awn

Metal grids are reviewed based on their application in perovskite solar cells. The choices of materials, design, deposition technique, trade-off between electrical conductivity versus optical transmission, among other features, are discussed in conjunction with perovskite particularities. A patent analysis is also discussed, along with perspectives for the commercialization of large-area perovskite solar cells and modules.

Lab-scale perovskite solar cells have reached efficiencies as high as the best monocrystalline silicon cells, with expectations that their manufacturing costs could be lower than those of currently commercialized cells. As a result, efforts are now directed to the production of these cells. In this sense, the use of frontal metal grids in large-area perovskite cells and parallel-connected modules is imperative due to the low conductivity of the transparent conductive substrate usually employed in these devices. For the insertion of grids, a trade-off between reduced resistive losses and the increase in shadowed area must be achieved. Assessment of grid parameters is of utmost importance for the assembly of viable large-scale cells and modules. Furthermore, a direct transfer from grid parameters previously specified for other photovoltaic technologies might not be the best option for perovskite cells. Nonetheless, investigations of grids specifically designed for these cells are still scarce in the literature. Here, grid design, both in terms of metal composition and geometric factors, is discussed, including their development for tandem cells and flexible devices. To provide further insights into the maturity level of this technology, a patent analysis regarding grid designs for perovskite modules is also presented in this review.

A poly(methyl methacrylate) (PMMA) interlayer between the perovskite and CuPc improves the insufficient electron blocking due to the low LUMO energy level of CuPc. In addition, the PMMA layer strongly interacts with the perovskite, greatly reducing the defect density responsible for non-radiative recombination. Eventually, PMMA significantly improves the efficiency of PSCs fabricated using CuPc as a hole conductor.

Abstract

The use of inexpensive, highly efficient, and long-term stable hole-transporting layers (HTLs) while facilitating the fabrication process has become a critical issue for PSC commercialization. Among organic HTLs, copper phthalocyanine (CuPc) has been increasingly studied owing to its low cost and excellent thermal stability. Nevertheless, CuPc has a low energy level in the conduction band, resulting in low efficiency due to a poor electron barrier. In this study, an efficient and stable PSC is fabricated by combining CuPc with an ultrathin poly(methyl methacrylate) (PMMA) interlayer, which is deposited on a [(FAPbI₃)_0.95(MAPbBr₃)_0.05] absorption layer (here, FAPbI₃ and MAPbBr₃ denote formamidinium lead triiodide and methylammonium lead tribromide, respectively). PMMA in perovskite has been found to reduce perovskite surface defects and series resistance as well as the electronic barrier to HTL. The optimum concentration of PMMA allows for the fabrication of the PSC with a PCE of 21.3%, which is the highest PCE for PSCs featuring metal phthalocyanines as the HTL reported to date. The stability of the encapsulated PSC exceeds 80% after 760 h at 85 °C under 85% RH conditions.

Hydride vapor phase epitaxy (HPVE) is a promising growth technique for reducing the fabrication cost of III–V devices. The improvement in the solar cell performance by introducing AlInGaP back-surface field layers is reported. Consequently, 28.3% efficient InGaP/GaAs tandem solar cells, the highest conversion efficiency reported in cells grown via HPVE, is achieved.

Hydride vapor phase epitaxy (HVPE) is a III–V device fabrication technology that has received attention owing to its low production costs. The properties of passivation layers used to reduce surface and interface recombination losses in III–V materials considerably contribute to the performance of various devices. Herein, solar cells based on AlInGaP back-surface field (BSF) layers grown via HVPE using aluminum trichloride as the group-III precursor for Al deposition are presented. Although high-concentration Si contamination occurs in Al-containing layers grown using HVPE, AlInGaP with p-type conductivity can be grown by doping with high-concentration Zn. For InGaP single-junction solar cells, the short-circuit current density and open-circuit voltage are improved by introducing the AlInGaP BSF layer. Consequently, the InGaP single-junction solar cells measured under air mass 1.5 global solar spectrum illumination achieve a conversion efficiency of 17.1%. Furthermore, the progress in the development of tandem solar cells grown using HVPE is reported. By improving the performance of the InGaP top cells, InGaP/GaAs tandem cells are fabricated with a new record efficiency of 28.3% using the triple-chamber HVPE system.

