Improvement Of Carrier Lifetime Research Articles

N‐methyl‐2‐pyrrolidone Iodide as Functional Precursor Additive for Record Efficiency 2D Ruddlesden‐Popper (PEA)2(Cs)n−1PbnI3n+1 Solar Cells

Abstract2D perovskite (PEA)2(Cs)n−1PbnI3n+1 (PEA: phenylethylammonium) exhibits more strengthened phase stability than its 3D components under ambient conditions and hence gained great attention in recent years. However, uncontrollable crystallization kinetics in (PEA)2(Cs)n−1PbnI3n+1 leads to difficulty in controlling film morphology and phase‐orientation regulation, resulting in poor power conversion efficiency (PCE). Herein, by incorporating precursor additive N‐methyl‐2‐pyrrolidone iodide (NMPI), the crystallization rate during the deposition of (PEA)2(Cs)n−1PbnI3n+1 film is efficiently regulated. As a result, the 2D or quasi‐2D perovskite solar cell (PSC) delivers record PCEs in all reported 2D or quasi‐2D CsPbX3 families, for instance, the quasi‐2D (n = 20) CsPbI3 PSC exhibits a record PCE of 14.59%, showing significantly enhanced stability. Detailed characterization reveals that the NMPI forms hydrogen bonds with dimethylammonium iodide (DMAI) in the precursor to control crystallization rate for a smooth morphology with small fluctuation, which leads to improved carrier lifetime and reduced trap‐density. More importantly, femtosecond transient absorption (fs‐TA) measurements confirm an improved phase purity and the suppressed nonradiative recombination in quasi‐2D perovskite film. It is believed that this simple additive strategy paves a new route for solving phase transition and crystallization kinetic problems in 2D and quasi‐2D CsPbX3.

Improving the Photovoltage of Blade-Coated MAPbI3 Perovskite Solar Cells via Surface and Grain Boundary Passivation with π-Conjugated Phenyl Boronic Acids.

High-density electronic defects at the surfaces and grain boundaries (GBs) of perovskite materials are the major contributor to suppressing the power conversion efficiency (PCE) and deteriorating the long-term stability of the solar devices. Hence, the judicious selection of chemicals for the passivation of trap states has been regarded as an effective strategy to enhance and stabilize the photovoltaic performance of solar devices. Here, we systematically investigated the passivation effects of four organic π-conjugated phenylboronic acid molecules: phenylboronic acid, 2-amino phenylboronic acid (2a), 3-amino phenylboronic acid (3a), and 4-amino phenylboronic acid (4a) by adding them into the methylammonium lead iodide (MAPbI3) precursor solution. We found that solar devices with an optimized 5% (mol %) 3a treatment achieve the best passivation effect due to the strong cross-linking ability via hydrogen bonding interactions between the I of the [PbI6]4- octahedral network of perovskite films and the cross-linking terminal groups [-B(OH)2, (-NH2)] of 3a. Moreover, the lone pair of electrons on the N atom of an amino group of 3a can passivate the uncoordinated Pb2+ defects at the surface/GBs. As a result, the 3a-passivated device shows a high open-circuit voltage of 1.13 V, which is a 14.1% improvement compared to the control device (0.99 V). Moreover, the reduced defect density and improved carrier lifetimes enabled a high PCE of 18.89% in our blade-coated champion inverted structure of MAPbI3 solar cells, with improved long-term stability.

Unveiling Roles of Tin Fluoride Additives in High‐Efficiency Low‐Bandgap Mixed Tin‐Lead Perovskite Solar Cells

AbstractLow‐bandgap mixed tin–lead perovskite solar cells (PSCs) have been attracting increasing interest due to their appropriate bandgaps and promising application to build efficient all‐perovskite tandem cells, an effective way to break the Shockley–Queisser limit of single‐junction cells. Tin fluoride (SnF2) has been widely used as a basis along with various strategies to improve the optoelectronic properties of low‐bandgap SnPb perovskites and efficient cells. However, fully understanding the roles of SnF2 in both films and devices is still lacking and fundamentally desired. Here, the functions of SnF2 in both low‐bandgap (FASnI3)0.6(MAPbI3)0.4 perovskite films and efficient devices are unveiled. SnF2 regulates the growth mode of low‐bandgap SnPb perovskite films, leading to highly oriented topological growth and improved crystallinity. Meanwhile, SnF2 prevents the oxidation of Sn2+ to Sn4+ and reduces Sn vacancies, leading to reduced background hole density and defects, and improved carrier lifetime, thus largely decreasing nonradiative recombination. Additionally, the F− ion preferentially accumulates at hole transport layer/perovskite interface with high SnF2 content, leading to more defects. This work provides in‐depth insights into the roles of SnF2 additives in low‐bandgap SnPb films and devices, assisting in further investigations into multiple additives and approaches to obtain efficient low‐bandgap PSCs.

