performance of 14.1% power conversion efficiency with improved device ambient stability. Image 1 • Long-chain, insulating OLA ligands of CsPbI 3 -QDs are exchanged to short-chain, hydrophobic PEA cations. • This strategy enables improved both charge transport and moisture stability of CsPbI 3 -QDs. • PEA incorporations show no changes in size, composition and dimensionality of fully inorganic CsPbI 3 -QDs. • PEA-incorporated CsPbI 3 -QD solar cells show improved device performance up to 14.1% PCE. • Initial PCE of PEA-incorporated CsPbI 3 -QD solar cells retained over 90% for 15 days under ambient conditions. [ABSTRACT FROM AUTHOR]

Fully inorganic CsPbI 3 perovskite quantum dots (CsPbI 3 -PQDs) are known as the best-performing photovoltaic absorber in colloidal quantum dot solar cells. This is achieved by improving the cubic-phase-stabilization and electronic-coupling in CsPbI 3 -PQD solids. In conventional approaches, the hydrolysis of methyl acetate (MeOAc) resulting in acetic acid and methanol as intermediate substances plays a key role in replacing long-chain hydrocarbons with short-chain ligands, which improves charge transport in the CsPbI 3 -PQD solids. However, CsPbI 3 -PQDs suffer from lattice distortion and instability under acidic conditions including protons and polar media, leading to CsPbI 3 -PQD fusion and poor photovoltaic performance. Herein, we report that electronic coupling and photovoltaic performance of CsPbI 3 -PQD solids are improved by efficient removal of long-chain oleate ligands using a solution of sodium acetate (NaOAc) in MeOAc, which results in the direct generation of OAc ions without forming protons and methanol. NaOAc-based ligand exchange of CsPbI 3 -PQDs enables preservation of their nanocrystal size without fusion and minimization of surface trap states originating from metal hydroxide formation on their surfaces. Consequently, the best solar cell comprising NaOAc-treated CsPbI 3 -PQDs shows an improved device performance with a power conversion efficiency (PCE) of 13.3%, as compared with a lead nitrate-treated control device (12.4% PCE). We demonstrate that sodium acetate (NaOAc) directly generates short-chain OAc ions to exchange the long-chain oleate ligands of CsPbI 3 perovskite quantum dots (CsPbI 3 -PQDs). NaOAc-based ligand exchange enables preservation of CsPbI 3 -PQD size, minimization of surface trap states, and enhancement of electronic coupling in the resultant CsPbI 3 -PQD solids. Consequently, NaOAc-treated CsPbI 3 -PQD solar cells show improved device performance with 12.4% power conversion efficiency. Image 1 • NaOAc directly generates short-chain OAc ions to exchange the oleate ligands of CsPbI 3 -PQDs. • Our strategy enables minimizing the formation of protons and methanol during the ligand exchange. • NaOAc-based ligand exchange enables preserving nanocrystal size and minimizing surface traps. • Resultant CsPbI 3 -PQD solids show enhanced electronic coupling with improved charge transport. • NaOAc-treated CsPbI 3 -PQD solar cells show improved photovoltaic performance up to 13.33% PCE. [ABSTRACT FROM AUTHOR]

• A versatile ThMAI-treatment for conductive and stable PQD solids. • Multifaceted anchoring of ThMAI improves surface passivation. • Strong ThMAI binding restores tensile strain and stability of black phase PQDs. • ThMAI-treatment improves solar cell performance (15.3%) and enhances stability. All-inorganic CsPbI 3 perovskite quantum dots (PQDs) hold significant potential for next-generation photovoltaics due to their unique optoelectronic properties, and the surface-bound ligand playing a key role in the stability and functionality of CsPbI 3 PQDs. Initially used long-chain ligands in PQDs synthesis stabilize the black phase but hinder charge transport when employed to solar cells, necessitating their replacement with shorter ones. However, this leads to the formation of surface defects and loss of tensile strain, resulting in the transition to the undesired orthorhombic phase (δ-phase) and compromising PQD solar cell performance. Therefore, developing a ligand exchange process that achieves the optimal balance between conductivity and stability in PQD solid films continues to be a significant challenge. To address these issues, we developed an efficient ligand-exchange process utilizing a multifaceted anchoring ligand, 2-thiophenemethylammonium iodide (ThMAI). The larger ionic size of ThMA+ compared to Cs+ facilitates the restoration of surface tensile strain in PQDs, while its thiophene and ammonium groups enable effective passivation of surface defects. Owing to these advantages, ThMAI-treated CsPbI 3 