Power Conversion Efficiency Loss Research Articles

Stable and Colorful Perovskite Solar Cells Using a Nonperiodic SiO2/TiO2 Multi-Nanolayer Filter.

While research on building-integrated photovoltaics (BIPVs) has mainly focused on power-generating window applications, the utilization of other underutilized surface areas in buildings, including exteriors, facades, and rooftops, has still not been fully explored. The most important requirements for BIPVs are color, power conversion efficiency (PCE), and long-term stability. In this work, we achieved colorful (red, green, blue, RGB) perovskite solar cells (PSCs) with minimized PCE loss (<10%) and enhanced photostability by exploiting the optical properties of nonperiodic multi-nanolayer, narrow-bandwidth reflective filters (NBRFs). The NBRFs were fabricated by multilayering high-index TiO2/low-index SiO2 in a nonperiodic manner, which allowed devices to demonstrate various colors with effectively suppressed unwanted baseline ripple-shape reflectance. The PCEs of PSCs with nonperiodic RGB-NBRFs were 18.0%, 18.6%, and 18.9%, which represent reductions of only 10%, 7%, and 6% of PCE values, respectively, compared to a black control PSC (20.1%). Moreover, the photostability of the PSCs was substantially improved by using the NBRFs because of ultraviolet blocking in the TiO2 layers. The G-PSC retained 65% of the initial PCE after 60 h of continuous illumination (AM 1.5G one sun) at the maximum power point, whereas the black PSC retained only 30%. Aesthetic color value, low PCE loss, and enhanced photostability of PSCs were simultaneously achieved by employing our NBRFs, making this a promising strategy with potential applicability in power-generating building exteriors.

Solution‐Processed 2D Nb2O5(001) Nanosheets for Inverted CsPbI2Br Perovskite Solar Cells: Interfacial and Diffusion Engineering

Herein, solution‐processed 2D Nb2O5(001) nanosheets (c‐Nb2O5 NS) are prepared and combined with [6,6]‐phenyl‐C61‐butyric acid methyl ester (PC61BM) as an electron transport layer (ETL) for inverted inorganic CsPbI2Br perovskite solar cells (PeSCs). The PeSCs with a c‐Nb2O5/PC61BM bilayer ETL yield a high power conversion efficiency (PCE) up to 11.74%, remarkably outperforming the devices with only PC61BM (9.10%) and those with the state‐of‐the‐art ZnO/C60 ETL (10.65%) prepared under the same conditions. More importantly, the nonencapsulated PeSCs with c‐Nb2O5 exhibit a high thermal stability with only 20% PCE loss after 400 h thermal aging at 85 °C. Such an impressive performance and a high stability can be attributed to the introduction of c‐Nb2O5(001) NS with favorable band levels, strong acid nature, and the small lattice fringe spacing along the large lateral (001) surface, which not only facilitate the electron transport, blocking the hole transport, but also contribute to defect passivation and retard the iodine ions diffusion toward the Ag electrode. This study thus provides a deeper insight for the interfacial design in inverted inorganic PeSCs and contributes to PCE improvement in the future.

Elevated Stability and Efficiency of Solar Cells via Ordered Alloy Co-Acceptors

Power conversion efficiency (PCE) and long-term stability are the two key parameters of photovoltaic devices to meet standards for commercial use. In this Letter, an ordered alloyed co-acceptor by incorporating PC61BM and COi8DFIC is obtained. This ordered alloy structure increases the light absorption by producing a shoulder peak at 935 nm and improves electron mobility from 1.51 × 10–5 to 8.91 × 10–4 cm2 V–1 s–1 by PC61BM interacting with the end group of COi8DFIC and connecting adjacent COi8DFIC molecules. Consequently, the PCE is enhanced from 10.80 to 14.22%, enhancement of about 32%. Even further, the device stability is improved due to the fact that the alloy fixes the morphology of the active layer. After keeping for 7200 h, about 10 months, the PCE of those solar cells is retained at 13.2%, corresponding to a PCE loss of only 5.7%, while the PCE loss in the binary control device is up to 33.3%.

