awn

2D/3D heterojunction perovskite is formed in situ by introducing a long-chain alkyl phenylbutylammonium (PBA⁺) cation. The surface passivation leads to the reduction of the reverse saturation current of the diode by four orders of magnitude. As a result, open circuit voltage (V _oc) and fill factor (FF) are significantly improved, and the stability of the device is also greatly improved.

The instability of 3D perovskite and the low power conversion efficiency (PCE) of 2D perovskite limit the development of perovskite solar cells (PSCs). Using 2D perovskite to passivate 3D perovskite thin films by heterojunction engineering has become an effective strategy to develop stable and efficient PSCs. Therefore, it is important to find suitable 2D perovskite passivation materials. Herein, a 2D/3D heterojunction perovskite is formed in situ by introducing a long-chain alkyl phenylbutylammonium (PBA⁺) cation. The 2D perovskite has the property of n = 2, which passivates the surface defects of the 3D perovskite, resulting in enhanced photoluminescence intensity and prolonged carrier lifetime. Moreover, the 2D layer changes the interface contact and energy-level arrangement, making it a more n-type semiconductor, which facilitates the electron transfer between perovskites and electron transport. This strategy significantly improves the open circuit voltage (V _oc) and fill factor (FF) of the devices without sacrificing current, and the PCE is improved from 19.22% to 21.76%. The hydrophobic PBA⁺-based 2D layer also improves the humidity stability of the films and enhances the working stability of the device. The PCE of the champion heterojunction perovskite device remains 87% of its initial value after illumination for 1000 h. The results show that heterojunction engineering plays an important role in the preparation of efficient and stable PSCs.

Alkali-metal ions including Na⁺, K⁺ and Rb⁺ are used to manipulate Br⁻/Cl⁻ exchange in the vapor-solid reaction process. With moderate RbI in the CsBr/PbI₂ film, high-quality perovskite films with large grain size and low trap density can be obtained. The as-prepared PSCs exhibits a significant enhancement in V _oc and achieves a champion power conversion efficiency of 19.6%.

Despite tremendous progress in efficiency and stability, perovskite solar cells are still facing the challenge of scalability and reproducibility. Vapor–solid reaction methods that derived from the chemical vapor deposition have been regarded as facile approaches to prepare perovskite films with large size. However, different from the precise control of compounding ratio by weighting in the solution process, the perovskite films deposited by vapor–solid reaction methods always suffer from undesired I⁻/Br⁻ ratio, leading to poor performance of the solar device. Thus, controllable halogen exchange in the vapor–solid reaction process is significant for the further development of this technique. Herein, different alkali-metal ions (such as Na⁺, K⁺, and Rb⁺) are added into the inorganic CsBr/PbI₂ framework, and it is found that the halogen exchange in the vapor–solid reaction process can be regulated by these ions. After optimization, high-quality Rb-Cs_0.14FA_0.86Pb(Br _x I_1-x )₃ films with proper I⁻/Br⁻ ratio are successfully obtained. Perovskite solar cells based on the as-prepared perovskite films exhibit a significant enhancement on V _oc and the champion power conversion efficiency reaches 19.6% with a V _oc of 1.13 V.

The polymer acceptor PJ1 shows strong aggregation in all-polymer solar cells when processed with o-xylene solvent. Herein, another polymer acceptor PJ2 with a similar backbone to PJ1 but much weaker aggregation ability is designed to suppress the aggregation of PJ1. Eventually, a highly efficient ternary device with the best efficiency of 14.28% is obtained.

