Interface Modification Engineering
In article number 19000162, Qiuhong Cui, Yanbing Hou, and co‐workers construct perovskite solar cells with discrete SnO2 nanoparticle‐modified layers by spin coating the SnO2 dispersions on PEDOT:PSS. The discrete SnO2 nanoparticle film lets holes pass and block electrons to diffuse toward PEDOT:PSS, which enhances the extraction efficiency, leading to an increase in power conversion efficiency.
Chlorine‐Substituted Graphdiyne
In article number 1900241, Tonggang Jiu and co‐workers introduce chlorine‐substituted graphdiyne into MAPbI3‐based perovskite solar cells to produce a peak efficiency of 20.34% with suppressed J‐V hysteresis, which results from the interaction of derivated graphdiyne and PCBM, to be exact, four types of non‐covalent bonds. These findings suggest that derivated graphdiyne could have potential applications in solar cells and other photoelectric devices.
Zero‐Dimensional Perovskites
In article number 201900127, Xiaosheng Tang, Juan Du, Yuxin Leng, and co‐workers study the photophysical properties of zero‐dimensional Cs4PbBr6 by using femtosecond transient absorption measurements; the existence of polarons provides evidence of the inherent green emission from Cs4PbBr6. Furthermore, the excellent stable lasing performance at room temperature from Cs4PbBr6 perovskite microdisks is successfully achieved.
Organic solar cells are a promising low‐carbon technology for electricity generation. Recently, such cells have reached the milestone of 17% power conversion efficiency. Herein, the key players behind this recent surge in efficiency are discussed. Novel organic photovoltaic materials and device architectures are critically reviewed. Non‐fullerene donors and acceptors dramatically increase device efficiency.
Organic solar cells (OSCs) are one of the most promising low‐carbon technologies for the generation of electricity. It is blessed with a relatively lower installation time and cost, light weight, semitransparent nature, and suitability for roll‐to‐roll printing process. In the past, critics of OSCs were concerned about its limited efficiency compared with other contemporary photovoltaic (PV) technologies. However, in the past few years, researchers in this field have made sufficient progress in terms of high performance, and OSC efficiency has witnessed significant growth. Today, a large number of OSCs are demonstrating >10% efficiency, recently reaching the milestone of 17%. The boost in efficiency is crucial for the successful commercialization of OSC. Herein, the recent advancements in OSC are highlighted to analyze the key players working behind the surge in its efficiency. The contributions of novel organic photovoltaics materials and their morphology as well as novel device architectures are discussed. Finally, the major challenges facing the upscaling and commercialization of OSCs are addressed.
Herein, a facile method is provided to fabricate the CsPbIBr2 inorganic perovskite solar cells under low temperatures. The ZnO electron transport layer modification and band‐alignment engineering contribute to the outstanding power conversion efficiency of 10.16%, representing the highest efficiency for CsPbIBr2 when the fabrication temperature is lower than 160 °C.
Recently, the thermally stable and facilely fabricated inorganic CsPbIBr2 perovskite solar cells (PSCs) have attracted tremendous attention where the electron transport layer (ETL) is vital. However, the typical sintering temperature for the widely used electron transport material, that is, TiO2, is more than 400 °C, elevating the cost and hindering the application. Due to high electron mobility and low fabrication temperature, ZnO becomes a desirable alternative for TiO2, as the ETL in CsPbIBr2 PSCs, albeit with low open‐circuit voltage (V oc). Herein, this work introduces a trace of NH4Cl to the sol–gel‐derived ZnO precursor to decrease the work function of the ZnO film, tune the surface morphology of the perovskite film, and thus suppress the density of trap states in the CsPbIBr2 films. Consequently, full‐coverage and pure‐phase CsPbIBr2 films consisting of micron‐size and high‐crystallinity grains are obtained. More importantly, for the optimal NH4Cl‐modified ZnO, a shining improvement in V oc from 1.08 to 1.27 V boosts the champion CsPbIBr2 PSCs to obtain a power conversion efficiency of 10.16%, which is the highest value reported among pure‐CsPbIBr2 PSCs under a low fabrication temperature of 160 °C. In addition, the NH4Cl‐modified ZnO ETL reduces the severe hysteresis and increases the device stability significantly.