Controllable Perovskite Crystallization via Antisolvent Technique Using Chloride Additives for Highly Efficient Planar Perovskite Solar Cells

AbstractThe presence of surface and grain boundary defects in organic–inorganic halide perovskite films can be detrimental to both the performance and operational stability of perovskite solar cells (PSCs). Here, the effect of chloride additives is studied on the bulk and surface defects of the mixed cation and halide PSCs. It is found that using an antisolvent technique, the perovskite film is divided into two layers, i.e., a bottom layer with large grains and a thin capping layer with small grains. The addition of formamidinium chloride (FACl) into the precursor solution removes the small‐grained perovskite capping layer and suppresses the formation of bulk and surface defects, providing a perovskite film with enhanced crystallinity and large grain size of over 1 µm. Time‐resolved photoluminescence measurements show longer lifetimes for perovskite films modified by FACl and subsequently passivated by 1‐adamantylamine hydrochloride as compared to the reference sample. Impedance spectroscopy measurements show that these treatments reduce the recombination in the PSCs, leading to a champion device with power conversion efficiency (PCE) of 21.2%, an open circuit voltage of 1152 mV and negligible hysteresis. The Cl treated PSC also shows improved operational stability with only 12% PCE loss after 700 h under continuous illumination.

Real reason for high ideality factor in organic solar cells: Energy disorder

Organic semiconductor has recently emerged as a promising and versatile material for solar cells. This paper shows that the structural order of the electron transport layers has a significant influence on the ideality factor and the power conversion efficiency of organic solar cells. By using Fermi-Dirac distribution, we demonstrate that both ideality factor and degeneracy will up to 3, even 6, when the energy disorder of the transport layer is large enough. By comparing the numerical values of 15 materials with experimental data, our results show that the ideality factor is almost the same value as the degeneracy when the light intensity gets near to 1 mW/cm2. Additionally, both degeneracy and ideality factor have a positive correlation with the energy disorder. However, the power conversion efficiency will decrease as the energy disorder increasing. These results shed light on the real reason for high ideality factor and the origin of the power conversion efficiency loss, and provide a direction to increase the power conversion efficiency of the organic solar cells.

Control of Crystal Growth toward Scalable Fabrication of Perovskite Solar Cells

AbstractWith the impressive record power conversion efficiency (PCE) of perovskite solar cells exceeding 23%, research focus now shifts onto issues closely related to commercialization. One of the critical hurdles is to minimize the cell‐to‐module PCE loss while the device is being developed on a large scale. Since a solution‐based spin‐coating process is limited to scalability, establishment of a scalable deposition process of perovskite layers is a prerequisite for large‐area perovskite solar modules. Herein, this paper reports on the recent progress of large‐area perovskite solar cells. A deeper understanding of the crystallization of perovskite films is indeed essential for large‐area perovskite film formation. Various large‐area coating methods are proposed including blade, slot‐die, evaporation, and post‐treatment, where blade‐coating and gas post‐treatment have so far demonstrated better PCEs for an area larger than 10 cm2. However, PCE loss rate is estimated to be 1.4 × 10−2% cm−2, which is 82 and 3.5 times higher than crystalline Si (1.7 × 10−4% cm−2) and thin film technologies (≈4 × 10−3% cm−2) respectively. Therefore, minimizing PCE loss upon scaling‐up is expected to lead to PCE over 20% in case of cell efficiency of &gt;23%.

Copper Incorporation in Organic‐Inorganic Hybrid Halide Perovskite Solar Cells

AbstractThe organic‐inorganic hybrid halide perovskite solar cell with excellent photovoltaic performance has been considered a promising device in photovoltaic field. By element substitution in perovskites, the crystal structure and properties of materials can be altered. Herein, two copper‐based compounds are used as additives in perovskites, which affect the crystallization process of perovskite films, and modify the photoelectric properties of perovskite materials. It is found that an appropriate addition of copper (Cu) ions could not only reduce the perovskite phase transition temperature, promote the formation of black perovskite phase, but also improve the crystallization and absorbance of perovskites. Excessive Cu incorporation leads to significant loss of device performance. The appropriate concentration of Cu ions in perovskite absorber for high efficiency solar cell is considered to be ∼0.1 mol% from a number of experimental results, which contributes to a remarkable stability of the device with only 2% power conversion efficiency loss after 170 h. This study is conducive to the comprehensive understanding of the effect of ions doping in perovskite materials.