Rapid developments in material design have led to significant breakthroughs in the power conversion efficiency (PCE) of all-polymer solar cells (all-PSCs) in recent years. However, most of these devices are processed using halogenated solvents. Here, nonhalogenated solvent o-xylene (o-XY)-processed all-PSCs based on PBDB-T:PJ1 are studied. Interestingly, it is found that the efficiency of the all-PSCs can be greatly improved to 14.34% by simply increasing the spin-coating speed during device processing. Careful studies reveal that this improvement could be attributed to the stronger centrifugal force (resulting from a higher spin-coating speed), shorten the film formation time, and inhibit the excessive aggregation of PJ1. Consequently, a blend film with more reasonable domain size is formed. Based on these findings, another polymer acceptor PJ2, which bears a similar backbone to PJ1 but contains an additional thiophene spacer, is designed. PJ2 exhibits a much weaker aggregation ability and is used as a compatibilizer to improve the miscibility between the PBDB-T and PJ1. Eventually, PBDB-T:PJ1:PJ2-based ternary all-PSCs with a best PCE of 14.28% but processed under more mild conditions are obtained. These results may provide guidelines for future industrial fabrication of large-area all-PSCs.

Dual passivation strategy for high efficiency inorganic CsPbI₂Br solar cells is demonstrated. A synergetic effect from the dual passivation of the trap defects in the CsPbI₂Br film by KBr and phenethylammonium chloride (PEACl) is demonstrated, which is beneficial to the better growth of the CsPbI₂Br film with reduced trap defects, enlarged grain size, and formation of an ultrathin low-dimensional perovskite surface layer.

Inorganic metal halide perovskite solar cells have achieved incredible progress in recent years. However, the power conversion efficiency of the inorganic perovskite solar cells is still low compared with their hybrid counterparts due to the inescapable nonradiative losses from the charge recombination. Herein, a strategy is demonstrated to minimize the nonradiative recombination loss in CsPbI₂Br solar cells by establishing a synergetic passivation from the mutual effect of alkali- and alkylammonium-salt. Accordingly, a sequential passivation process employing KBr and phenethylammonium chloride overcomes their limited passivation effect in one single step. This dual passivation is beneficial to an improved CsPbI₂Br film with reduced trap defects, enlarged grain size, as well as to form an ultrathin low-dimensional perovskite surface layer. As a result, a very high power conversion efficiency of 16.9% is obtained for inorganic CsPbI₂Br solar cells. The proposed dual passivation scheme provides a feasible route not only for the design of high-efficiency perovskite solar cells but also for other perovskite-related optoelectronic devices.

It is discovered that the morphology of the as-prepared perovskite film is greatly affected by the surrounding temperature during spin-coating. The optimal surrounding temperature of 29 °C is observed to dramatically enlarge the perovskite crystal size and increase the power conversion efficiency of perovskite solar cell to 20.91%, which is the highest reported value among inverted MAPbI₃ solar cells.

Controlling the crystallization of perovskite film is critical for high-performance perovskite solar cells (PVSCs), and temperature is the key factor dominating the nucleation and crystal growth. Herein, it is demonstrated that the inconspicuous ambient temperature plays an important role in reaching high-quality perovskite film and high-performance PVSCs. It is observed that the ambient temperature greatly affects the composition of as-prepared perovskite film, which dramatically influences the perovskite film morphology during the subsequent annealing process. Remarkably, the device prepared at the optimal ambient temperature of 29 °C exhibits the best power conversion efficiency of 20.91% with little hysteresis. This represents one of the best results for inverted PVSCs based on pristine MAPbI₃ system. In addition, the PVSC prepared at 29 °C shows good stability with 80% of its initial efficiency after 30d in air with a humidity of 45%. Overall, the importance of ambient temperature for crystallization of the perovskite film is emphasized, and this work should have implications for controlling the morphology for high-performance PVSCs.

A systematic comparison of highly efficient perovskite solar cells made from one-step and two-step processes has been reported. Through various analyses, perovskite film properties including nucleation, optical property, morphological property, location of inorganic residue, and excess of organic salts are unveiled. Overall, perovskite made by one-step is less uniform horizontally, while perovskite made by two-step is less uniform vertically.