Publication date: March 2022

Source: Nano Energy, Volume 93

Author(s): Jianhua Jing, Sheng Dong, Kai Zhang, Boming Xie, Jiabin Zhang, Yu Song, Fei Huang

Flexible Photovoltaic Devices

In article number 2100733, Sang Hyuk Im and co-workers developed super flexible transparent conducting oxide (TCO)-free perovskite solar cells with a single-layered graphene electrode on polydimethylsiloxane substrates with excellent bending stability. By co-doping the graphene/PTAA layers with varying concentrations of Li-TFSI additives, the optoelectronic properties of the TCO-free electrode could be manipulated to optimize charge collection for highly efficient and flexible photovoltaic devices.

For the first time, a certified fill factor value of 79% is obtained for hole selective layer-free carbon-based perovskite solar devices. The influence of charge recombination and transport losses is assessed. An optimized saturated vapor crystallization in the mesoscopic stack allows for minimized losses, leading to a better interface formation between the perovskite and the adjacent interfaces.

Carbon-electrode-based perovskite solar cells (C-PSCs) are promising candidates for commercialization due to their high stability. However, the absence of a hole selective layer (HSL) often limits their performance, yielding low fill factors (FFs). Herein, a certified FF of 78.8% obtained through HSL-free C-PSCs is focused. This is found to approach the highest values reported for metal-electrode-based PSCs employing highly selective HSLs. The loss mechanisms affecting the FF in fully printed HSL-free C-PSCs are thus investigated. Methods commonly used to analyze and quantify the impact of recombination and transport losses on the FF of established photovoltage devices are assessed, and their applicability in C-PSCs is examined. In the improved devices, non-radiative recombination contributes to only 3%_abs loss with respect to the FF in the radiative limit, which is attributed to an optimal diode ideality factor approaching 1.0. Moreover, contributions of shunt resistive losses are determined to be negligible. Interfacial series resistance losses at the perovskite/carbon interface are identified as the main loss channel, highlighting the importance of the quality of the contact between the perovskite and the back-contact electrode.

A room temperature solid-state ligand exchange method modified tantalum-doped tin oxide (Ta-SnO₂) with a functional ligand, enhancing the conductivity of Ta-SnO₂ and improving the band alignment with the electrode is reported. Furthermore, the efficiency of fullerene-free devices can achieve up to 15.48%. All-oxide devices can maintain 80% performance after 1000 and 540 h under damp heat and light soaking tests.

Although perovskite solar cells (PSCs) can be prepared with excellent optoelectronic properties and solution processability, the common use of [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) as the electron-transporting layer (ETL), with its high cost and low stability, has hindered their commercialization. Metal oxides are inexpensive and highly chemically stable, making them potential alternatives to PCBM as ETLs, but requisite polar host solvents and high-temperature treatment limit the possibility of their direct deposition on perovskite layers. Herein, Ta-doped SnO₂ nanoparticles (NPs) are dispersed in a nonpolar solvent and they are also directly deposited to form a Ta-SnO₂ layer on a perovskite film. Then, room-temperature solid-state ligand exchange is applied to remove insulating molecules from the Ta-SnO₂ surface and thereby, enhance the band alignment between the Ta-SnO₂ layer and the Ag electrode. The highest power conversion efficiency of a PSC fabricated with Ta-SnO₂ as the ETL is 15.48%. In addition, the stability of the SnO₂-based devices toward damp heat and light soaking is superior to that of corresponding PCBM-based PSCs. Therefore, this effective strategy for incorporating metal oxides as ETLs appears to be an inexpensive method for manufacturing highly efficient PSCs with long-term stability.

A facile method is reported to passivate the SnO₂/perovskite interface and neutralize OH⁻ on the SnO₂ surface by modifying the SnO₂/pervoskite interface with phosphorus-containing Lewis acids. The power conversion efficiency of the optimal device is increased from 18.94% to 22.14%, along with negligible hysteresis. Meanwhile, the corresponding solar modules also achieved a champion efficiency of 15.69% with excellent stability under continuous illumination.