Avoidance of boron rich layer formation in the industrial boron spin-on dopant diffused n-type silicon solar cell without additional oxidation process

In the present work, the properties of boron rich layer (BRL) formed in the boron spin-on dopant diffusion as well as the avoidance of BRL formation without additional oxidation process are studied. The boron concentration distributions characterized by SIMS exhibit the formation and avoidance of BRL with the variation of oxygen content in the boron diffusion process. The existence of BRL can degrade the minority carrier lifetime due to the enhancement of recombination as well as weaken the anti-reflection effect due to the unmatched refractive index of BRL and SiO2/SiNx stack layers. The decreased minority carrier lifetime together with the increased surface reflectance eventually deteriorates the electrical behavior of solar cell with a maximum power conversion efficiency loss of 0.55%. Significantly, the formation of BRL is found to be avoided due to the complete oxidation of excess elemental boron atoms when the oxygen content increases to 10%, contributing to the recovery of solar cells’ electrical performance with an average efficiency of 19.47%. The present work will be helpful to deepen the understanding of BRL and simplify the boron diffusion process for massive cell production.

Interface Engineering in n‐i‐p Metal Halide Perovskite Solar Cells

Recent years have witnessed continuous progress in metal halide perovskite (MHP) solar cells with a certified power conversion efficiency (PCE) exceeding 22%. However, the commercialization of MHP solar cells continues to encounter various challenges including stabilization, scalability and repeatability. Of all problems related to MHP materials, interface recombination is the most prominent, resulting in severe PCE loss within a short time. Fortunately, interface engineering has been identified as an efficient means of achieving better energy‐level alignment, reduced charge recombination, trap passivation, elimination of photocurrent hysteresis, and enhanced long‐term device stability. This review examines the relationship between specific interface modification layers and their roles in interface engineering based on device physics, revealed by several characterization methods. The latest research advances in interface modification layers according to their roles and properties are also summarized.

Enhanced stability and efficiency of Sn containing perovskite solar cell with SnCl2 and SnI2 precursors

Presence of toxic Pb and device stability are the main issues with perovskite solar cell. For Pb replacement, most likely substitute is Sn, which is a metal of group 14 (like Pb). Thus, in the present study, the amount of Pb is reduced and replaced by Sn. To achieve the replacement, use of SnCl2 is explored in addition to generally used precursor (SnI2), as the source of Sn. Molar ratio of PbI2:SnCl2/SnI2 is varied to get optimum performance of perovskite solar cell. Pt–FTO counter electrode is used in addition to spiro-MeTAD (as hole transport material). The power conversion efficiency of solar cells containing 2:2 molar ratio of PbI2:SnCl2 was enhanced to 10.10%, and PbI2:/SnI2 was enhanced to 10.61%. Without Sn addition (CH3NH3PbI3) the efficiency was only 7.39%. The clear enhancement of 37% (SnCl2) and 43% (SnI2) is highly encouraging, as it leads to less toxic and highly efficient solar cells at the same time. In addition, the percentage loss in power conversion efficiency of device prepared with SnCl2 (CH3NH3Pb0.5Sn0.5ICl2) was also superior (10 days).

Influence of Hot Spot Heating on Stability of Large Size Perovskite Solar Module with a Power Conversion Efficiency of ∼14%

Making perovskite solar cell technology commercially viable is facing a challenge that scaling-up of a small device always experiences a substantial reduction in power conversion efficiency (PCE). In this research, we adopted a volume expansion routine to scale-up from a 0.16 cm2 laboratory-scale device to large size perovskite solar module (PSM) with a PCE loss of 8% and reached a certified PCE of 13.98%. The PCE of the PSM with Au electrode dropped about 40% of the initial efficiency after 16 days’ storage, while the efficiency of PSM with Cu as counter electrode retained 90% of the initial after 30 days’ storage. We also introduced hot spots heating (HSH) characterization method to investigate the stability of PSM. HSH reveals that Cu electrode greatly reduces numbers of hot spots and extent of temperature increase in a PSM compared with Au electrode. Therefore, counter electrode also plays an important role in the stability improvement of PSM.

Interface Engineering for All-Inorganic CsPbI2 Br Perovskite Solar Cells with Efficiency over 14.