One-step and two-step methods are regarded as the main solution processes for preparing organic metal halide perovskite (PVSK) films. Both of them are also reported to produce high-quality PVSK films and high-performance devices. Herein, two highly efficient perovskite solar cells (PSCs) made by one-step (19.91%) and two-step (20.63%) methods are analyzed in detail. Particularly, the nucleation mechanism and structural characteristics of the PVSK films made from different methods are systematically discussed. Characterizations from field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), Kelvin probe force microscopy (KPFM), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) show that the ion distribution in the PVSK film made by the one-step method is less uniform horizontally, while the PVSK film made by the two-step method is less uniform vertically. Both films contain a considerable amount of unreacted species, including PbI₂, cations, and halides, which are relics from their parental fabricating process. Despite these significant differences, both films are capable to deliver nearly 20% conversion efficiency. This study depicts a clear picture of the PVSK film properties made by one-step and two-step methods and provides plentiful information for further improvement in the future.

The intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) response of perovskite solar cells is accurately resolved, demonstrating that features commonly observed at high frequency in literature reports are due to artefacts caused by limitations of standard instruments. The time dependence of the IMPS/IMVS response shows clear links to effects of ion migration on the electric field and interfacial recombination rates within devices.

The complete interpretation of small perturbation frequency-domain measurements on perovskite solar cells has proven to be challenging. This is particularly true in the case of intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) measurements in which the high frequency response is obscured by instrument limitations. Herein, a new experimental methodology capable of accurately resolving the high frequency response—often observable in the second and third quadrants of the complex plane—of a range of perovskite devices is demonstrated. By combining single-frequency IMPS/IMVS measurements, it is able to construct the time dependence of the IMPS/IMVS response of these devices during their initial response to illumination. This reveals significant negative photocurrent/photovoltage signals at high frequency while devices reach steady state, which is in keeping with observations made from comparable time-domain transient measurements. These techniques allow the underlying interfacial recombination and ion migration processes to be assessed, which are not always evident using steady-state measurements. The ability to study and mitigate these processes is vital in optimizing the real-world operation of devices.

The structure–properties relationships of hole transport materials (HTMs) with fused and unfused core units are investigated. The HTM with a fused core exhibits a high hole mobility and an efficient charge extraction capability, leading to a remarkable efficiency of 19.63% when it is used as an HTM without any dopant, much higher than unfused HTM-based devices (10.03%).

Replacing the dominating and dopant-needing 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamino)-9,9′-spiro-bifluorene (spiro-OMeTAD) with dopant-free organic hole transport materials (HTMs) in n-i-p structured perovskite solar cells (PSCs) is a big challenge. Herein, a class of conjugated organic semiconductor materials, namely, ZT-H1 and ZT-H2, with unfused and fused core units, respectively, are successfully designed and synthesized for dopant-free HTMs. It is found that the HTM ZT-H1 exhibits a hole mobility of 7.08 × 10⁻⁵ cm² V⁻¹ s⁻¹, which is improved to 5.16 × 10⁻⁴ cm² V⁻¹ s⁻¹ for HTM ZT-H2 due to the enlarged molecular planarity of ZT-H2, leading to efficient intermolecular π–π interaction. Further investigation indicates that ZT-H2 is more fit to facilitating hole extraction, restraining charge recombination, and guaranteeing long-term stability of the devices. Consequently, a planar n-i-p structured device using ZT-H2 as HTM without any dopants exhibits a remarkable efficiency of 19.63%, which is much higher than that of ZT-H1-based devices (10.64%). Importantly, ZT-H2-based devices are much more stable than the control devices using ZT-H1 or spiro-OMeTAD as the HTM. The findings reveal that the fused central core unit with extended π-conjugation is an efficient strategy for rationally designing dopant-free HTMs toward stable and efficient PSCs.

The progress on p-type tunnel oxide-passivated contact (TOPCon) solar cells with boron-doped passivating rear contacts is highlighted herein. The impact of the polysilicon layer thickness on contact recombination and contact resistivity for several screen-printed metallization pastes is reported upon. Hydrogenation of the TOPCon interface is improved by providing a fresh SiN _x :H layer. Fabricated solar cells show conversion efficiencies of 21.2%.