Expeditious charge transfer at the interfaces between photoactive and charge transport layers is critical in perovskite solar cells (PSCs). Defects on the surface of charge transport layers usually lead to the degradation of carrier mobility, resulting in low power conversion efficiency (PCE) and serious hysteresis. Herein, phosphorus-containing Lewis acids are applied to modify the SnO₂/perovskite interface and neutralize redundant OH⁻ on the SnO₂ surface. The interaction between the Lewis acids and SnO₂ significantly accelerate the electron transfer and greatly reduce the energy barrier at the SnO₂/perovskite interface, boosting the PCE of the PSCs. By modifying the SnO₂/pervoskite interface with diphenylphosphine oxide, the PCE of a small area device was increased from 18.94% to 22.14%, along with negligible hysteresis and improved stability. Moreover, the 5 × 5 cm² solar modules with an aperture area of 22.56 cm² achieved a best efficiency of 15.69%.

A new design strategy for exploring colloidal quantum dot (CQD)/polymer interfaces is proposed: an additional interfacial layer is incorporated between the CQD/polymer bilayer structures. The interfacial layer between CQD and polymer reduces the localized charge accumulation, suppressing bimolecular recombination. The optimized hybrid devices show a maximum power conversion efficiency of 13.74% and retains over 90% of its initial performance for 402 days under ambient condition without any treatment.

Abstract

Emerging semiconducting materials including colloidal quantum dots (CQDs) and organic molecules have unique photovoltaic properties, and their hybridization can result in synergistic effects for high performance. For realizing the full potential of CQD/organic hybrid devices, controlling interfacial properties between the CQD and organic matter is crucial. Here, the electronic band between the CQD and the polymer layers is carefully modulated by inserting an interfacial layer treated with several types of ligands. The interfacial layer provides a cascading conduction band offset (ΔE _C), and reduces local charge accumulation at CQD/polymer interfaces, thereby suppressing bimolecular recombination; a thin thiol-treated interfacial layer (≈6 nm) decreases shallow traps, resulting in higher short-circuit current (J _SC) and fill factor of hybrid solar cells. Based on these results, a high performance CQD/polymer hybrid solar cell is introduced that demonstrates a power conversion efficiency of 13.74% under AM 1.5 solar illumination. The hybrid device retains more than 90% of its initial performance after 402 days under ambient conditions.

Herein, a low-dimensional intermediate-assisted growth (LDIAG) method is reported to deposit high quality CsPbI₂Br film in ambient atmosphere by introducing imidazolium halide to control both nucleation and growth kinetics. The obtained CsPbI₂Br solar cell shows an efficiency of 17.26% and excellent long-term stability with ≈86% of its initial efficiency retained after being exposed to the ambient environment for 1000 h.

Abstract

Inorganic CsPbI₂Br perovskite is promising for solar cell applications due to its excellent thermal stability and optoelectronic characteristics. Unfortunately, the current high-efficiency CsPbI₂Br perovskite solar cells (PSCs) are mostly fabricated in an inert atmosphere due to their instability to moisture. Herein, a low-dimensional intermediate-assisted growth (LDIAG) method is reported for the deposition of CsPbI₂Br film in ambient atmosphere by introducing imidazole halide (IMX: IMI and IMBr) into the precursor solution to control both nucleation and growth kinetics. The IMX first combines with PbI₂ in the precursor film to form a 2D intermediate which then gradually releases PbI₂ to slowly form high-quality CsPbI₂Br film during annealing. It is found that the LDIAG method produces a uniform, highly crystalline, pinhole-free, and stable CsPbI₂Br film with low defect density. Consequently, the solar cell efficiency is increased to as high as 17.26%, one of the highest for this type of device. Furthermore, the bare device without any encapsulation shows excellent long-term stability with ≈86% of its initial efficiency retained after being exposed to the ambient environment for 1000 h. This work provides a perspective to tune the intermediate phases and crystallization pathway for high-performance inorganic PSCs formed under ambient conditions.

The relationship between intermolecular electron–phonon coupling and trapping of electronic excitation behind kinetic aggregation of nonfullerene acceptors (NFAs) is revealed in multicomponent organic solar cells (OSCs). The synergistic regulation of donor and acceptor materials can prevent unfavorable aggregation of NFAs, maintaining stable intermolecular electron-phonon coupling to suppress the increase of trap depth and density for photocarrier trapping in quaternary OSCs.