In this work, a SnO2 /ZnO bilayered electron transporting layer (ETL) aimed to achieve low energy loss and large open-circuit voltage (Voc ) for high-efficiency all-inorganic CsPbI2 Br perovskite solar cells (PVSCs) is introduced. The high-quality CsPbI2 Br film with regular crystal grains and full coverage can be realized on the SnO2 /ZnO surface. The higher-lying conduction band minimum of ZnO facilitates desirable cascade energy level alignment between the perovskite and SnO2 /ZnO bilayered ETL with superior electron extraction capability, resulting in a suppressed interfacial trap-assisted recombination with lower charge recombination rate and greater charge extraction efficiency. The as-optimized all-inorganic PVSC delivers a high Voc of 1.23 V and power conversion efficiency (PCE) of 14.6%, which is one of the best efficiencies reported for the Cs-based all-inorganic PVSCs to date. More importantly, decent thermal stability with only 20% PCE loss is demonstrated for the SnO2 /ZnO-based CsPbI2 Br PVSCs after being heated at 85 °C for 300 h. These findings provide important interface design insights that will be crucial to further improve the efficiency of all-inorganic PVSCs in the future.

Surface Engineering of TiO2 ETL for Highly Efficient and Hysteresis‐Less Planar Perovskite Solar Cell (21.4%) with Enhanced Open‐Circuit Voltage and Stability

AbstractInterfacial studies and band alignment engineering on the electron transport layer (ETL) play a key role for fabrication of high‐performance perovskite solar cells (PSCs). Here, an amorphous layer of SnO2 (a‐SnO2) between the TiO2 ETL and the perovskite absorber is inserted and the charge transport properties of the device are studied. The double‐layer structure of TiO2 compact layer (c‐TiO2) and a‐SnO2 ETL leads to modification of interface energetics, resulting in improved charge collection and decreased carrier recombination in PSCs. The optimized device based on a‐SnO2/c‐TiO2 ETL shows a maximum power conversion efficiency (PCE) of 21.4% as compared to 19.33% for c‐TiO2 based device. Moreover, the modified device demonstrates a maximum open‐circuit voltage (Voc) of 1.223 V with 387 mV loss in potential, which is among the highest reported value for PSCs with negligible hysteresis. The stability results show that the device on c‐TiO2/a‐SnO2 retains about 91% of its initial PCE value after 500 h light illumination, which is higher than pure c‐TiO2 (67%) based devices. Interestingly, using a‐SnO2/c‐TiO2 ETL the PCE loss was only 10% of initial value under continuous UV light illumination after 30 h, which is higher than that of c‐TiO2 based device (28% PCE loss).

Efficient and Stable Perovskite Solar Cells via Dual Functionalization of Dopamine Semiquinone Radical with Improved Trap Passivation Capabilities

AbstractHighly efficient planar heterojunction perovskite solar cells (PVSCs) with dopamine (DA) semiquinone radical modified poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) (DA‐PEDOT:PSS) as a hole transporting layer (HTL) were fabricated. A combination of characterization techniques were employed to investigate the effects of DA doping on the electron donating capability of DA‐PEDOT:PSS, perovskite film quality and charge recombination kinetics in the solar cells. Our study shows that DA doping endows the DA‐PEDOT:PSS‐modified PVSCs with a higher radical content and greater perovskite to HTL charge extraction capability. In addition, the DA doping also improves work function of the HTL, increases perovskite film crystallinity, and the amino and hydroxyl groups in DA can interact with the undercoordinated Pb atoms on the perovskite crystal, reducing charge‐recombination rate and increasing charge‐extraction efficiency. Therefore, the DA‐PEDOT:PSS‐modified solar cells outperform those based on PEDOT:PSS, increasing open‐circuit voltage (V oc) and power conversion efficiency (PCE) to 1.08 V and 18.5%, respectively. Even more importantly, the efficiency of the unencapsulated DA‐PEDOT:PSS‐based PVSCs are well retained with only 20% PCE loss after exposure to air for 250 hours. These in‐depth insights into structure and performance provide clear and novel guidelines for the design of effective HTLs to facilitate the practical application of inverted planar heterojunction PVSCs.

All-Inorganic CsPbI2Br Perovskite Solar Cells with High Efficiency Exceeding 13.