Geometric optimization and performance enhancement of PEDOT: PSS/GaAs NP array based heterojunction solar cells

Polymer/semiconductor nanostructure array based solar cells (SCs) exhibit extremely low optical losses, excellent light-harvesting, improved carrier lifetime, increased defect tolerance etc. and can be a new pathway for low-cost high efficiency SCs. In order to fabricate efficient heterojunction SCs, it is extremely necessary to evaluate their optimal geometric configuration theoretically. In this article, using 3D-finite difference time domain (FDTD) method, we have optimized the geometric configuration of poly (3, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) coated vertically aligned GaAs Nano pyramid (NP) array heterojunction SCs to obtain high average optical absorption and J sc of 92.2% and 41.1 mA/cm 2 , respectively. The optimized structure simulated in Lumerical Charge Solver DEVICE module, exhibit power conversion efficiency (PCE) of 15.9% despite low carrier mobility and lifetime of 1000 cm 2 v −1 s −1 and 2ns respectively. • Role of GaAs nanopyramids (NPs) in efficient light harvesting is studied. • Optimization of geometrical dimensions of the NPs is performed in terms of optical J sc . • Conformal coating of PEDOT:PSS results in absorption enhancement. • GaAs NPs/PEDOT PSS based solar cells exhibits PCE of ~13%.

Surface Passivation Studies of n-type Crystalline Silicon for HIT Solar Cells

Surface passivation of n-type Crystalline Silicon wafer using thin dielectric films is an important and major factor in improving photovoltaic performance of HIT solar cells. In this study, Numerical simulation was carried out by using AFORS-HET simulation software in which energy band diagram with and without surface passivation (a-Si:H(i)) was investigated and the highest conduction band offset obtained on n type c-Si wafer is 0.85 eV which is comparatively higher than p-type c-Si wafer which was reported between 0.1 and 0.15 eV. Performance of HIT solar cell with passivation layer is simulated and obtained efficiency of 12.9% by incorporating actual conditions to compare with experimentally obtained data. It has been understood that applying an effective dielectric passivation of silicon surface resulted with high open circuit voltage (Voc) and low surface recombination lead to an increase of cell efficiency by 1.1% (from 11.8 to 12.9%). Also, the simulated results shows that to obtain good conversion efficiency Defect density of interface (Dit) should be lower than 1x1011 cm−2eV−1. Validation of the simulation results is done by conducting PECVD experiments for optimizing the amorphous silicon passivation to a layer thickness down to 15 nm. HIT Solar cells have been developed, using the optimum layer of passivation, and their performance have been studied. An improvement in the minority charge carrier lifetime of ~53 µs (from 215 to 268 μs) and on the other hand reduction in the surface recombination velocity of ~ 12.9 cm/s (from 65.11 cm/s down to 52.23 cm/s) has been achieved through passivation which effectively increased the open circuit voltage (Voc) from 0.690 to 0.705 V. In this preliminary study, a conversion efficiency of 11.3% of heterojunction with intrinsic thin layer (HIT) solar cell on 10 mm × 10 mm n-c-Si wafer has been obtained.

Ternary organic solar cells with PCEs of up to 16.6% by two complementary acceptors working in alloy-like model

Nowadays, improving the power conversion efficiency (PCE) of organic solar cells (OSCs) is still the most concerned issue. Ternary strategy can effectively improve the PCE while maintaining the single junction device structure from well-developed material systems. Herein, a brominated non-fullerene acceptor of ITC-2Br1 is used as the third component to optimize the efficient PM6:Y6 binary system with highly complementary absorption and higher LUMO value as compared with Y6. With 15% wt ITC-2Br1 in the ternary system, the device achieved a best PCE of 16.6%, which is significantly higher than that of its binary counterpart (15.6%). Through the study of neat and blend films, it is found that ITC-2Br1 and Y6 show good miscibility and the absorption of ternary blend film almost cover the whole range from visible and near-IR regions. The optimized ternary device shows an alloy-like working model with improved carrier lifetime and enhanced charge collection efficiency. This work provides a good example for the third component selection in ternary system, and the ternary strategy is a facile and effective method to boost the device performance of OSCs. • A SMA of ITC-2Br1 is used as the third component to optimize the PM6:Y6 binary system. • The absorption of ternary blend film almost cover the whole range from visible and near-IR regions. • With 15% wt ITC-2Br1 in the ternary system, PCE increased from 15.63% to 16.6%. • The better PCE for ternary device coincides with improved carrier lifetime and enhanced charge collection efficiency.