Abstract

The kinetic aggregation of nonfullerene acceptors under nonequilibrium conditions can induce electron–phonon interaction roll-off and electronic band structure transition, which represents an important limitation for long-term operational stability of organic solar cells (OSCs). However, the fundamental underlying mechanisms have received limited attention. Herein, a photophysical correlation picture between intermolecular electron–phonon coupling and trapping of electronic excitation is proposed based on the different aggregation behaviors of BTP-eC9 in bulk-heterojunction and layer-by-layer processed multicomponent OSCs. Two separate factors rationalize their correlation mechanisms: 1) the local lattice and/or molecular deformation can be regarded as the results of BTP-eC9 aggregates in binary system under continuous heating, which brings about attenuated intermolecular electron–phonon coupling with intensified photocarrier trapping. 2) The higher density of trap states with more extended tails into the bandgap give rise to the formation of highly localized trapped polarons with a longer lifetime. The stabilized intermolecular electron–phonon coupling through synergistic regulation of donor and acceptor materials effectively suppresses unfavorable photocarrier trapping, delivering the improved device efficiency of 18.10% and enhanced thermal stability in quaternary OSCs. These results provide valuable property–function insights for further boosting photovoltaic stability in view of modulating intermolecular electron–phonon coupling.

This study reports on novel solution-processed fullerene derivatives, namely indene-C60-propionic acid butyl ester and indene-C60-propionic acid hexyl ester, as the interlayers in narrow-bandgap perovskite solar cells as well as tandem solar cells. Their effects on the performance and non-radiative recombination in the devices are systematically studied.

Abstract

Interfacial engineering is the key to high-performance perovskite solar cells (PSCs). While a wide range of fullerene interlayers are investigated for Pb-based counterparts with a bandgap of >1.5 eV, the role of fullerene interlayers is barely investigated in Sn-Pb mixed narrow-bandgap (NBG) PSCs. In this work, two novel solution-processed fullerene derivatives are investigated, namely indene-C60-propionic acid butyl ester and indene-C60-propionic acid hexyl ester (IPH), as the interlayers in NBG PSCs. It is found that the devices with IPH-interlayer show the highest performance with a remarkable short-circuit current density of 30.7 mA cm⁻² and a low deficit in open-circuit voltage. The reduction in voltage deficit down to 0.43 V is attributed to reduced non-radiative recombination that the authors attribute to two aspects: 1) a higher conduction band offset of ≈0.2 eV (>0 eV) that hampers charge-carrier-back-transfer recombination; 2) a decrease in trap density at the perovskite/interlayer/C₆₀ interfaces that results in reduced trap-assisted recombination. In addition, incorporating the IPH interlayer enhances charge extraction within the devices that results in considerable enhancement in short-circuit current density. Using a NBG device with an IPH interlayer, a respectable power conversion efficiency of 24.8% is demonstrated in a four-terminal all-perovskite tandem solar cell.

Acetic acid (HAc) is first introduced to reduce the supersaturated concentration of the precursor solution to form pre-nucleation clusters, thus inducing rapid nucleation. In particular, the introduction of HAc can inhibit the oxidation of Sn²⁺ and reduce the loss of I^-. HAc-assisted device deliver a champion efficiency of 12.26%, maintaining ≈90% of initial efficiency after storage in nitrogen over 3000 h.

Abstract

Tin-based halide perovskites attract incremental attention due to the favorable optoelectronic properties and ideal bandgaps. However, the poor crystalline quality is still the biggest challenge for further progress in tin-based perovskite solar cells (PVSCs) due to the unfavorable defects and uncontrollable crystallization kinetics. Here, acetic acid (HAc) is first introduced to reduce the supersaturated concentration of the precursor solution to preferentially form pre-nucleation clusters, thus inducing rapid nucleation for effective regulation of crystallization kinetics. In particular, the hydrogen ion and acetate ion contained in HAc can effectively inhibit the oxidation of Sn²⁺, and the hydrogen bonding interaction between HAc and iodide ion (I^-) greatly reduces the loss of I^-, which guarantees the I^-/Sn²⁺ stoichiometric ratio of the corresponding perovskite film close to theoretical value, thus effectively reducing the defect density and maintaining the perfect crystal lattice. Consequently, the HAc-assisted tin-based PVSCs achieve a champion power conversion efficiency of 12.26% with superior open-circuit voltage up to 0.75 V. Moreover, the unencapsulated device maintains nearly 90% of the initial PCE even after 3000 h storage in nitrogen atmosphere. This demonstrated strategy enables to prepare high-quality tin-based perovskite film with lower defect density and lattice distortion.