Herein, an update on the work on high-efficiency p-type solar cells with p-type-passivating rear contacts formed by low-pressure chemical vapor deposition and screen-printed contacts is given. It is shown that thin polysilicon layers enable a high level of surface passivation but do show increased contact resistivity and especially contact recombination. Commercially available pastes and dependence of contact resistivity and contact recombination on polylayer thickness and firing set temperature are investigated. For 240 nm-thick poly-Si layers, the values down to 4 mΩ cm² and 60 fA cm^{− 2} are observed. For the presented process sequence, improved hydrogenation as one possibility to increase the passivation quality of the passivating contact structure is identified. Implementing all findings into a final solar cell, a maximum total area conversion efficiency of 21.2% is reported.

Liquid-exfoliated 2D transition-metal dichalcogenides (MoS₂, WS₂, and WSe₂) are introduced as growth templates for spin-coated FASnI₃ perovskite films, leading to van der Waals epitaxial growth of perovskite grains with a growth orientation along (100). The good energy alignment in the NiO _x /WSe₂/FASnI₃ structure facilitates hole extraction and suppresses interfacial charge recombination, leading to the best PCE of 10.47% for the PSC.

Abstract

Tin (Sn)-based perovskites with favorable optoelectronic properties and ideal bandgaps have emerged as promising alternatives to toxic lead (Pb)-based perovskites for photovoltaic applications. However, it is challenging to obtain high-quality Sn-based perovskite films by solution process. Here, liquid-exfoliated 2D transition-metal dichalcogenides (i.e., MoS₂, WS₂, and WSe₂) with smooth and defect-free surfaces are applied as growth templates for spin-coated FASnI₃ perovskite films, leading to van der Waals epitaxial growth of perovskite grains with a growth orientation along (100). The authors find that WSe₂ has better energy alignment with FASnI₃ than MoS₂ and WS₂ and results in a cascade band structure in resultant perovskite solar cells (PSCs), which can facilitate hole extraction and suppress interfacial charge recombination in the devices. The WSe₂-modified PSCs show a power conversion efficiency up to 10.47%, which is among the highest efficiency of FASnI₃-based PSCs. The appealing solution phase epitaxial growth of FASnI₃ perovskite on 2D WSe₂ flakes is expected to find broad applications in optoelectronic devices.

Semitransparent solar cells can bring us a green, smart, and comfortable life powered by sun and compatible to our living buildings. In article number 2001604, Hui Pan, Zhubing He, and co‐workers develop high performance semitransparent perovskite solar cells in multidisciplinary applications, such as tandem solar cells, building integrated photovoltaics, smart window and etc.

This article reports the interfacial modification of mesoporous TiO₂ electron transport layer with ultrathin Nb₂O₅ using atomic layer deposition technique. This interlayer facilitates charge transfer and reduces charge carrier recombination pathways at interfaces. In addition, the performance and stability after prolong exposure to high humidity, temperature, and UV irradiation of the Nb₂O₅-modified devices are improved.

Abstract

There has been tremendous advancement in the field of perovskite photovoltaics by means of interfacial engineering, compositional engineering and optimization of charge collection efficiency. The large bandgap oxides deposited using atomic layer deposition (ALD) technique have proven to be successfully passivating the interfacial defects owing to the advantages offered by this technique. Here, the effect of surface modification of mesoporous TiO₂ (ms-TiO₂) layer with a transition metal oxide named niobium pentoxide (Nb₂O₅) deposited by ALD technique on the performance and stability of perovskite solar cells (PSCs) is investigated. The results reveal that functionalization with ultrathin Nb₂O₅ layer improve the optoelectronic properties and morphology of the deposited perovskite films. Moreover, the charge transfer is improved and hence the interfacial recombination is reduced. This results in improved power conversion efficiency (PCE) from 19.11% to 21.04% and open-circuit voltage (V _OC) from 1.118 to 1.147 V for the modified champion device. Additionally, the device shows negligible hysteresis with enhanced shelf life thermal and UV stabilities.

The titanium diisopropoxide bis(acetylacetonate) molecules are incorporated into tin oxide (SnO₂) nanoparticle solution, in which the TiO₄ ^4– core, functional CO, and long alkene groups are used to tune the energy level, morphology, conductivity, and surface intimacy of the SnO₂ layer. As a result, the efficiency of perovskite solar cells is boosted from 18% to above 20% with significantly reduced hysteresis.