Quantum Dot Enabled Perovskite Thin Film with Enhanced Crystallization, Stability, and Carrier Diffusion via Pulsed Laser Nanoengineering

AbstractThe temperature control at the material interface, such as grain boundaries, is critical for defect density, and phases, which are important for high‐performance perovskite‐based optoelectronic devices. However, it is challenging to fine‐tune the microstructures in perovskite films with well‐controlled grain structure, interface defects, porosity, phase structure, and strains, simultaneously. Here, pulsed laser technology is combined with carbon quantum dots (CQDs) into perovskite absorbers with pore‐free, less defect, high crystallinity, enhanced absorption, low stress, and phase‐stabilized microstructures. Due to laser–CQD interaction‐induced grain boundary microstructure changes, perovskite films can be fabricated with much larger grains (>10 times) than those after thermal annealing. As CQDs are embedded to passivate grain, this leads to reduced grain boundary barrier at the interface, which significantly improve the carrier transportation in perovskite films. The shift of perovskite band to vacuum energy level leads to remarkable improvement of carrier extraction efficiency and lifetime, leading to much higher mobility of photogenerated carriers and diffusion length (>1 μm). The laser‐induced thermomechanical momentum significantly enhances crystal interface with hydrophobic perovskite film, resulting in much less residual tensile stress by 20 times and excellent stability. Pulsed‐laser‐assisted QD additive engineering has great potential for perovskites films under harsh conditions.

Ink Engineering of Inkjet Printing Perovskite.

Inkjet printing method is one of the most effective ways for fabricating large-area perovskite solar cells (PSCs). However, because ink crystallizes rapidly during printing, the printed perovskite film is discontinuous with increasing defects. It severely restricts the application of the inkjet printing technology to the fabrication of perovskite photovoltaic devices. Here, we designed a new mixed-cation perovskite ink system that can controllably retard the crystallization rate of perovskite. In this new ink system, the printing solvent is composed of n-methyl pyrrolidone (NMP) and dimethyl formamide (DMF), and PbX2 is replaced by PbX2-DMSO (X = Br, I) complex as a printing precursor to create a high-quality perovskite layer. Accordingly, the printed Cs0.05MA0.14FA0.81PbI2.55Br0.45 perovskite film exhibited high homogeneity with a large grain size (over 500 nm). Besides, the printed perovskite film possessed lower defects with improved carrier lifetime compared to the control sample. Combining these advantages, the printed PSC delivers decent power conversion efficiencies (PCEs) of 19.6% (0.04 cm2) and 17.9% (1.01 cm2). The large-area device can still retain its original efficiency of 89% when stored in air with humidity less than 20% for 1000 h.

Band-Structure Engineering of ZnxCd1−xSySe1−y Quaternary Alloys as the Window Layer for CdTe Solar Cells

With the optimization of the back contact, improvement of carrier lifetime, and the use of $\mathrm{Se}$-alloyed $\mathrm{Cd}\mathrm{Te}$ as the absorber, the power conversion efficiency (PCE) of $\mathrm{Cd}\mathrm{Te}$ solar cells has now risen beyond 22%. However, further improvement of the PCE of $\mathrm{Cd}\mathrm{Te}$-based solar cells by optimization of the window layer has not been fully discussed. In this work, we propose that ${\mathrm{Zn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ alloys can be tuned as promising window layers of both $\mathrm{Cd}\mathrm{Te}$ and ${\mathrm{Cd}\mathrm{Se}}_{x}{\mathrm{Te}}_{1\text{\ensuremath{-}}x}$ solar cells when band alignment and lattice match are taken into account. Using first-principles calculations and the special quasirandom structure approach, we investigate the compositional dependence of formation energies, lattice parameters, band-gap energies, and band alignments of ${\mathrm{Zn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ alloys. We find that the interaction parameters and thus the miscibility temperatures of ${\mathrm{Zn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ alloys are directly proportional to the lattice mismatch between the mixing elements, and are larger for mixed-cation alloys than for mixed-anion alloys. The lattice parameter of ${\mathrm{Zn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ exhibits a linear dependence to its composition. The bowing of band-gap energies of ${\mathrm{Zn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ alloys is quite large, due to the symmetry-reduction-induced intraband coupling in quaternary alloys. Finally, we illustrate the optimal composition range of ${\mathrm{Zn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ alloys as the window layer for both $\mathrm{Cd}\mathrm{Te}$ solar cells and ${\mathrm{Cd}\mathrm{Se}}_{x}{\mathrm{Te}}_{1\text{\ensuremath{-}}x}$ solar cells. Our work provides a guideline for further improving the performance of $\mathrm{Cd}\mathrm{Te}$ and ${\mathrm{Cd}\mathrm{Se}}_{x}{\mathrm{Te}}_{1\text{\ensuremath{-}}x}$ solar cells by adopting ${\mathrm{Zn}}_{x}{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ alloys as promising window layers.