Propyl ammonium (C3A) is introduced into phenethylammonium (PEA)‐based 2D perovskites with <n> = 3. It is found that tuning the CH···π interaction between organic cations can remove undesirable n = 1 phase, lower the density of trap states, and achieve larger crystalline grains to improve the perovskite solar cell efficiency to ≈10%. C3A with other aromatic cations shows similar improvement.
Phenethylammonium (PEA)‐based 2D perovskite is an interesting example of 2D perovskites, serving as the gateway for further introduction of functional conjugated organic cations into 2D perovskites for a variety of applications, for example, photovoltaics. However, the efficiency of photovoltaic devices based on PEA 2D perovskites only achieved ≈7% for <n> = 3, which was significantly lower than that achieved for other cation‐based 2D perovskites. Here, by introducing propyl ammonium (C3A) into the PEA‐based 2D perovskites, the device efficiency is improved to ≈10% for 1:1 C3A:PEA‐based 2D perovskites (<n> = 3). Further investigation reveals that tuning the CH···π interaction (between C3A and PEA or between two PEA molecules) can have multiple beneficial impacts on such modified 2D perovskites, including a) removal of undesirable n = 1 phase, b) lowering the density of trap states, and c) achieving larger crystalline grains. Additionally, after substitution with 50% C3A, other aromatic ammonium cation‐based 2D perovskites (<n> = 3) also show similar efficiency enhancement in their photovoltaic devices, thus exhibiting the general applicability of this method. The results of this study highlight that the strategic tuning of non‐covalent interactions (such as CH···π interaction) is a viable and important method to further develop 2D perovskites for photovoltaics.
![Solar RRL Regioisomer‐Free Chlorinated Thiophene‐Based Ending Group for Thieno[3,2‐b]thiophene Central Unit‐Based Acceptor Enabling Highly Efficient Nonfullerene Polymer Solar Cells with High Voc Simultaneously](https://onlinelibrary.wiley.com/cms/asset/cccf80fd-403a-4f1d-9ac9-c4ed57da1ac0/solr201900446-blkfxd-0001-m.png)
An effective method is proposed for excellent power conversion efficiency (PCE) with high V oc in polymer solar cells (PSCs) by introducing a weak electron‐deficient thiophene‐based IC terminal group into thieno[3,2‐b]thiophene central core‐based small molecule acceptors. An excellent PCE of 13.11% with V oc of 0.88 V is obtained, which is the highest reported for A–D–A‐type nonfullerene acceptors containing the central thieno[3,2‐b]thiophene unit with sp3 hybridized carbon‐bridged cyclopentadiene fragments in binary PSCs.
A pair of pure regioisomeric acceptor–donor–acceptor (A–D–A) typed nonfullerene small molecule acceptors (NF‐SMAs) (4TTIC and 4TTIC‐Cl), containing a central thieno[3,2‐b]thiophene‐sp3 hybridized “carbon‐bridge”‐based fused ring core unit and thiophene‐based IC or chlorinated thiophene‐based IC are synthesized for polymer solar cells (PSCs). Compared with 4TTIC, 4TTIC‐Cl not only achieves a red‐shifted absorption spectra and lower energy levels but also enhancement of molecular packing and crystallinity. The 4TTIC‐Cl‐based blend films display higher and more balanced charge carrier mobilities, more favorable morphology, and more efficient exciton dissociation in comparison with the 4TTIC‐based blend film. The optimized devices based on PBDB‐ST:4TTIC‐Cl deliver an impressively high power conversion efficiency (PCE) of 13.11% and fill factor of 74%, much higher than that of the PBDB‐ST:4TTIC‐based devices. Moreover, a small energy loss of ≈0.54 eV and a decent V oc of 0.88 V are simultaneously achieved for PBDB‐ST:4TTIC‐Cl‐based devices. Noticeably, the PCE of 13.11% is the highest reported value for NF‐SMAs containing the central thieno[3,2‐b]thiophene unit with sp3 hybridized carbon‐bridged cyclopentadiene fragments in binary PSCs. This study proves that introduction of less electron‐deficient thiophene‐based IC terminal group into thieno[3,2‐b]thiophene central core‐based SMAs is a very effective method for making high V oc and excellent PCE simultaneously.
Carbon quantum dots (CQDs) are introduced as hole injection layer (HIL) in perovskite light‐emitting diodes (PeLEDs) to substitute highly acidic poly(3,4‐ethylenedioxythiophene):poly styrene sulfonate (PEDOT:PSS). The surface‐functionalized CQDs' HIL owns suitable band alignment and high hole mobility, and can significantly suppress the luminescence quenching effect at the HIL/perovskite interface, resulting in greatly enhanced external quantum yield and operational stability of PeLEDs.