Abstract

Solution-processed tin oxide (SnO₂) is ubiquitously used as the electron transport layer (ETL) in perovskite solar cells, while the main concerns related to the application of SnO₂ nanoparticles are the self-aggregation potential and infeasible energy level adjustment, leading to inhomogeneous thin films and mismatched energy alignment with perovskite. Herein, a novel route is developed by adding a functional titanium diisopropoxide bis(acetylacetonate) (TiAcAc) molecule, comprising TiO₄ ^4– core, functional CO, and long alkene groups, into the SnO₂ nanoparticle solution, to optimize the electronic transfer property of SnO₂ for efficient perovskite solar cells. It is found that the TiO₄ ^4– can be used to tune the electronic property of the SnO₂ layer, and the long alkenes can act as a stabilizer to avoid the nanoparticle aggregation and electronic glue among the SnO₂ nanoparticles in the eventual nanoparticulate thin film, enhancing its homogeneity and conductivity. Furthermore, the residual CO groups on the ETL surface can strongly associate with the Pb²⁺ and improve the interface intimacy between the ETL and perovskite. As a result, the efficiency of perovskite solar cells can be boosted from 18% to above 20% with significantly reduced hysteresis by employing SnO₂-TiAcAc as electron transport layer, indicating a great potential for efficient perovskite solar cells.

A thermally stable superhydrophilic glass substrate is prepared by a facile chemical etching process using a mild base. This is an ideal template not only for printing high-quality single-crystal organic semiconductor thin films, but also for transferring them onto a destination substrate. The fabricated thin-film transistors exhibit an outstanding electron mobility of 2.2 cm² V⁻¹ s⁻¹.

Abstract

Thin-film devices are typically fabricated through a bottom-up approach, wherein the constituents are deposited sequentially from the bottom to top layer. This method requires the precise management of the heterointerfaces, which leads to complicated integration issues particularly in solution-processed organic thin-film transistors (OTFTs). This limitation arises because a surface suitable for the printing of semiconductors is not necessarily suitable for maximizing the electronic properties of OTFTs. To overcome this, a transfer technique of organic semiconductor (OSC) thin films has been studied. This enables facile transfer of the OSC thin film from a hydrophilic template to any given substrate; thus, the printing substrate and destination substrate can be optimized individually. Here, a nano-ground glass (NGG) is developed whose surface is chemically etched using a mild base. The NGG functions as a thermally stable, superhydrophilic template for printing high-quality single-crystal OSC thin films. To evaluate the practical applicability of the NGG, an n-type OSC, which requires a relatively high temperature of around 150 °C during crystal growth, is fabricated. The fabricated OTFTs exhibit an outstanding electron mobility of 2.2 cm² V⁻¹ s⁻¹. The NGG proposed in this study can be utilized for the fabrication of a wide variety of printable materials.

Publication date: 21 April 2021

Source: Joule, Volume 5, Issue 4

Author(s): Di Yan, Andres Cuevas, Jesús Ibarra Michel, Chun Zhang, Yimao Wan, Xinyu Zhang, James Bullock

A low-dimensional perovskite layer is constructed between the perovskite absorber and carbon electrode in printable triple-mesoscopic perovskite solar cells by posttreatment. By forming graded type-II band alignment, the device performance is significantly enhanced, delivering a power conversion efficiency of 17.47% with an open-circuit voltage of 1.02 V.

Abstract

Printable hole-conductor-free perovskite solar cells (PSCs) have attracted intensive research attention due to their high stability and simple manufacturing process. However, the cells have suffered severe potential loss in the absence of the hole transporting layer. The dimensionality of the perovskite absorber in the mesoporous carbon electrodes by conducting post-treatments is reduced. The low-dimensional perovskites possess wide-bandgaps and form type-II band alignment, favoring directional charge transportation and thus enhancing the device performance. For the cells using MAPbI₃ (MA = methylammonium) as the light absorber, the open-circuit voltage (V _OC) is significantly enhanced from 0.92 to 0.98 V after posttreatment, delivering an overall efficiency of 16.24%. For the cells based on FAPbI₃ (FA = formamadinium), a high efficiency of 17.47% is achieved with V _OC of 1.02 V, which are both the highest reported values for printable hole-conductor-free PSCs. This strategy provides a facile method for tuning the energy level alignment for mesoscopic perovskite-based optoelectronics.

