Showing papers on "Solar cell published in 2017"

Silicon heterojunction solar cell with interdigitated back contacts for a photoconversion efficiency over 26

Abstract: The efficiency of silicon solar cells has a large influence on the cost of most photovoltaics panels. Here, researchers from Kaneka present a silicon heterojunction with interdigitated back contacts reaching an efficiency of 26.3% and provide a detailed loss analysis to guide further developments.

Review on dye-sensitized solar cells (DSSCs): Advanced techniques and research trends

Abstract: Dye-sensitized solar cell (DSSC) offers an efficient and easily implemented technology for future energy supply. Compared to conventional silicon solar cells, it provides comparable power conversion efficiency (PCE) at low material and manufacturing costs. DSSC materials such as titanium oxide (TiO 2 ) are inexpensive, abundant and innocuous to the environment. Since DSSC materials are less prone to contamination and processable at ambient temperature, a roll-to-roll process could be utilized to print DSSCs on the mass production line. DSSCs perform better under lower light intensities, which makes them an excellent choice for indoor applications. Due to the advancement of molecular engineering, colored and transparent thin films have been introduced to enhance the aesthetic values. Up to now, such benefits have attracted considerable research interests and commercialization effort. Here, this review examines advanced techniques and research trends of this promising technology from the perspective of device modeling, state-of-art techniques, and novel device structures.

Dye-sensitized solar cells for efficient power generation under ambient lighting

Abstract: Solar cells that operate efficiently under indoor lighting are of great practical interest as they can serve as electric power sources for portable electronics and devices for wireless sensor networks or the Internet of Things. Here, we demonstrate a dye-sensitized solar cell (DSC) that achieves very high power-conversion efficiencies (PCEs) under ambient light conditions. Our photosystem combines two judiciously designed sensitizers, coded D35 and XY1, with the copper complex Cu(II/I)(tmby) as a redox shuttle (tmby, 4,4′,6,6′-tetramethyl-2,2′-bipyridine), and features a high open-circuit photovoltage of 1.1 V. The DSC achieves an external quantum efficiency for photocurrent generation that exceeds 90% across the whole visible domain from 400 to 650 nm, and achieves power outputs of 15.6 and 88.5 μW cm–2 at 200 and 1,000 lux, respectively, under illumination from a model Osram 930 warm-white fluorescent light tube. This translates into a PCE of 28.9%. A dye-sensitized solar cell that has been designed for efficient operation under indoor lighting could offer a convenient means for powering the Internet of Things.

Stable high efficiency two-dimensional perovskite solar cells via cesium doping

Abstract: Two-dimensional (2D) organic–inorganic perovskites have recently emerged as one of the most important thin-film solar cell materials owing to their excellent environmental stability. The remaining major pitfall is their relatively poor photovoltaic performance in contrast to 3D perovskites. In this work we demonstrate cesium cation (Cs+) doped 2D (BA)2(MA)3Pb4I13 perovskite solar cells giving a power conversion efficiency (PCE) as high as 13.7%, the highest among the reported 2D devices, with excellent humidity resistance. The enhanced efficiency from 12.3% (without Cs+) to 13.7% (with 5% Cs+) is attributed to perfectly controlled crystal orientation, an increased grain size of the 2D planes, superior surface quality, reduced trap-state density, enhanced charge-carrier mobility and charge-transfer kinetics. Surprisingly, it is found that the Cs+ doping yields superior stability for the 2D perovskite solar cells when subjected to a high humidity environment without encapsulation. The device doped using 5% Cs+ degrades only ca. 10% after 1400 hours of exposure in 30% relative humidity (RH), and exhibits significantly improved stability under heating and high moisture environments. Our results provide an important step toward air-stable and fully printable low dimensional perovskites as a next-generation renewable energy source.

Searching for promising new perovskite-based photovoltaic absorbers: the importance of electronic dimensionality

Abstract: Searching for promising nontoxic and air-stable perovskite absorbers for solar cell applications has drawn extensive attention. Here, we show that a promising perovskite absorber should exhibit a high electronic dimensionality. Semiconductors that exhibit a high structural dimensionality, but a low electronic dimensionality have less promise as an absorber, because of barriers to isotropic current flow, enhanced electron/hole effective masses and fundamentally deeper defect states (more effective at causing recombination). Our concept accounts for the device performance of the perovskite-based solar cells reported in literature so far.