For metal halide perovskite (MHP)‐based light‐emitting diodes (PeLEDs), effective radiative recombination of the injected holes and electrons within the MHP layer and minimized injection energy barriers at the interfaces between MHP emission layer and charge injection layers are prerequisites for high‐performance and stable PeLEDs. Herein, for the first time, novel p‐type carbon quantum dots (CQDs) are introduced as a hole injection layer in PeLEDs to replace acidic poly(3,4‐ethylenedioxythiophene):poly styrene sulfonate (PEDOT:PSS) layer. The CQDs demonstrate high hole transport mobility and desirable hole injection energy level. Moreover, the carboxyl, amine, and hydroxyl groups on CQDs not only offer a hydrophilic surface for high‐quality perovskite layer growth, but also passivate the perovskite surface defects to suppress the interfacial exciton quenching. Based on the multifunctional p‐type CQDs, high‐performance green CsPbBr3 PeLEDs with a low turn‐on voltage of only 2.8 V, maximum luminance of 25 770 cd m−2, and maximum external quantum efficiency (EQE) of 13.8% are achieved. The PeLEDs also show good operational stability and long‐term environmental stability. The first application of CQDs as a hole injection layer in PeLEDs breaks through the traditional cognition of carbon materials and opens up new pathways for the developments of carbon nanomaterials in optoelectronic devices.
A 0D Cs4PbI6/3D CsPbI3 heterostructure is achieved by tuning the stoichiometry of the precursors. The coexistent Cs4PbI6 not only reduces the grain size of the CsPbI3 and serves as a molecular lock to stabilize the black‐phase CsPbI3, but also passivates the defects in the grain boundaries and improves the surface coverage to improve the device performance to 16.39%.
Although organic–inorganic hybrid perovskite solar cells (PVSCs) have achieved dramatic improvement in device efficiency, their long‐term stability remains a major concern prior to commercialization. To address this issue, extensive research efforts are dedicated to exploiting all‐inorganic PVSCs by using cesium (Cs)‐based perovskite materials, such as α‐CsPbI3. However, the black‐phase CsPbI3 (cubic α‐CsPbI3 and orthorhombic γ‐CsPbI3 phases) is not stable at room temperature, and it tends to convert to the nonperovskite δ‐CsPbI3 phase. Here, a simple yet effective approach is described to prepare stable black‐phase CsPbI3 by forming a heterostructure comprising 0D Cs4PbI6 and γ‐CsPbI3 through tuning the stoichiometry of the precursors between CsI and PbI. Such heterostructure is manifested to enable the realization of a stable all‐inorganic PVSC with a high power conversion efficiency of 16.39%. This work provides a new perspective for developing high‐performance and stable all‐inorganic PVSCs.
Nature Materials, Published online: 14 October 2019; doi:10.1038/s41563-019-0527-9
Author Correction: Titanium-carbide MXenes for work function and interface engineering in perovskite solar cellsPublication date: December 2019
Source: Nano Energy, Volume 66
Author(s): Jibin Zhang, Xiangfu Liu, Pengfei Jiang, Hongting Chen, Yao Wang, Jinming Ma, Rui Zhang, Fei Yang, Mingkui Wang, Jian Zhang, Guoli Tu
All inorganic perovskite CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) have been endowed great promise for optoelectronic device applications. However, further practical applications of these NCs are blocked because of their poor stability. In the present work, we propose a novel strategy to synthesize highly luminescent and stable red-emitting CsPbBrI2/PbSe heterojunction nanocrystals (h-NCs) via an epitaxial solution growth method, in which lattice-matching condition between CsPbBrI2 and PbSe was satisfied, and each CsPbBrI2 NC was partially covered by PbSe in the CsPbBrI2/PbSe heterodimers. The ultrafast transient absorption (TA) and time-resolved photoluminescence (TRPL) spectroscopy revealed that incorporation of PbSe can modify surface and hence passivate the surface trap states of the CsPbBrI2 NCs, helping to enhance the photoluminescence quantum yields (PLQY) (up to 83.4%) of these CsPbBrI2/PbSe h-NCs. First-principle calculations based on DFT confirmed that the significantly improved stability of these CsPbBrI2/PbSe h-NCs was attributed to the strong chemical bonding of selenium atoms of PbSe and lead atoms of PbX2-terminated surface from CsPbBrI2. Thin films of these CsPbBrI2/PbSe h-NCs can maintain bright red PL brightness and cubic phase even after 15-day storage under a high humidity condition. Benefiting from the performances of high stability and luminescent efficiency, these red-emitting CsPbBrI2/PbSe h-NCs have a positive implication for bright light-emitting diodes (LEDs).