Low‐Dimensional Contact Layers for Enhanced Perovskite Photodiodes

AbstractControlling defects and energy‐band alignments are of paramount importance to the development of high‐performance perovskite‐based photodiodes. Yet, concurrent improvements in interfacial contacts and defect reduction simply by tailoring bottom contacts have not been investigated. An effective strategy is reported that can simultaneously improve energy‐band alignments and structural defects by introducing low‐dimensional contact (LDC) layers at the bottom interface. It is found that LDC‐based perovskites considerably suppress undesirable structural defects induced by microstrains, resulting in reduced nonradiative recombination centers and improved carrier lifetimes. Additionally, the resulting LDC‐based interface structures help block minority carrier injection from the electrodes by forming built‐in electric fields. As a consequence, LDC‐based perovskite photodiodes showed improved light detection capabilities. The result opens an avenue to yield highly efficient photodiodes.

The effect of diffusion barrier on minority carrier lifetime improvement of seed assisted cast silicon ingot

A newly designed diffusion barrier (DB) was introduced to industrial silicon ingot casting with various seeding techniques, in order to reduce the height of bottom low lifetime region. The DB was fabricated by alternatively brushing silica and silicon nitride coatings with high purity on the inner bottom of the crucible. The effects of DB on mono-like (ML) and multicrystalline (assisted by chips and slabs) ingots were characterized and compared. The results showed that the DB had much stronger influence in mono-like ingot than in multicrystalline ingots. The related mechanism on ingot bottom lifetime improvement was discussed.

Critical role of interface contact modulation in realizing low-temperature fabrication of efficient and stable CsPbIBr2 perovskite solar cells

CsPbIBr2 perovskite solar cells (PSCs) have received considerable concern due to their excellent stability. However, the interface defects and imperfect band alignment between electron transporting layer (ETL) and perovskite is one of the main reasons for hindering further efficiency improvement. Herein, we modulate the band alignment and perovskite crystallization of the ETL/perovskite interface by employing ZnO and SnO2 as ETL, which exhibit high electron mobility and can be fabricated at low temperature. Both ZnO and SnO2-based devices were fabricated at low temperature below 160℃. First, the effect of ZnO and SnO2 on the performance of CsPbIBr2 PSCs is systematically investigated. SnO2-based PSCs show a higher power conversion efficiency (PCE) of 10.81% as a consequence of improved Voc and fill factor (FF) as compared to 9.70% of ZnO counterpart, which is attributed to improved band alignment and perovskite crystallization, leading to enhanced electron extraction, reduced interface nonradiative recombination and improved carrier lifetimes. Remarkably, SnO2 ETL can also reduce hysteresis and improve device stability as compared to ZnO ETL. The present study unveils the critical role of interface contact modulation of CsPbIBr2 PSCs and provides an insightful strategy for preparing efficient and stable low-temperature inorganic PSCs.