Progress on Perovskite Materials and Solar Cells with Mixed Cations and Halide Anions

Abstract: Organic–inorganic halide perovskite materials (e.g., MAPbI3, FAPbI3, etc.; where MA = CH3NH3+, FA = CH(NH2)2+) have been studied intensively for photovoltaic applications. Major concerns for the commercialization of perovskite photovoltaic technology to take off include lead toxicity, long-term stability, hysteresis, and optimal bandgap. Therefore, there is still need for further exploration of alternative candidates. Elemental composition engineering of MAPbI3 and FAPbI3 has been proposed to address the above concerns. Among the best six certified power conversion efficiencies reported by National Renewable Energy Laboratory on perovskite-based solar cells, five are based on mixed perovskites (e.g., MAPbI1–xBrx, FA0.85MA0.15PbI2.55Br0.45, Cs0.1FA0.75MA0.15PbI2.49Br0.51). In this paper, we review the recent progress on the synthesis and fundamental aspects of mixed cation and halide perovskites correlating with device performance, long-term stability, and hysteresis. In the outlook, we outline the future ...

Perovskite Solar Cells on the Way to Their Radiative Efficiency Limit – Insights Into a Success Story of High Open‐Circuit Voltage and Low Recombination

Abstract: Inorganic-organic lead-halide perovskite solar cells have reached efficiencies above 22% within a few years of research. Achieved photovoltages of >1.2 V are outstanding for a material with a bandgap of 1.6 eV - in particular considering that it is solution processed. Such values demand for low non-radiative recombination rates and come along with high luminescence yields when the solar cell is operated as a light emitting diode. This progress report summarizes the developments on material composition and device architecture, which allowed for such high photovoltages. It critically assesses the term "lifetime", the theories and experiments behind it, and the different recombination mechanisms present. It attempts to condense reported explanations for the extraordinary optoelectronic properties of the material. Amongst those are an outstanding defect tolerance due to antibonding valence states and the capability of bandgap tuning, which might make the dream of low-cost highly efficient solution-processed thin film solar cells come true. Beyond that, the presence of photon recycling will open new opportunities for photonic device design.

Extrinsic ion migration in perovskite solar cells

Abstract: The migration of intrinsic ions (e.g., MA+, Pb2+, I−) in organic–inorganic hybrid perovskites has received significant attention with respect to the critical roles of these ions in the hysteresis and degradation in perovskite solar cells (PSCs). Here, we demonstrate that extrinsic ions (e.g., Li+, H+, Na+), when used in the contact layers in PSCs, can migrate across the perovskite layer and strongly impact PSC operation. In a TiO2/perovskite/spiro-OMeTAD-based PSC, Li+-ion migration from spiro-OMeTAD to the perovskite and TiO2 layer is illustrated by time-of-flight secondary-ion mass spectrometry. The movement of Li+ ions in PSCs plays an important role in modulating the solar cell performance, tuning TiO2 carrier-extraction properties, and affecting hysteresis in PSCs. The influence of Li+-ion migration was investigated using time-resolved photoluminescence, Kelvin probe force microscopy, and external quantum efficiency spectra. Other extrinsic ions such as H+ and Na+ also show a clear impact on the performance and hysteresis in PSCs. Understanding the impacts of extrinsic ions in perovskite-based devices could lead to new material and device designs to further advance perovskite technology for various applications.

Stable 6%-efficient Sb 2 Se 3 solar cells with a ZnO buffer layer

Abstract: Sb2Se3, a binary compound containing non-toxic and Earth-abundant constituents, is a promising absorber material for low-cost, high-efficiency photovoltaics. Current Sb2Se3 thin-film solar cells use toxic CdS as the buffer layer and suffer from unsatisfactory stability. Here we selected ZnO as the buffer layer and constructed superstrate Sb2Se3 solar cells with a certified power conversion efficiency of 5.93%. Randomly oriented ZnO produced by spray pyrolysis induced the growth of Sb2Se3 with preferred [221] orientation, and hence resulted in devices with fewer interfacial defects and better efficiency. Moreover, our unencapsulated device survived the stringent damp-heat (85 ∘C, 85% humidity, 1,100 h), light-soaking (50 ∘C, 1.3 sun, 1,100 h), thermal cycling, and ultraviolet preconditioning tests. The combined features of stability, Earth-abundant constituent and potentially low-cost manufacturing highlight the great potential of Sb2Se3 solar cell as a possible non-toxic alternative to CdTe photovoltaics. Thin-film photovoltaic devices are often based on toxic or rare materials. Here, Wang et al. grow oriented Sb2Se3 thin film on a ZnO buffer layer, and fabricate solar cells with a certified 5.9% conversion efficiency and which pass harsh stability tests under humidity, heat and illumination.