CsPbBrI2/PbSe heterojunction nanocrystals (h-NCs) show higher stability and photoluminescence quantum yield (PLQY) than those of pristine CsPbBrI2 NCs. Thin films of these CsPbBrI2/PbSe h-NCs can maintain bright red PL brightness and cubic phase even after 15-day storage under a high humidity condition, while pristine CsPbBrI2 NCs will decompose and show green PL brightness within exposure to 15 days under the same conditions.
Publication date: December 2019
Source: Nano Energy, Volume 66
Author(s): Zhen Wang, Ajay K. Baranwal, Muhammad Akmal kamarudin, Putao Zhang, Gaurav Kapil, Tingli Ma, Shuzi Hayase
All-inorganic perovskites have drawn tremendous attentions in view of their superb thermal stability. However, unavoidable defects near the perovskite surface seriously hampers carrier transport and easily results in ion accumulation at the interface of perovskite layer and charge transport layer. Herein, delocalized thiazole and imidazole derivatives iodide salts functionalized on perovskite surface have been investigated comprehensively. These two salts post-treatment on perovskite could efficiently passivate traps arising from Cs+ or I− vacancies. Additionally, these highly п-conjugated delocalized molecules can contribute to the efficient charge transport and prevent ions accumulation at the interface. As a result, sulfur-contained aminothiazolium iodide (ATI) post-treated CsPbI2Br devices showed simultaneous enhanced current density and voltage due to its higher interaction with perovskite lattice, this led to a champion efficiency of 13.91% with superb fill factor of more than 80%, which exhibited dramatic enhancement compared with the control samples (10.12%). Furthermore, surface passivation with delocalized molecules could effectively stabilize CsPbI2Br phase at room temperature or 80 °C annealing in ambient condition (65% RH). Equally important, this surface passivation allowed competitive efficiency of 11.26% with a large-area device (1.00 cm2). This high kill tolerant approach provide a new route to fabricate inorganic perovskite devices with higher efficiency and stability.
Delocalized molecule surface modification on CsPbI2Br film surface. Delocalized organic agents with ammonium functionalities (-NH3+) were post-treated on CsPbI2Br film for surface passivation, which resulted in larger grains with reduced trap densities. Delocalized п-electrons in molecules also contributed to the more rapid carrier transfer at the interface. As s result, a much-enchaned efficiency of 13.91% with superb fill factor of 80.81% upon thiazole iodide salts treatment was achieved. Stability of perovskite devices with encapsulation under room temperature and 80°C annealing was enhanced significantly. Furthermore, competitive performance of CsPbI2Br perovskite devices with large active area was achieved.
The polyelectrolyte‐doped SnO2 film can efficiently improve the perovskite solar cell (PSC) performance and stability. Compared with the pristine SnO2 film, the better energy level alignment, larger built‐in field, enhanced electron transfer/extraction, and reduced charge recombination all contribute to the improved device performance. Finally, a power conversion efficiency of 20.61% is successfully achieved for the PSC prepared under low temperature.
The charge transport layer is crucial to the performance and stability of the perovskite solar cells (PSCs). Compared with other conventional metal oxide electron transport materials, SnO2 has a deeper conduction band and higher electron mobility, and can efficiently serve as an electron transport layer to facilitate charge extraction and transfer. Herein, an optimized low‐temperature solution‐processed SnO2 electron transport layer is achieved by doping polyethylenimine polyelectrolyte into SnO2 for the first time in the PSCs. It is found that the performance of all aspects of the doped SnO2 film is improved over that of the pristine SnO2 film. The better energy level alignment, larger built‐in field, enhanced electron transfer/extraction, and reduced charge recombination all contribute to the improved device performance. Finally, a PSC with a power conversion efficiency of 20.61% is successfully prepared under low temperature below 150 °C. Moreover, the stability of the doped SnO2‐based device is also greatly improved.