High-performing self-driven ultraviolet photodetector by TiO2/Co3O4 photovoltaics

Ultraviolet (UV) may provide the essential to maintain the human body and metabolism, however, excessive exposure to UV light is absolutely harmful. We may take advantage of the strong UV energy for energy conversion devices. A stable, simple and scalable heterojunction (TiO2/Co3O4) thin film was developed for UV-absorbing and visible-blind photovoltaic. Effective hole transport layer (HTL, NiO) insertion established photovoltaics, having a power conversion efficiency of 15.8%. The heterojunction exhibits the improved carrier lifetime from 1.94 ms to 9 ms, resulting in the enhancement of both photovoltage and photocurrent from 0.17 V to 0.78 V and from 0.54 mA cm−2 to 13.5 mA cm−2, respectively. The TiO2/Co3O4 device exhibits a photoresponse to a UV light intensity of 60 μW cm−2 in the presence of sunlight and works stable for over a year. The results indicate metal oxide heterojunction (TiO2/Co3O4) photovoltaic device could be useful for monitoring UV radiation exposure and cost-effective self-powered UV optoelectronics. The functional utilization of metal oxide layers would provide strong benefits for photoelectric devices, such as photodetectors and transparent solar cells.

Multifunctional Chemical Linker Imidazoleacetic Acid Hydrochloride for 21% Efficient and Stable Planar Perovskite Solar Cells.

Chemical interaction at a heterojunction interface induced by an appropriate chemical linker is of crucial importance for high efficiency, hysteresis-less, and stable perovskite solar cells (PSCs). Effective interface engineering in PSCs is reported via a multifunctional chemical linker of 4-imidazoleacetic acid hydrochloride (ImAcHCl) that can provide a chemical bridge between SnO2 and perovskite through an ester bond with SnO2 via esterification reaction and an electrostatic interaction with perovskite via imidazolium cation in ImAcHCl and iodide anion in perovskite. In addition, the chloride anion in ImAcHCl plays a role in the improvement of crystallinity of perovskite film crystallinity. The introduction of ImAcHCl onto SnO2 realigns the positions of the conduction and valence bands upwards, reduces nonradiative recombination, and improves carrier life time. As a consequence, average power conversion efficiency (PCE) is increased from 18.60% ± 0.50% to 20.22% ± 0.34% before and after surface modification, respectively, which mainly results from an enhanced voltage from 1.084 ± 0.012 V to 1.143 ± 0.009 V. The best PCE of 21% is achieved by 0.1 mg mL-1 ImAcHCl treatment, along with negligible hysteresis. Moreover, an unencapsulated device with ImAcHCl-modified SnO2 shows much better thermal and moisture stability than unmodified SnO2 .

Recombination and bandgap engineering in CdSeTe/CdTe solar cells

Selenium compositional grading in CdTe-based thin-film solar cells substantively improves carrier lifetime and performance. However, where and how recombination lifetime improves has not been studied significantly. Here, we deposit a CdSexTe1−x/CdTe bilayer on MgZnO/SnO2/glass, which achieves a short-circuit current density greater than 28 mA/cm2 and carrier lifetimes as long as 10–20 ns. We analyze the grain structure, composition, and recombination through the thickness of the absorber using electron backscatter diffraction, Auger-electron spectroscopy, cathodoluminescence spectrum imaging, and time-resolved photoluminescence microscopy. Despite small CdSeTe grains near the pn-junction and significantly larger CdTe grains in the rest of the film, both time-resolved photoluminescence and cathodoluminescence reveal that the carrier lifetime in CdSeTe alloy regions is longer than in CdTe regions. The results indicate that Se both passivates grain boundaries and improves grain-interior carrier lifetime. However, these effects occur only where there is significant alloying, which is important for bandgap engineering.

Highly Efficient and Stable Solar Cells Based on Crystalline Oriented 2D/3D Hybrid Perovskite.

Highly efficient and stable 2D/3D hybrid perovskite solar cells using 2-thiophenemethylammonium (ThMA) as the spacer cation are successfully demonstrated. It is found that the incorporation of ThMA spacer cation into 3D perovskite, which forms a 2D/3D hybrid structure, can effectively induce the crystalline growth and orientation, passivate the trap states, and hinder the ion motion, resulting in improved carrier lifetime and reduced recombination losses. The optimized device exhibits a power conversion efficiency (PCE) of 21.49%, combined with a high VOC of 1.16 V and a notable fill factor (FF) of 81%. More importantly, an encapsulated 2D/3D hybrid perovskite device sustains ≈99% of its initial PCE after 1680 h in the ambient atmosphere, whereas the control 3D perovskite device drops to ≈80% of the original performance. Importantly, the device stability under continuous light soaking (100 mW cm-2 ) is enhanced significantly for 2D/3D perovskite device in comparison with that of the control device. These results reveal excellent photovoltaic properties and intrinsic stabilities of the 2D/3D hybrid perovskites using ThMA as the spacer cation.