A patterned blade coating strategy is investigated to print non-fullerene based devices, with a PCE of 15.93%. The designed patterned blade enhances fluid flow to optimize morphology evolution kinetics for achieving an optimized morphology and device reproducibility. In addition, the versatility in large-area devices and other systems is also shown.

Abstract

Morphology evolution kinetics at multi-scale regime is a challenging problem which is critical for industrial fabrication of high-performance organic solar cells (OSCs). An innovative strategy utilizing a patterned blade to print non-fullerene (NF) based devices in ambient conditions is demonstrated. A specially designed patterned blade with micro-cylinder arrays exhibit a reasonable control over the fluid flow at high extensional and shear strain rate to enhance lateral mass transport during blade-coating. Comparison of patterned and normal blade in printing polymer:NF blend film at different speeds reveals interesting avenues to optimize the blend films morphology. Patterned blade printed PM6:Y6 films yield a PCE of 15.93% as compared to 14.55% from a normal blade. Through in situ and ex situ morphology characterization techniques, the use of patterned blades induce conformational changes in PM6 chains, enabling Y6 to crystallize faster and more efficiently. Such improved blend morphology enables favorable charge transfer and transport to realize superior device performance. A lower stick-slip effect at the macro-scale with the patterned blade results in a smoother film promoting device reproducibility. Applications in efficient large-scale devices, confirming the choice of patterned blade design are reported. The efforts collaborating device engineering, morphology evolution kinetics would enable reproducibility and eased commercialization of OSCs at large scale.

The polymeric melt encapsulation method is a good method for the preparation of all-inorganic perovskite quantum dots (PQDs) PQDs@polymer. It can be used to prepare a CsPbBr₃ QDs/polymethyl methacrylate (PMMA) composite with excellent performance: ≈82.7% photoluminescent quantum yield, ≈18.6 nm full width at a half-maximum, ≈32.5 nm lifetime. It has the advantages of being a one-step, ligand free, solvent free, low synthetic temperature approach and is easy to industrialize, indicating broad application prospects.

Abstract

All-inorganic CsPbBr₃ perovskite quantum dots (PQDs) exhibit excellent photoelectric properties and application prospects in the field of light-emitting diodes (LEDs) and display devices. However, these possess poor long-term stability to UV irradiation, water, heat, and oxygen. Using polymethyl methacrylate (PMMA) as the matrix along with CH₃(CH₂)₁₆COOCs, [CH₃(CH₂)₁₆COO]₂Pb, and KBr as the perovskite sources, CsPbBr₃ PQDs/PMMA composites are for the first time prepared via an in situ polymeric melt encapsulation method. Special attention is paid to the effects of synthesis conditions on the photoluminescent quantum yield (PLQY) of the composites. The optimized CsPbBr₃ PQDs/PMMA composite reveals excellent performance with ≈82.7% PLQY and ≈18.6 nm full width at a half-maximum (FWHM). In particular, after 90 h of UV irradiation or 35 days of heating at 60 °C, the luminous intensity remains almost unchanged. In addition, after soaking in water for 15 days, it retains up to ≈53% of the initial luminous intensity, meaning that the composite possesses long-term stability to UV irradiation, heat, and water. The as-prepared white LED (WLED) based on the composite evidences the wide color gamut (126.5% National Television System Committee (NTSC)) and a luminous efficiency of 32 lm W⁻¹. This work offers a novel, easily industrialized one-step, and solvent free route for low-temperature synthesis of all-inorganic PQDs with broad application prospects.

Two anthracene diimide polymers are synthesized and used as the acceptor in all-polymer solar cells (all-PSCs) for the first time, offering the best device efficiency of ≈7%. Moreover, general guidelines for screening donor/acceptor polymer combinations for all-PSCs are proposed by investigating their crystallinity and orientation behaviors in blend films.