The mechanism of current shunting in flexible Cu2Zn1−x Cd x Sn(S,Se)4 solar cells is studied. The results demonstrate that partial Cd substitution of Zn can significantly minimize the loss of parallel current (ohmic current, weak diode current, and space‐charge limited current) and enhance fill factor, resulting in a significant improvement in device repeatability (with best efficiency of 6.49%).
Partial cation substitution is an effective way to inhibit defects and carrier recombination, which can improve the efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Herein, flexible Cu2Zn1−x Cd x Sn(S,Se)4 (x = 0–15%) solar cells are fabricated on Mo foils with partial Cd substitution for Zn via a green solution‐process. The best device performance can be achieved when Cd/(Zn + Cd) = 8%, with an efficiency up to 6.49% and a significantly improved device repeatability. The E U decreases from 24 to 15 meV, indicating that antisite defects and band tailings are effectively suppressed. C–V data reveal that W d and V bi are enhanced after doping Cd, resulting in a stronger built‐in electric field which facilitates Fermi‐level splitting and hence increases band bending of the absorber toward the junction interface. Furthermore, the mechanism of current shunting is studied using an equivalent circuit model with three parallel current pathways to fit J–V curves. The key parameters for the solar cell diode such as A, J 0, and R sh are significantly improved by partially substituting Zn with Cd, demonstrating that current shunting loss is suppressed and the junction quality is improved, resulting in a significant improvement in device repeatability.
High‐quality Cu2O thin films are synthesized by a facile solution method and the Cu2O/Si heterojunction solar cells are fabricated, showing an outstanding photovoltaic performance. Significantly, the photovoltaic conversion efficiency of Cu2O/Si solar cells can be greatly improved to a record value of 9.54% by sequential interfacial engineering.
Cuprous oxide (Cu2O) is a nontoxic and earth‐abundant semiconductor material, which is a promising candidate for low‐cost photovoltaic applications. Although Cu2O‐based solar cells have been studied for a few decades, they still suffer from disappointing photovoltaic performance due to its high trap‐state density and inferior carrier collection efficiency. Herein, a facile solution method is demonstrated to synthesize high‐quality Cu2O films with low defects as hole transport layers (HTLs) and the Cu2O/Si heterojunction solar cells are fabricated. Moreover, a variety of interfacial engineering and light management strategies are adopted to push the efficiency limit of Cu2O/Si solar cells, including a Ag transparent conductive layer, HNO3 passivation, Mg electrode back contact, and MoO x antireflection layer, which enable the boosting of carrier separation and reduce the loss of incident solar light, yielding a record high power conversion efficiency of 9.54%. This work may pave the way for economical and environment‐friendly use of Cu2O/Si heterojunction solar cells in daily life.
Poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) is doped with 0.025 mol% molecular organic Lewis acid bis(pentafluorophenyl)zinc, which exhibits higher hole mobility and well‐matched energy. An enhanced highest power conversion efficiency of 17.49% is achieved for a perovskite solar cell based on doped P3HT without destroying its stability.
The molecular organic Lewis acid bis(pentafluorophenyl)zinc [Zn(C6F5)2] is reported as an efficient p‐type dopant for poly(3‐hexylthiophene‐2,5‐diyl) (P3HT), to be used as hole‐transporting material (HTM) in perovskite solar cells (PSCs) for the first time. To date, the most efficient PSCs use lithium bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) and 4‐tert‐butylpyridine (tBP) as standard additives for HTMs. However, such dopants can induce deleterious effects on device stability. Herein, the effect of the concentration of Zn(C6F5)2 in P3HT HTM on the performance of PSCs is investigated. The P3HT‐based PSCs using a low concentration of the dopant (0.025 mol%) in the HTM layer exhibit the best performance and the highest power conversion efficiency (PCE) of 17.49%, which is almost 3.5% higher than the achieved PCE for pristine P3HT‐based PSCs. The origin of the improved performance for PSCs is further investigated, by studying the conductivity and hole mobility of the thin films based on pristine and doped P3HT. Adding a small amount of Zn(C6F5)2 to P3HT increases its thin‐film hole mobility and its hole extraction ability.
The formation of nanocrystals in quasi‐2D Ruddlesden–Popper perovskite can be spontaneously induced by appropriately timed anti‐solvent treatment, as reported by Aleksandra B. Djurišić, Kam Sing Wong, and co‐workers in article number https://doi.org/10.1002/adom.2019002691900269. Only nanocrystals with n = 4 phase are detected, different from commonly obtained mixtures of different phases. The formation of nanocrystals in a disordered matrix results in a significant enhancement of the light emission due to defect passivation.