Highly efficient hole transport layer-free low bandgap mixed Pb–Sn perovskite solar cells are realized using a binary additive system composed of CuSCN and GlyHCl. The improved charge transport and suppressed nonradiative recombination across the hole extractive interface have a marked impact on device performance, achieving the highest efficiency reported to date of 20.1%.

Abstract

The development of high-performance hole transport layer (HTL)-free perovskite solar cells (PSCs) with a simplified device structure has been a major goal in the commercialization of PSCs due to the economic advantage of low manufacturing cost. Unfortunately, low bandgap (E _g) mixed Pb–Sn perovskites, which have promising utility for constructing efficient all-perovskite tandem solar cells, have rarely been explored in simplified HTL-free device configurations. In this study, efficient band bending and defect engineering at the interface between perovskite and indium tin oxide (ITO) are realized via a binary additive system using copper thiocyanate (CuSCN) and glycine hydrochloride (GlyHCl). Using mixed Pb–Sn perovskites decorated with crystalline p-type CuSCN, the energy level alignment at the hole extractive interface is modulated in favor of hole extraction, simultaneously increasing hole mobility. Suppressed nonradiative carrier recombination in the perovskite bulk, or across the charge extractive interface, is further achieved by GlyHCl without disturbing the efficient hole transfer characteristics. Notably, a more optimized band alignment is achieved at the hole extractive interface with the addition of GlyHCl. The HTL-free mixed Pb–Sn PSC shows an efficiency up to 20.1% under forward bias with negligible hysteresis, comparable to state-of-the-art high-performance full-structured mixed Pb–Sn PSCs.

Biguanide hydrochloride (BGCl) is used at the tin oxide/perovskite interface for simultaneous interfacial modification and crystallization control. Assisted by Lewis coordination, electrostatic coupling and hydrogen bond anchoring between BGCl and its neighbors, better energetic alignment, reduced interfacial defects, and homogeneous perovskite crystallites are achieved, yielding an impressive power conversion efficiency of 24.4% and long-term device stability.

Abstract

Interfacial modification, which serves multiple roles, is vital for the fabrication of efficient and stable perovskite solar cells. Here, a multifunctional interfacial material, biguanide hydrochloride (BGCl), is introduced between tin oxide (SnO₂) and perovskite to enhance electron extraction, as well as the crystal growth of the perovskite. The BGCl can chemically link to the SnO₂ through Lewis coordination/electrostatic coupling and help to anchor the PbI₂. Better energetic alignment, reduced interfacial defects, and homogeneous perovskite crystallites are achieved, yielding an impressive certified power conversion efficiency (PCE) of 24.4%, with an open-circuit voltage of 1.19 V and a drastically improved fill factor of 82.4%. More importantly, the unencapsulated device maintains 95% of its initial PCE after aging for over 500 h at 20 °C and 30% relative humidity in ambient conditions. These results suggest that the incorporation of BGCl is a promising strategy to modify the interface and control the crystallization of the perovskite, toward the attainment of highly efficient and stable perovskite solar cells as well as other perovskite-based electronics.

This review presents state-of-the-art developments in 2D/3D heterostructure perovskite solar cells (PSCs) using surface passivation. The basic crystal structure, surface passivation strategy/process, optoelectronic properties, enhanced stability, and outstanding performance based on 2D/3D PSCs are systematically discussed. In addition, some emerging challenges and critical thoughts for 2D/3D PSCs are proposed to provide insights into follow-up studies.