Abstract

Electron-carrying polymers are highly desired for various optoelectronic applications but are still scarce. Herein, two anthracene diimide (ADI) polymers with thiophene and bithiophene as comonomer, respectively, are reported as electron acceptor materials in all-polymer solar cells (all-PSCs) for the first time. Effects of crystallinity and orientation of two polymer films as well as their blends with different donor polymers on photovoltaic properties are elaborately investigated by grazing-incidence X-ray diffraction and photo-induced force microscopy. It is found that molecular crystallinity and orientation determine the blend film morphology, and the similar high crystallinity and the same face-on orientation of donor and acceptor polymers are favorable for obtaining excellent photovoltaic performances. With this principle, a suitable donor polymer is singled out to match with the ADI acceptor polymer, offering an impressive efficiency of ≈7% for all-PSCs. This work demonstrates that ADI polymers are promising as acceptor materials and provides guidelines for screening donor and acceptor polymer combinations for all-PSCs.

Two novel triarylamine-based donor-acceptor copolymers featuring an imide-functionalized backbone are developed. Benefiting from the good energy level alignment, appropriate film morphology, and most importantly, improved hole mobility, the pristine PTTI-TPA based inverted perovskite solar cells achieve a high power conversion efficiency of up to 21% with negligible hysteresis and substantial stability.

Abstract

Dopant-free hole-transporting layers (HTLs) are highly desired for realizing efficient and stable perovskite solar cells (PVSCs), but only very few of them can enable power conversion efficiencies (PCEs) over 20%. Herein, two imide-functionalized triarylamine-based donor-acceptor (D-A) type copolymers, PBTI-TPA and PTTI-TPA, are developed and applied as dopant-free HTLs in inverted PVSCs. The combination of a classic redox-active triphenylamine donor unit and an electron-withdrawing oligothiophene imide co-unit with rigid and planar backbone furnishes the two polymers with quasi-planar backbone, suitable frontier molecular orbital (FMO) energy levels, favorable thermal stability, appropriate film morphology, and passivation effect. More importantly, the greatly improved hole mobility renders them as promising HTLs for PVSCs. As a result, the undoped PTTI-TPA-based inverted PVSCs deliver a remarkable PCE up to 21% as well as negligible hysteresis and substantial long-term stability, outperforming the devices based on PBTI-TPA and PTAA. The performance also represents one of the highest PCEs reported to date for PVSCs based on dopant-free polymeric HTLs. The results highlight the great potentials of oligothiophene imides for constructing donor-acceptor polymeric HTLs for enabling high-performance dopant-free PVSCs.

A room temperature synthesis method of ultrathin CsPbX₃ (X = Cl,Br,I) perovskite nanowires is developed. Based on the controllable equilibrium of nanocrystals in solution, reversible transform between CsPbBr₃ nanowires and nanorods are revealed. The assembled perovskite nanowires/nanorods films show outstanding polarized optoelectronic properties. Polarized light detectors are fabricated to demonstrate their application potentials.

Abstract

CsPbX₃ (X = Cl, Br, I) perovskite nanowires and nanorods are important 1D and quasi 1D semiconductor nanomaterials. They have shown significant prospect in optic and optoelectronic applications, especially for their adaptability to flexible devices, good carrier transport performance, polarized absorption, and emission properties. Due to the high dependence of the property to the morphology, it is crucial to develop synthesis methods with continuous diameter and length tunability of the 1D/quasi 1D perovskites. In this report, a feasibly room temperature synthesis method was developed for ultrathin CsPbX₃(X = Cl, Br, I) perovskite nanowires. By aging the CsPbBr₃ nanowires (≈2*500 nm) under ambient condition with proper concentration and time, the nanowires are transformed to nanorods with controllable diameter and length. Reversibly, the nanorods can be transformed back to nanowires. Equilibrium mechanism is adopted to understand the morphology evolution, and hopefully could be generally applied to many other nano materials. The polarized optoelectronic properties of the nanowires and nanorods are interpreted by a model based on the two-channel anisotropies measurement. Polarized light detectors constructed by oriented assembled nanowires are fabricated to demonstrate their application potentials.