Back contact between [6,6]‐phenyl‐C61‐butyric acid methyl ester and metal electrode cathode in planar perovskite solar cell is modified via molecule Isatin, resulting in multiple beneficial effects, e.g., enhanced charge mobility, lower charge transfer resistance, higher charge conductivity, reduced energy barrier, and protective layer effect.
The cathode interface plays a critical role in achieving high‐performance fullerene/perovskite planar solar cells. Herein, the simple molecule Isatin and its derivatives are introduced at the back contact [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM)/Al as a cathode modification interlayer. It is revealed that the Isatin interlayers facilitate electron transport/extraction and suppress electron recombination, attributed to the formation of negative dipole potential steps and the passivation of the interfacial trap density. The average power conversion efficiencies of the resulting devices are significantly improved by 11% from 17.68% to 19.74%, with an enhancement in all device parameters including short‐circuit current, open‐circuit voltage, and fill factor. The hysteresis index is found to disappear. In addition, such interlayer enhances device stability under ambient conditions compared to the control devices due to suppression of moisture‐induced degradation of the perovskite films. These findings provide a comprehensive understanding of the engineering of the back contact between PCBM and the metal electrode to improve efficiency and stability of perovskite solar cells.
Single‐crystalline 2D Ruddlesden–Popper‐type halide perovskites (RPPs) are demonstrated to exhibit extremely large two‐photon absorption coefficients in the near‐IR due to near‐resonance with 2D excitons. Efficient polarization‐resolved sub‐bandgap photodetection is realized at room temperature by utilizing 2D‐RPP two‐photon detectors, which opens avenues for future exploration of nonlinear optics in this class of hybrid quantum materials.
Two‐dimensional (2D) perovskites have proved to be promising semiconductors for photovoltaics, photonics, and optoelectronics. Here, a strategy is presented toward the realization of highly efficient, sub‐bandgap photodetection by employing excitonic effects in 2D Ruddlesden–Popper‐type halide perovskites (RPPs). On near resonance with 2D excitons, layered RPPs exhibit degenerate two‐photon absorption (D‐2PA) coefficients as giant as 0.2–0.64 cm MW − 1. 2D RPP‐based sub‐bandgap photodetectors show excellent detection performance in the near‐infrared (NIR): a two‐photon‐generated current responsivity up to 1.2 × 104 cm2 W−2 s−1, two orders of magnitude greater than InAsSbP‐pin photodiodes; and a dark current as low as 2 pA at room temperature. More intriguingly, layered‐RPP detectors are highly sensitive to the light polarization of incoming photons, showing a considerable anisotropy in their D‐2PA coefficients (β[001]/β[011] = 2.4, 70% larger than the ratios reported for zinc‐blende semiconductors). By controlling the thickness of the inorganic quantum well, it is found that layered RPPs of (C4H9NH3)2(CH3NH3)Pb2I7 can be utilized for three‐photon photodetection in the NIR region.
The high‐performing single‐junction organic solar cell blend, PM6:Y6, is examined to obtain an in‐depth understanding of the voltage losses, and charge recombination and extraction dynamics. The devices exhibit remarkable extraction coupled with moderate recombination losses. This behavior can most likely be credited to a beneficial morphology as evidenced by atomically resolved 19F magic‐angle‐spinning solid‐state NMR analysis.
The highly efficient single‐junction bulk‐heterojunction (BHJ) PM6:Y6 system can achieve high open‐circuit voltages (V OC) while maintaining exceptional fill‐factor (FF) and short‐circuit current (J SC) values. With a low energetic offset, the blend system is found to exhibit radiative and non‐radiative recombination losses that are among the lower reported values in the literature. Recombination and extraction dynamic studies reveal that the device shows moderate non‐geminate recombination coupled with exceptional extraction throughout the relevant operating conditions. Several surface and bulk characterization techniques are employed to understand the phase separation, long‐range ordering, as well as donor:acceptor (D:A) inter‐ and intramolecular interactions at an atomic‐level resolution. This is achieved using photo‐conductive atomic force microscopy, grazing‐incidence wide‐angle X‐ray scattering, and solid‐state 19F magic‐angle‐spinning NMR spectroscopy. The synergy of multifaceted characterization and device physics is used to uncover key insights, for the first time, on the structure–property relationships of this high‐performing BHJ blend. Detailed information about atomically resolved D:A interactions and packing reveals that the high performance of over 15% efficiency in this blend can be correlated to a beneficial morphology that allows high J SC and FF to be retained despite the low energetic offset.