Abstract

3D perovskite solar cells (PSCs) have shown great promise for use in next-generation photovoltaic devices. However, some challenges need to be addressed before their commercial production, such as enormous defects formed on the surface, which result in severe SRH recombination, and inadequate material interplay between the composition, leading to thermal-, moisture-, and light-induced degradation. 2D perovskites, in which the organic layer functions as a protective barrier to block the erosion of moisture or ions, have recently emerged and attracted increasing attention because they exhibit significant robustness. Inspired by this, surface passivation by employing 2D perovskites deposited on the top of 3D counterparts has triggered a new wave of research to simultaneously achieve higher efficiency and stability. Herein, we exploited a vast amount of literature to comprehensively summarize the recent progress on 2D/3D heterostructure PSCs using surface passivation. The review begins with an introduction of the crystal structure, followed by the advantages of the combination of 2D and 3D perovskites. Then, the surface passivation strategies, optoelectronic properties, enhanced stability, and photovoltaic performance of 2D/3D PSCs are systematically discussed. Finally, the perspectives of passivation techniques using 2D perovskites to offer insight into further improved photovoltaic performance in the future are proposed.

A modified additive-containing antisolvent strategy is proposed to form a poly(3-hexylthiophene) (P3HT)/perovskite bulk heterojunction for self-powered photodetectors, in which P3HT exists on the surface of the perovskite and the grain boundary. The introduction of P3HT not only passivates the interfacial defects, but also realizes a favorable band energy alignment at the interface to inhibit charge recombination, leading to enhanced performance and stability.

Abstract

Interfacial passivation and energy level alignment regulation at perovskite and charge transport layer interface are urgently desirable for constructing efficient and stable self-powered perovskite photodetectors. Herein, a modified additive-containing antisolvent strategy that not only facilitates high quality perovskite film formation but also modulates energy level alignment at interface is developed to improve the photoresponse and stability of perovskite photodetectors. Specifically, poly(3-hexylthiophene) (P3HT) is introduced as functional additive into the antisolvent chlorobenzene. P3HT molecules penetrate along perovskite grain boundaries to fill the pinholes and passivate Pb²⁺ defects. Furthermore, the valence band maximum of the surface of the perovskite layer is modulated to form a favorable band energy alignment with the hole transport layer (HTL). The suppressed carrier recombination at the perovskite/HTL interface results in reduced noise current and improved photocurrent. Finally, the optimized device achieves a responsivity of 0.41 A W^-1, a detectivity of 0.61 × 10¹² Jones at 700 nm, and a linear dynamic response range of 118 dB without external bias. In addition, the unpackaged device still maintains 78% of initial performance after 720 h under ambient conditions, indicating its superior stability compared with the original device.

A hole transport layer (HTL) with bilayer film composed of Li:NiO/NiO homojunction is developed for inverted planar perovskite solar cell. The built-in electric field and effective field in the homojunction both stimulate hole transfer from NiO to Li:NiO. The additional drive forces present a significant enhancement for carrier transport at HTL/perovskite interface to achieve a device efficiency up to 19.04%.

Abstract

Perovskite solar cells (PSCs) have been recognized as fascinating optoelectronic devices with a rapid progress of the power conversion efficiency (PCE). However, serious carrier recombination at charge transport layer (CTL)/perovskite interface limits further development of PSCs. Therefore, carrier dynamics at interface should be finely regulated to achieve a satisfied performance. Herein, a hole transport layer (HTL) is developed with a bilayer film composed of Li:NiO/NiO, in which NiO directly contacts with perovskite film. The prepared HTL is a p-p⁺ homojunction as Li:NiO film has higher concentration of carrier than NiO. Energy level alignment in Li:NiO/NiO HTL reflects a hole transport improvement by both built-in electric field and interface effective field. The additional drive forces generated by the above field effects in HTL present a significant enhancement for carrier extraction and transport at HTL/perovskite interface. As a result, the inverted planar PSC with the Li:NiO/NiO HTL delivers an improved PCE up to 19.04% from 15.40% of the control one, which also shows a high fill factor of 82.83%, indicating a low level of carrier nonradiative recombination. This work provides new insights on the carrier dynamics control in CTL/perovskite interface, which is meaningful for designing excellent PSCs.