Progress on lead-free metal halide perovskites for photovoltaic applications: a review

Abstract: Metal halide perovskites have revolutionized the field of solution-processable photovoltaics. Within just a few years, the power conversion efficiencies of perovskite-based solar cells have been improved significantly to over 20%, which makes them now already comparably efficient to silicon-based photovoltaics. This breakthrough in solution-based photovoltaics, however, has the drawback that these high efficiencies can only be obtained with lead-based perovskites and this will arguably be a substantial hurdle for various applications of perovskite-based photovoltaics and their acceptance in society, even though the amounts of lead in the solar cells are low. This fact opened up a new research field on lead-free metal halide perovskites, which is currently remarkably vivid. We took this as incentive to review this emerging research field and discuss possible alternative elements to replace lead in metal halide perovskites and the properties of the corresponding perovskite materials based on recent theoretical and experimental studies. Up to now, tin-based perovskites turned out to be most promising in terms of power conversion efficiency; however, also the toxicity of these tin-based perovskites is argued. In the focus of the research community are other elements as well including germanium, copper, antimony, or bismuth, and the corresponding perovskite compounds are already showing promising properties.

High Efficiency Near-Infrared and Semitransparent Non-Fullerene Acceptor Organic Photovoltaic Cells

Abstract: The absence of near-infrared (NIR) solar cells with high open circuit voltage (Voc) and external quantum efficiency (EQE) has impeded progress toward achieving organic photovoltaic (OPV) power conversion efficiency PCE > 15%. Here we report a small energy gap (1.3 eV), chlorinated nonfullerene acceptor-based solar cell with PCE = 11.2 ± 0.4%, short circuit current of 22.5 ± 0.6 mA cm–2, Voc = 0.70 ± 0.01 V and fill factor of 0.71 ± 0.02, which is the highest performance reported to date for NIR single junction OPVs. Importantly, the EQE of this NIR solar cell reaches 75%, between 650 and 850 nm while leaving a transparency window between 400 and 600 nm. The semitransparent OPV using an ultrathin (10 nm) Ag cathode shows PCE = 7.1 ± 0.1%, with an average visible transmittance of 43 ± 2%, Commission d’Eclairage chromaticity coordinates of (0.29, 0.32) and a color rendering index of 91 for simulated AM1.5 illumination transmitted through the cell.

Quantification of light-enhanced ionic transport in lead iodide perovskite thin films and its solar cell applications

Abstract: Ionic transport in organometal halide perovskites is of vital importance because it dominates anomalous phenomena in perovskite solar cells, from hysteresis to switchable photovoltaic effects. However, excited state ionic transport under illumination has remained elusive, although it is essential for understanding the unusual light-induced effects (light-induced self-poling, photo-induced halide segregation and slow photoconductivity response) in organometal halide perovskites for optoelectronic applications. Here, we quantitatively demonstrate light-enhanced ionic transport in CH3NH3PbI3 over a wide temperature range of 17–295 K, which reveals a reduction in ionic transport activation energy by approximately a factor of five (from 0.82 to 0.15 eV) under illumination. The pure ionic conductance is obtained by separating it from the electronic contribution in cryogenic galvanostatic and voltage-current measurements. On the basis of these findings, we design a novel light-assisted method of catalyzing ionic interdiffusion between CH3NH3I and PbI2 stacking layers in sequential deposition perovskite synthesis. X-ray diffraction patterns indicate a significant reduction of PbI2 residue in the optimized CH3NH3PbI3 thin film produced via light-assisted sequential deposition, and the resulting solar cell efficiency is increased by over 100% (7.5%–15.7%) with little PbI2 residue. This new method enables fine control of the reaction depth in perovskite synthesis and, in turn, supports light-enhanced ionic transport. Using light to excite ions in perovskite thin films can improve the conductivity and synthetic deposition of low-cost solar cells. Organometal halide perovskites have a suitable bandgap for photovoltaics and are compatible with solution processing, but tend to degrade after long exposure to sunlight. A team led by Qing Zhao from Peking University now reports that excited state ionic transport is the key to understanding perovskite’s poor photostability. Through video snapshots and quantitative conductivity extractions, their analysis revealed that illumination drops the energy barrier needed to activate ionic transport by almost five fold—an enhancement that may induce disorder of electronic structure in the solar cell over time. Intriguingly, the light-enhanced ionic transport can also catalyze removal of metal halide precipitates during thin film annealing in sequential deposition reaction, boosting the device efficiency from 7.5 to 15.7% after just 10 minutes of light exposure.