In article number https://doi.org/10.1002/adma.2019036491903649, Xiaotian Hu, Wei Ma, Yiwang Chen, and co‐workers report a general approach to upscale flexible organic photovoltaics to the module scale without obvious efficiency loss by calculating the shear impulse during the coating/printing process. Photoelectric conversion efficiencies of 9.77% for a 1 cm2 single chip and 8.90% for a 15 cm2 solar module are demonstrated. The mechanics of shear impulse link the spin‐coating and slot‐die printing like a small boat overcoming the obstacles of thousands of mountains to arrive at a large‐area printing ferry. This research method also opens up a new strategy of lab‐to‐manufacturing translation for organic optoelectronic devices.
Infrared colloidal quantum dot (IR CQD) solar cells harvest solar power beyond the band edge of crystalline silicon. Using single lead halides for ligand exchange improves IR CQD passivation or transport, but not both. A mixed halide ligand exchange method improves both metrics, resulting in IR solar cells with improved power conversion efficiencies.
Infrared‐absorbing colloidal quantum dots (IR CQDs) are materials of interest in tandem solar cells to augment perovskite and cSi photovoltaics (PV). Today's best IR CQD solar cells rely on the use of passivation strategies based on lead iodide; however, these fail to passivate the entire surface of IR CQDs. Lead chloride passivated CQDs show improved passivation, but worse charge transport. Lead bromide passivated CQDs have higher charge mobilities, but worse passivation. Here a mixed lead‐halide (MPbX) ligand exchange is introduced that enables thorough surface passivation without compromising transport. MPbX–PbS CQDs exhibit properties that exceed the best features of single lead‐halide PbS CQDs: they show improved passivation (43 ± 5 meV vs 44 ± 4 meV in Stokes shift) together with higher charge transport (4 × 10‐2 ± 3 × 10‐3 cm2 V‐1 s‐1 vs 3 × 10‐2 ± 3 × 10‐3 cm2 V‐1 s‐1 in mobility). This translates into PV devices having a record IR open‐circuit voltage (IR V oc) of 0.46 ± 0.01 V while simultaneously having an external quantum efficiency of 81 ± 1%. They provide a 1.7× improvement in the power conversion efficiency of IR photons (>1.1 µm) relative to the single lead‐halide controls reported herein.
Intrinsic strong linear dichroism of a newly‐tailored 2D hybrid perovskite enables remarkable polarized‐light photoelectric detection behaviors, including quite fast response time (300 μs), notable photocurrent on/off ratio (>103) and large dichroic ratios (I pb/I pc ≈ 1.20 at 520 nm, 1.23 at 637 nm).
Linear dichroism of 2D materials is brought into practical operation of polarized light detection; currently, organic–inorganic 2D hybrid perovskites with the linear dichroic nature offers immense potentials within this portfolio. Here, a newly tailored 2D hybrid perovskite, (iBA)2(MA)Pb2I7 (1, where MA+ is methylammonium and iBA+ is n‐isobutylammonium) is investigated, adopting a highly anisotropic bilayered perovskite motif that results in strong crystallographic‐dependence of linear dichroism. Both the absorption spectra (300–650 nm) and polarized‐sensitive activities of 1 exhibit the distinctive anisotropic characteristics. Consequently, based on this intrinsic linear dichroism, crystal‐based photodetectors of 1 show remarkable polarized‐light detecting behaviors, including quite fast response time (≈300 µs), notable photocurrent on/off ratio (>103) and large dichroic ratios (I pb/I pc ≈ 1.20 at 520 nm, 1.23 at 637 nm). Such figure‐of‐merits are comparable to those of the conventional GeSe nanoflakes (the linearly dichroic ratio of ≈1.09 at 532 nm), revealing the great potentials of 1 for the future polarized photodetection. As an innovative work, the intrinsic anisotropy and prominent linear dichroism of 1, together with the structural flexibility, opens up a promising avenue for exploring new candidates for the 2D polarized optoelectronic applications.
The filterless polarization‐sensitive narrowband photodetectors based on 2D perovskite (iso‐BA)2PbI4 are demonstrated with simultaneously wavelength discrimination and polarization selection. The photodetector shows a linear dichroic ratio of 1.56 at 552 nm, the full width at half maximum of 20 nm an external quantum efficiency of 120% and a specific detectivity of 1.23 × 1010 Jones under the normal incidence.