Interfacial modification is a universal way to improve the device performance of perovskite solar cells (PSCs). However, the effect of ending groups in non-fullerene acceptors (NFAs) for interfacial passivation is still under investigation. Herein, ending groups in NFAs are found to be important in interfacial modification. The findings of this work could provide insights into designing passivation materials for high efficiency PSCs.

The defects in organic–inorganic halide perovskite films are detrimental to device efficiency and the stability of perovskite solar cells (PSCs). Interfacial modification is a universal way to passivate defects and improve device performance. However, the effect of terminal groups in non-fullerene acceptors (NFAs) on interfacial passivation in PSCs is still under investigation. Here, we demonstrate that ending groups of NFAs play an important role in interfacial modification. By comparing four different non-fullerene molecules with different ending groups (ITCC, ITIC, IT-M, IT-4F) applied as passivation layer, we found that devices with ITCC showed better performance, which was attributed to the assistance of the S atom in the ending group of ITCC enhancing adsorption to the perovskite surface compared to the ITIC case, leading to a tighter contact with the perovskite layer and better charge transfer. As a result, in FA_0.85MA_0.15Pb(I_0.85Br_0.15)₃ based PSCs, we achieved a power conversion efficiency of 21.21% and an open-circuit voltage of 1.15 V. Meanwhile, the device with ITCC showed extraordinary stability, maintaining more than 90% initial efficiency after 2000 h. The findings of this work could provide deeper insights into designing novel passivation materials at molecular scale for high efficiency and stable PSCs.

Herein, we probe that oxide thin films grown by atomic layer deposition (ALD) at low temperatures are efficient electron-transporting layers for co-evaporated perovskite solar cells (PSCs). The PSCs achieved power conversion efficiencies above 19%. We show that the low-temperature processed ALD SnO₂ is very promising for flexible and large-area PSCs and mini-modules.

In this work, we explore the potentials and the characteristics of electron-transporting layers (ETL) grown by atomic layer deposition (ALD) at low temperature in co-evaporated perovskite solar cells (PSCs). The thermal-based ALD process has been investigated by tuning the main growing conditions as the number of cycles and the growth temperature. We show that un-annealed ALD-SnO₂ thin films grown at temperatures between 80 °C and 100 °C are efficient ETL in n.i.p co-evaporated MAPbI₃ PSCs which can achieve power conversion efficiencies (PCEs) consistently above 18%. Moreover, the champion PSC achieved a PCE of 19.30% at 120 °C with 150 cycles. We show that the low-temperature processed ALD SnO₂ is very promising for flexible, large-area PSCs and mini-modules. We also report the first co-evaporated PSCs employing low temperature processed ALD ZnO with PCEs approaching 18%. This work demonstrates the potential of the low-temperature ALD deposition method as a potential route to fabricate efficient PSCs at low temperatures.

Microwave irradiation allows a quick low-temperature crystallization of nickel oxide within minutes. Moreover, the doping of In and Sn metal ions diffused from the indium tin oxide layer takes place, leading to unique chemical compositions. The perovskite solar cells with the microwave-annealed nickel oxides show better photovoltaic performances.

Solution-processed nickel oxide (NiO _x ) requires high temperatures (≈300 °C) and a long time (up to 1 h) to crystallize from precursors. Herein, thin films of NiO _x are successfully crystallized at significantly low processing temperatures of ≈130 °C within a few minutes utilizing microwave irradiation. Microwave-annealed NiO _x (MWA-NiO _x ) shows high electrical conductivity and transmittance comparable with those of conventional thermally annealed NiO _x (CTA-NiO _x ). NiO _x crystallization occurs by ohmic heating mechanisms in the indium tin oxide layer, which simultaneously facilitates the diffusion of In and Sn metal cations into the NiO _x layer. Consequently, the chemical composition in the MWA-NiO _x layer shows that both Ni²⁺ and Ni^>3+ species are reduced, which is infeasible with CTA processes, where a decrease in one species necessitates an increase in another. MWA-NiO _x is incorporated as a hole transport layer in triple-cation perovskite (Cs_0.05(MA_0.17FA_0.83)_0.95Pb(I_0.83Br_0.17)₃)-based solar cells. The short-circuit current and open-circuit voltage are enhanced compared with those of CTA-NiO _x devices owing to the combined effects of enhanced conductivity, reduced Ni^>3+ composition, and better energy-level alignment. This proposed crystallization technique of using microwave irradiation could be an effective alternative to conventional processes in improving the suitability of NiO _x for optoelectronic applications.