Effect of methylamine vapor exposure and ambient ageing on CsxMA1−xPbI3−xBrx perovskites for improved carrier collection

Caesium-methylammonium lead iodide-bromide perovskites (CsxMA1−xPbI3−xBrx) is interesting for stable and high-voltage tandem solar cells. Here, we report a systematic material and device study of CsxMA1−xPbI3−xBrx (x = 0, 5, 10 and 15%) perovskite films. Cs-Br incorporation reduces carrier lifetime of as-deposited films, from 21.5 μs for x = 0% to 5.8 μs for x = 15%. Unlike pure MA films, Cs-Br incorporated films were not only more resilient to degradation, their carrier lifetime increased by 50%–300% when exposed to ambient due to the humidity-assisted healing. The morphology of as-deposited films was poor. Methylamine vapor exposure (MVE) was used to improve the morphology and crystallinity, which further improved carrier lifetime up to 50 μs. Devices with efficiency >17% were fabricated on MVE treated Cs0.10MA0.90PbI2.90Br0.10 films. The short circuit current density was further increased by fabricating devices on ‘aged’ films which have higher lifetime due to humidity healing. Best Cs0.10MA0.90PbI2.90Br0.10 devices show good ambient stability with VOC and FF unchanged even after 5 days of ambient exposure.

Carrier Dynamics Engineering for High-Performance Electron-Transport-Layer-free Perovskite Photovoltaics

Summary Electron-transport-layer-free (ETL-free) device architectures are promising designs for perovskite photovoltaics because they offer simpler configurations, low cost, and convenience for versatile optoelectronics. However, the development of ETL-free photovoltaics is hindered by their low performance. Herein, we reveal that a low electron-injection rate at the ETL-free interface is responsible for the performance loss. Moreover, we demonstrate that improving carrier lifetimes in the perovskite films can remedy the poor carrier extraction at interfaces, enabling carrier collection efficiency in ETL-free photovoltaics to approach that in ETL-containing devices. Using perovskite films with microsecond carrier lifetimes, we obtained ETL-free devices with a power conversion efficiency (PCE) of 19.5%, nearly eliminated hysteresis, and good stability. Such a PCE value is comparable to that (20.7%) of the analogous ETL-containing photovoltaics. These results offer opportunities for ETL-free architecture designs in the perovskite photovoltaics family. More importantly, this research provides a general approach to improving the performance of photovoltaics with low-injection-rate interfaces.

Reduced-Dimensional α-CsPbX3 Perovskites for Efficient and Stable Photovoltaics

Summary Inorganic CsPbX3 perovskites have gained great attention owing to their excellent thermal stability and carrier transport properties. However, the power conversion efficiency (PCE) of solution-processed CsPbX3 perovskite solar cells is still far inferior to that of their hybrid analogues. Insufficient film thickness and undesirable phase transition are the two major obstacles limiting their device performance. Here, we show that by adopting a new precursor pair, cesium acetate (CsAc) and hydrogen lead trihalide (HPbX3), we were able to overcome the notorious solubility limitation for Cs precursors to fabricate high-quality CsPbX3 perovskite films with large film thickness (∼500 nm). We further introduced a judicious amount of phenylethylammonium iodide (PEAI) into the system to induce reduced-dimensional perovskite formation. Unprecedentedly, the resulting quasi-2D perovskites significantly suppressed undesirable phase transition and thus reduced the film's trap density. Following this approach, we reported a state-of-the-art PCE to date, 12.4%, for reduced-dimensional α-CsPbI3 perovskite photovoltaics with greatly improved performance longevity.

Type-II InAs/GaAsSb Quantum Dot Solar Cells With GaAs Interlayer

One of the primary challenges facing quantum dot (QD)-based intermediate band solar cells is the short lifetime of charge carriers (~1 ns). To investigate this, InAs QD/GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> quantum well (QW) solar cells (SCs) with a 2-nm GaAs interlayer between the QDs and QW were fabricated for x = 0, 0.08, 0.14, and 0.17, respectively. Time-resolved photoluminescence measurements demonstrated prolonged carrier lifetimes up to 480 ns for the type-II SCs with x ≥ 14%. This improvement in carrier lifetime is assigned to the GaAs interlayer that reduces the wavefunction overlap between the electrons accumulated in the QDs and holes in the QW, and hence limits the possible emission pathways. External quantum efficiency measurements were performed to analyze the SC performance. An order of magnitude improvement was observed in the QD region (900- 1200 nm) for the type-II SCs and is linked to the prolonged carrier lifetime.