PQD thin films exhibit improved carrier lifetime, uniform PQD orientation, and increased ambient stability. As a result, the ThMAI-treated CsPbI 3 PQD solar cells demonstrate an improved power conversion efficiency (PCE) of 15.3 % and an enhanced device stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • CsPbI 3 -PQDs have high potential as semi-transparent PV absorbers. • DMD electrodes deliver superior PV performance of semi-transparent PQD solar cells. • asym -MAM stacks show higher optical transmittance than sym -MAM stacks. • Optical simulation confirms asym -MAM stacks reduce the parasitic absorption loss. • Semi-transparent PQD solar cells show a PCE of 11.3% with an AVT of 23.4%. CsPbI 3 perovskite quantum dots (CsPbI 3 -PQDs) have a high potential as semi-transparent photovoltaic absorbers because of the facile control of film thicknesses, size-tunable optical band gaps, and nanometer-scale grain sizes suppressing light scattering. Conventional semi-transparent CsPbI 3 -PQD solar cells showed low photovoltaic performances due to the low electrical conductivity of the graphene electrodes. Here we report that dielectric/ultra-thin metal/dielectric (DMD) electrodes with excellent optical transmittance and electrical conductivity deliver superior photovoltaic performances in the semi-transparent CsPbI 3 -PQD solar cells. Particularly, the asymmetric DMD electrodes composed of MoO x 15 nm/Au 10 nm/MoO x 35 nm (asym -MAM) stacks exhibit higher optical transmittance than that of the symmetric MoO x 15 nm/Au 10 nm/MoO x 15 nm (sym -MAM) stacks. The optical simulation confirms that asym -MAM stacks reduce the parasitic absorption loss in metal interlayers. Therefore, the asym -MAM stacks with a high electrical conductivity show a higher average visible transmittance (AVT) than that of the sym -MAM. Consequently, the semi-transparent CsPbI 3 -PQD solar cells fabricated using the asym -MAM transparent top electrodes show a power conversion efficiency of 11.3% with a considerable AVT values of 23.4% (400–800 nm) and 20.0% (380–780 nm), respectively, which were calculated from their transmittance spectra. This is the highest-efficiency semi-transparent PQD solar cells that can be used for solar window applications requiring an AVT value of over 20%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Conductive and thick PQD PV absorbers are fabricated via single-step process. • PEAOAc results in replacing both OLE and OAM ligands of PQDs with PEA and OAc. • SPLE using PEAI reduces the long-chain ligands and improves surface passivation. • Single-step-fabricated CsPbI 3 -PQD solar cells show improved PCE of 13.7%. • Single-step process is advantageous for roll-to-roll suitable to mass production. Lead halide perovskite colloidal quantum dots (PQDs) are receiving great interest in emerging photovoltaics because of their excellent photovoltaic properties and the room-temperature processability without a thermal annealing step. Conductive thick PQD absorbers reported to date have been fabricated via multiple-step layer-by-layer deposition based on solid-state ligand exchange; however, this approach requiring a lot of processing time and cost is not suitable for the mass production. Thus, a single-step fabrication approach of conductive thick PQD absorbers should be devised. Herein, we demonstrate that conductive thick CsPbI 3 -PQD absorbers can be fabricated via a single-step process based on the surface ligand manipulation and employed in efficient PQD solar cells. We find that the conventional ethyl acetate-based post-treatment significantly removes long-chain ligands of the unexchanged PQDs (UN-PQDs) and cause film delamination of thick UN-PQD solids because of drastic volume shrinkage. Thus, we employ the methyl acetate-based post-treatment using phenethylammonium acetate (PEAOAc) to replace both long-chain oleate and oleylammonium within thick UN-PQD solids with short-chain PEA and OAc ligands without film delamination. To further reduce long-chain ligands within the resultant PQD solids, we also employ the PQDs prepared via a solution-phase ligand exchange (SPLE-PQDs) using the phenethylammonium iodide. Furthermore, we perform various spectroscopic measurements, including Fourier-transform infrared, nuclear magnetic resonance, and X-ray photoelectron spectroscopy, to quantitatively analyze the surface chemistry and ligands of PQDs. Consequently, CsPbI 3 -PQD solar cells, fabricated via a single-step process using SPLE-PQDs and PEAOAc post-treatment, show improved power conversion efficiency (13.7%) compared to that of the UN-PQD device (12.1%). [ABSTRACT FROM AUTHOR]