Photovoltaic Engineering Handbook

Abstract: TECHNOLOGICAL PROCESSES Solar cell technologies PHOTOVOLTAIC GENERATOR The photovoltaic generator Network of solar cells, modules, and arrays PHOTOVOLTAIC SYSTEMS ENGINEERING Storage batteries for photovoltaic power systems Electronic regulation Power conditioning Adaptation of a positive-displacement pump directly connected to a photovoltaic generator Centrifugal photovoltaic pumping CHARACTERIZATION AND TESTING METHODS International test procedures for photovoltaic modules Asian Institute of Technology photovoltaic module test bed system Testing of photovoltaic modules under natural conditions using the Asian Institute of Technology photovoltaic module test bed system Characterization procedure of photovoltaic refrigeration system Field trial procedure for a photovoltaic pumping system under natural conditions Battery-testing method for low-water-loss and starting, lighting, and ignition (automotive) batteries SIZING PROCEDURE The sizing of stand-alone photovoltaic power systems A dynamic simulation approach Prediction of photovoltaic system performance using cumulative frequency curves of irradiance ECONOMIC ANALYSIS Financial evaluation of renewable energy projects Comparative assessment of photovoltaics and handpumps for rural water supply Life-cycle cost comparison of alternative power supply for a portable pocket-sized stereo cassette tape recorder INSTRUMENTATION A simple metal-oxide-semiconductor field-effect transistor electronic variable load Equipment accommodation Terminology REFERENCES INDEX

Solution-Processed Nb:SnO2 Electron Transport Layer for Efficient Planar Perovskite Solar Cells

Abstract: Electron transport layer (ETL), facilitating charge carrier separation and electron extraction, is a key component in planar perovskite solar cells (PSCs). We developed an effective ETL using low-temperature solution-processed Nb-doped SnO2 (Nb:SnO2). Compared to the pristine SnO2, the power conversion efficiency of PSCs based on Nb:SnO2 ETL is raised to 17.57% from 15.13%. The splendid performance is attributed to the excellent optical and electronic properties of the Nb:SnO2 material, such as smooth surface, high electron mobility, appropriate electrical conductivity, therefore making a better growth platform for a high quality perovskite absorber layer. Experimental analyses reveal that the Nb:SnO2 ETL significantly enhances the electron extraction and effectively suppresses charge recombination, leading to improved solar cell performance.

Enhanced photovoltaic performance and stability with a new type of hollow 3D perovskite {en}FASnI3

Abstract: Perovskite solar cells have revolutionized the fabrication of solution-processable solar cells. The presence of lead in the devices makes this technology less attractive, and alternative metals in perovskites are being researched as suitable alternatives. We demonstrate a new type of tin-based perovskite absorber that incorporates both ethylenediammonium (en) and formamidinium (FA), forming new materials of the type {en}FASnI3. The three-dimensional ASnI3 structure is stable only with methylammonium, FA, and Cs cations, and the bandgap can be tuned with solid solutions, such as ASnI3-x Br x . We show that en can serve as a new A cation capable of achieving marked increases in the bandgap without the need for solid solutions. The en introduces a new bandgap tuning mechanism that arises from massive Schottky style defects. In addition, incorporation of the en cation in the structure markedly increases the air stability and improves the photoelectric properties of the tin-based perovskite absorbers. Our best-performing {en}FASnI3 solar cell has the highest efficiency of 7.14%, which is achieved for a lead-free perovskite cell, and retains 96% of its initial efficiency after aging over 1000 hours with encapsulation. Our results introduce a new approach for improving the performance and stability of tin-based, lead-free perovskite solar cells.