Perovskite solar cells deliver high efficiencies, but are often made from high-cost bespoke chemicals, such as the archetypical hole-conductor, 2,2′,7,7′-tetrakis(N,N-di-p-methoxy-phenylamine)-9-9′-spirobifluorene, spiro-OMeTAD. In this work, new charge-transporting carbazole-based enamine molecules are reported.

Perovskite solar cells deliver high efficiencies, but are often made from high-cost bespoke chemicals, such as the archetypical hole-conductor, 2,2′,7,7′-tetrakis(N,N-di-p-methoxy-phenylamine)-9-9′-spirobifluorene (spiro-OMeTAD). Herein, new charge-transporting carbazole-based enamine molecules are reported. The new hole conductors do not require chemical oxidation to reach high power conversion efficiencies (PCEs) when employed in n-type-intrinsic-p-type perovskite solar cells; thus, reducing the risk of moisture degrading the perovskite layer through the hydrophilicity of oxidizing additives that are typically used with conventional hole conductors. Devices made with these new undoped carbazole-based enamines achieve comparable PCEs to those employing doped spiro-OMeTAD, and greatly enhanced stability under 85 °C thermal aging; maintaining 83% of their peak efficiency after 1000 h, compared with spiro-OMeTAD-based devices that degrade to 26% of the peak PCE within 24 h. Furthermore, the carbazole-based enamines can be synthesized without the use of organometallic catalysts and complicated purification techniques, lowering the material cost by one order of magnitude compared with spiro-OMeTAD. As a result, we calculate that the overall manufacturing costs of future photovoltaic (PV) modules are reduced, making the levelized cost of electricity competitive with silicon PV modules.

The photoluminescence peak energy of polycrystalline formamidinium tin iodide perovskites is strongly dependent on the synthetic protocol, ageing, and oxidative stress, showing a broad distribution over more than 50 nm and slow dynamic behavior. Herein, the different sources of variation are identified and analyzed by comparing solid state synthesized powder to thin films.

The power conversion efficiency of the formamidinium tin iodide (FASI) solar cells constantly increases, with the current record power conversion efficiency approaching 15%. The literature reports a broad anomaly distribution of the photoluminescence (PL) peak position. The PL anomaly is particularly relevant to photovoltaic applications since it directly links the material's bandgap and subgap defects energy, which are crucial to extracting its full photovoltaic potential. Herein, the PL of FASI polycrystalline thin film and powder is studied. It is found that a distribution of PL peak positions in line with the distribution available in the literature systematically. The distribution in PL is linked to the octahedral tilting and Sn off-centering within the perovskite lattice, influenced by the procedure used to prepare the material. Our finding paves the way toward controlling the energy distribution of tin perovskite and thus preparing highly efficient tin halide perovskite solar cells.

Development of organic solar cells with the photoactive, hole transporting, and electron transporting layers all slot-die coated in air from halogen-free solvents, achieving a device power conversion efficiency of 10%.

Abstract

Organic photovoltaics have emerged as a low-cost and sustainable technology suitable for integration into everyday life. Record power conversion efficiencies (PCE) are rising, having surpassed 18% for single-junction devices. However, most work is still carried out using laboratory-scale techniques and conditions which are not representative of what can be achieved in an industrial setting. Herein, the use of a high-performance bulk-heterojunction (BHJ) system (i.e., PM6:Y6C12) in fabricating devices with commercially available materials, with all organic layers slot-die coated (hole transport layer, electron transport layer, and photoactive layer), without thermally treating the active layer, using non-halogenated solvents, and in ambient condition is demonstrated. A conventional architecture is used, where the hole transport layer (PEDOT:PSS), the electron transport layer (PFNBr), and the photoactive layer (PM6:Y6C12), are all slot-die coated in air from water, methanol, and o-xylene, respectively. Photovoltaic devices have an average efficiency of 10.1%, which is among the highest reported for devices with three slot-die coated layers obtained in ambient conditions from halogen-free solvents.