Polarization‐sensitive narrowband photodetectors can respond to a narrow spectral range of light together with the ability to sense the polarization of light. Traditionally, expensive filters combined with polarizers are utilized to realize the polarization‐sensitive narrowband photodetections. To reduce the cost and simplify optical system, here a polarization‐sensitive narrowband photodetector based on 2D perovskite single crystals without any additional optical components is reported. The photodetector shows a linear dichroic ratio of 1.56 at 552 nm under the oblique incident angle of 45° and the full width at half maximum of 20 nm. Moreover, the photodetector exhibits a high external quantum efficiency of 120% and a peak specific detectivity of 1.23 × 1010 Jones under the normal illumination. This polarization‐sensitive narrowband photoresponse can be ascribed to the charge collection narrowing mechanism assisted by the enhanced self‐trapped states in 2D perovskites and the large anisotropic crystal structure between different crystal directions. In particular, the device configuration is specially designed so that the absorption anisotropy takes place between the in‐plane and out‐of‐plane directions and photogenerated carriers transport along the in‐plane direct to avoid the large organic barrier along the out‐of‐plane direction, resulting in the polarization‐sensitive narrowband photodetections with high performance.
Perovskite solar cells suffer from limited long‐term stability, which is currently an obstacle for using them for efficient solar energy conversion. Bias‐dependent degradation mechanisms in perovskite solar cells are studied utilizing concentrated natural sunlight, revealing different dominant mechanisms under different bias conditions. Understanding the degradation mechanism(s) dominant at the cell's operating conditions yields routes to eliminate or reduce them.
Degradation rates in perovskite solar cells (PSCs) were previously shown to be bias dependent; however, little is known about the mechanisms and driving factors that account for such degradation. Herein, stability studies under concentrated sunlight are demonstrated as a powerful experimental methodology to investigate bias‐dependent PSC degradation mechanisms. Stress testing of encapsulated PSCs' stability shows that light intensity is more significant than the illumination dose for PSC degradation under short‐circuit (SC) conditions, whereas the dose is the determining factor under open‐circuit (OC) stressing. This indicates that different degradation mechanisms are dominant under different bias conditions. It is postulated that degradation at SC biasing is dominated by ion migration, facilitated by photogenerated defects. Degradation at OC biasing can be explained by photogenerated radicals acting as nonradiative recombination centers (charge traps), which are created via reactions with accumulated charge carriers. Trap formation upon OC biasing is in accordance with degradation of photoluminescence and OC voltage (V OC) observed under this stress. A combination of multiple mechanisms, all with reduced driving forces compared with OC /SC biasing, explains degradation at maximum power point biasing. Understanding the bias effect on PSC stability can elucidate the underlying degradation mechanisms and lead to routes to reduce them.
Atomic layer deposition (ALD) is key to improving the efficiency and stability of perovskite solar cells (PSCs). Moreover, ALD unlocks novel options regarding device architecture and processing, not achievable otherwise. Herein, the state of the art in ALD‐grown functional charge transport layers for PSCs is highlighted and the most urgent scientific issues and opportunities for further research are outlined.
Within less than a decade of development, perovskite solar cells (PSCs) have reached efficiency levels that trigger the question about commercialization of the technology. However, the steadily increasing efficiency of PSCs is still accompanied by concerns of long‐term stability and open questions about upscaled manufacturing. Atomic layer deposition (ALD) is a technique that can provide unique contributions to both issues. On top of that, ALD is an enabling technology to unlock novel options regarding device architecture and processing that are not achievable by other coating techniques. As such, ALD has enjoyed some notable recent interest from the community of perovskite photovoltaics. Herein, the current state of the art in ALD‐grown functional charge transport layers for PSCs is highlighted. The most urgent scientific issues that have to be tackled are emphasized and opportunities for further research are outlined.
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In article number https://doi.org/10.1002/adma.2019032391903239, Junsheng Yu, Wei Huang, Ziyi Ge, Tobin J. Marks, Antonio Facchetti, and co‐workers present a spontaneous passivation method to greatly improve the performance of perovskite solar cells (PSCs) by using a zwitterionic small‐molecule electrolyte. This bottom‐up passivation is a novel and promising strategy to overcome outstanding issues impeding PSC advances in the future.