Current status of electron transport layers in perovskite solar cells: materials and properties

Abstract: Methyl ammonium lead halide-based hybrid perovskite solar cells (PSCs) have been intensively studied in recent years because of their high efficiency and low processing costs. Although there are limited constraints for choosing the planar electron transport layer (ETL) or mesoscale electron transporting material (ETM), a great deal of effort is required in designing complex nanostructures which are effective as ETL/ETM to achieve high open circuit voltage (Voc) and high fill factor (FF) in PSCs. In this review, various inorganic and organic ETLs, as well as inorganic ETM systems, used for PSCs are summarized. The transport mechanism of electrons in these different ETL/ETM materials is discussed along with their effect on Voc on the basis of energy band diagrams with respect to the perovskite absorber. The authors also discuss the microstructure/nanostructure aspect of mesoscopic ETMs, doping and surface functionalization, and the influence of these parameters on solar cell behaviour, performance, and hysteresis effects. The authors also discussed the microstructure/nanostructure aspect of ETL on shape of current density vs. voltage (J–V) hysteresis in this review. Technical issues and recent progress of ETL to improve device efficiency and stability in terms of materials, process, and characterization are summarized.

Roadmap and roadblocks for the band gap tunability of metal halide perovskites

Abstract: Solar cells based on metal-halide perovskite semiconductors inspire high hopes for efficient low cost solar cell technology. This material class exhibits a facile tunability of the band gap making them interesting for multi-junction device technology. We here compare and highlight trends in the band gap tunability and device performance metrics in reported metal halide perovskite alloys of a wide compositional range from low band gap compounds, such as FA0.75Cs0.25Sn0.5Pb0.5I3 with an absorption onset of 1.2 eV, to high bandgap compounds, such as CsPbBr3 with an absorption onset close to 2.4 eV. In between, metal halide perovskites can seemingly be seamlessly tuned by compositional engineering. However, mixed bromide–iodide compounds with band gaps above 1.7 eV often exhibit photo-induced phase segregation inducing domains with lower band gaps that emit photons of low energy. This effect also reduces the photoluminescence quantum yield and hence the maximum open circuit voltage achievable in devices. This highlight summarizes general trends for metal halide perovskites with respect to their absorption onset. Furthermore recent progress as well as possible roadblocks for the band gap tunability of metal halide perovskites are highlighted as this is of particular importance for the development of multifunction solar cell technology.

Performance Enhancement of Lead-Free Tin-Based Perovskite Solar Cells with Reducing Atmosphere-Assisted Dispersible Additive

Abstract: Sn-based halide perovskite materials have attracted tremendous attention and have been employed successfully in solar cells. However, their high conductivities resulting from the unstable divalent Sn state in the structure cause poor device performance and poor reproducibility. Herein, we used excess tin iodide (SnI2) in Sn-based halide perovskite solar cells (ASnI3, A = Cs, methylammonium, and formamidinium tin iodide as the representative light absorbers) combined with a reducing atmosphere to stabilize the Sn2+ state. Excess SnI2 can disperse uniformly into the perovskite films and functions as a compensator as well as a suppressor of Sn2+ vacancies, thereby effectively reducing the p-type conductivity. This process significantly improved the solar cell performances of all the ASnI3 materials on mesoporous TiO2. Optimized CsSnI3 devices achieved a maximum power conversion efficiency of 4.81%, which is the highest among all inorganic Pb-free perovskite solar cells to date.

Progress in Theoretical Study of Metal Halide Perovskite Solar Cell Materials

Abstract: Lead halide perovskites have recently emerged as promising absorbers for fabricating low-cost and high-efficiency thin-film solar cells. The record power conversion efficiency of lead halide perovskite-based solar cells has rapidly increased from 3.8% in 2009 to 22.1% in early 2016. Such rapid improvement is attributed to the superior and unique photovoltaic properties of lead halide perovskites, such as the extremely high optical absorption coefficients and super-long photogenerated carrier lifetimes and diffusion lengths that are not seen in any other polycrystalline thin-film solar cell materials. In the past a few years, theoretical approaches have been extensively applied to understand the fundamental mechanisms responsible for the superior photovoltaic properties of lead halide perovskites and have gained significant insights. This review article highlights the important theoretical results reported in literature for the understanding of the unique structural, electronic, optical, and defect properties of lead halide perovskite materials. For comparison, we also review the theoretical results reported in literature for some lead-free perovskites, double perovskites, and nonperovskites.

Ultrafast Electron Dynamics in Solar Energy Conversion

Abstract: Electrons are the workhorses of solar energy conversion. Conversion of the energy of light to electricity in photovoltaics, or to energy-rich molecules (solar fuel) through photocatalytic processes, invariably starts with photoinduced generation of energy-rich electrons. The harvesting of these electrons in practical devices rests on a series of electron transfer processes whose dynamics and efficiencies determine the function of materials and devices. To capture the energy of a photogenerated electron–hole pair in a solar cell material, charges of opposite sign have to be separated against electrostatic attractions, prevented from recombining and being transported through the active material to electrodes where they can be extracted. In photocatalytic solar fuel production, these electron processes are coupled to chemical reactions leading to storage of the energy of light in chemical bonds. With the focus on the ultrafast time scale, we here discuss the light-induced electron processes underlying the fu...

Quantum dot solar cells

Abstract: Quantum dot (QD)-based solar cells have been the subject of over two decades of research with the hopes of increasing their efficiency to surpass single junction solar cells. To date, no single working device has been developed that surpasses the efficiency of a single junction solar cell. Fundamental issues including unrealistic assumptions involved in theoretical work, tendency of stretching observed experimental results, and lack of both process and dimension control at nanoscale exist with QD-based solar cells making them unlikely to play a significant role in the manufacturing of future generations of PV modules. Silicon (Si)-based photovoltaics (PV) manufacturing will continue to provide sustained growth of the PV industry. This paper presents a review of the fundamental problems associated with QD-based solar cells.

Inorganic CsPbI3 Perovskite-Based Solar Cells: A Choice for a Tandem Device

Abstract: Hygroscopicity risk and organic–inorganic hybrid perovskites easy decomposition in solar cells limit their usefulness. Apart from the hybrid organic–inorganic perovskites, inorganic perovskite solar cells display a better stability toward moisture, light soaking, and thermal stressing. However, most inorganic perovskites are inappropriate for single junction or tandem solar cells due to their large bandgaps (>1.8 eV), which eventually results in light absorption loss. Fortunately, cubic CsPbI3 perovskite (having 1.73 eV bandgap) could potentially serve as top cells in tandem devices with silicon solar cells. Poor phase stability of CsPbI3 is considered a major obstacle to design CsPbI3 perovskite solar cells. This review highlights the most recent studies on the progress in CsPbI3-based solar cell device field. Moreover, this review also summarizes certain strategies to improve phase stability, such as size reduction to nanocrystal or external cations/anions doping, with the aim to improve the devices design.

The Potential of Multijunction Perovskite Solar Cells

Abstract: Metal halide perovskite semiconductors offer rapid, low-cost deposition of solar cell active layers with a wide range of band gaps, making them ideal candidates for multijunction solar cells. Here, we combine optical and electrical models using experimental inputs to evaluate the feasible performances of all-perovskite double-junction (2PJ), triple-junction (3PJ), and perovskite–perovskite–silicon triple-junction (2PSJ) solar cells. Using parameters and design constraints from the current state-of-the-art generation of perovskite solar cells, we find that 2PJs can feasibly approach 32% power conversion efficiency, 3PJs can reach 33%, and 2PSJs can surpass 35%. We also outline pathways to improve light harvesting and demonstrate that it is possible to raise the performances to 34%, 37%, and 39% for the three architectures. Additionally, we discuss important future directions of research. Finally, we perform energy yield modeling to demonstrate that the multijunction solar cells should not suffer from reduc...

Beyond 11% Efficient Sulfide Kesterite Cu2ZnxCd1–xSnS4 Solar Cell: Effects of Cadmium Alloying

Abstract: Kesterite Cu2ZnSnS4 (CZTS) thin-film solar cells have drawn worldwide attention because of outstanding performance and earth-abundant constituents. However, problems such as coexistence of complex secondary phases, the band tailing issue, short minority lifetime, bulk defects, and undesirable band alignment at p–n interfaces need to be addressed for further efficiency improvement. In this regard, Cd alloying shows promise for dealing with some of these problems. In this work, a beyond 11% efficient Cd-alloyed CZTS solar cell is achieved, and the effects of Cd-alloying and mechanism underpinning the performance improvement have been investigated. The introduction of Cd can significantly reduce the band tailing issue, which is confirmed by the reduction in the difference between the photoluminescence peak and optical band gap (Eg) as well as decreased Urbach energy. The microstructure, minority lifetime, and electrical properties of CZTS absorber are greatly improved by Cd alloying. Further XPS analyses sho...