All-inorganic perovskite solar cells provide a promising solution to tackle the thermal instability problem of organic-inorganic perovskite solar cells (PSCs). Herein, we designed an all-inorganic perovskite solar cell with novel structure (FTO/NiO x/CsPbI2Br/ZnO@C60/Ag), in which ZnO@C60 bilayer was utilized as the electron-transporting layers that demonstrated high carrier extraction efficiency and low leakage loss. Consequently, the as-fabricated all-inorganic CsPbI2Br perovskite solar cell yielded a power conversion efficiency (PCE) as high as 13.3% with a Voc of 1.14 V, Jsc of 15.2 mA·cm-2, and FF of 0.77. The corresponding stabilized power output (SPO) of the device was demonstrated to be ∼12% and remarkably stable within 1000 s. Importantly, the obtained all-inorganic PSCs without encapsulation exhibited only 20% PCE loss with thermal treatment at 85 °C for 360 h, which largely outperformed the organic-species-containing PSCs. The present study demonstrates potential in overcoming the intractable issue concerning the thermal instability of perovskite solar cells.

Influence of binary solvent system on the stability and efficiency of liquid dye sensitized solar cells

Herein we report the stability of liquid-state dye sensitized solar cell (DSSC) with binary solvent system in electrolyte, targeting to combine the advantages of both solvents for the development of highly stable DSSC device without significant loss of device performance. The binary solvent system was prepared from a mixture of acetonitrile and ionic liquid (IL) 1-butyl-3-methylimidazolium bromide with various IL volume ratios. The current-voltage characteristics of the resulting devices revealed variation of the power conversion efficiency (PCE) with the proportion of IL in the electrolytes. Short current density and conversion efficiency dropped while voltage and fill factor generally increased as the amount of ionic liquid increased. The variation pattern in terms of photovoltaic characteristics and charge transfer impedances is consistent with the changes of IL ratio in all devices. The devices were also inspected for more than 46 days/1100 h in open air at room temperature. Those devices containing ionic liquid demonstrated excellent stabilities compared to devices with pure acetonitrile without considerable loss of PCE. Especially those devices with more than 30% ionic liquid retained over 85% efficiency after 46 days, suggesting a promising prospect for commercialization of DSSCs.

Amine treatment induced perovskite nanowire network in perovskite solar cells: efficient surface passivation and carrier transport

In the fabrication of high efficiency organic–inorganic metal halide perovskite solar cells (PSCs), an additional interface modifier is usually applied for enhancing the interface passivation and carrier transport. In this paper, we develop an innovative method with in-situ growth of one-dimensional perovskite nanowire (1D PNW) network triggered by Lewis amine over the perovskite films. To our knowledge, this is the first time to fabricate PSCs with shape-controlled perovskite surface morphology, which improved power conversion efficiency (PCE) from 14.32% to 16.66% with negligible hysteresis. The amine molecule can passivate the trap states on the polycrystalline perovskite surface to reduce trap-state density. Meanwhile, as a fast channel, the 1D PNWs would promote carrier transport from the bulk perovskite film to the electron transport layer. The PSCs with 1D PNW modification not only exhibit excellent photovoltaic performances, but also show good stability with only 4% PCE loss within 30 days in the ambient air without encapsulation. Our results strongly suggest that in-situ grown 1D PNW network provides a feasible and effective strategy for nanostructured optoelectronic devices such as PSCs to achieve superior performances.

Flexible Semiconductor Technologies with Nanoholes-Provided High Areal Coverages and Their Application in Plasmonic-Enhanced Thin Film Photovoltaics

Mechanical flexibility and advanced light management have gained great attentions in designing high performance, flexible thin film photovoltaics for the realization of building-integrated optoelectronic devices and portable energy sources. This study develops a soft thermal nanoimprint process for fabricating nanostructure decorated substrates integrated with amorphous silicon solar cells. Amorphous silicon (a-Si:H) solar cells have been constructed on nanoholes array textured polyimide (PI) substrates. It has been demonstrated that the nanostructures not only are beneficial to the mechanical flexibility improvement but also contribute to sunlight harvesting enhancement. The a-Si:H solar cells constructed on such nanopatterned substrates possess broadband-enhanced light absorption, high quantum efficiency and desirable power conversion efficiency (PCE) and still experience minimal PCE loss even bending around 180°. The PCE performance without antireflection coatings increases to 7.70% and it improves 40% compared with the planar devices. Although the advantages and feasibility of the schemes are demonstrated only in the application of a-Si:H solar cells, the ideas are able to extend to applications of other thin film photovoltaics and semiconductor devices.

Enhanced photovoltaic performance and stability in mixed-cation perovskite solar cells via compositional modulation

Preparation of high-quality and pure phase mixed-organic-cation FA1-xMAxPbI3 perovskite film is a big challenge, especially on a porous oxide scaffold for mesoscopic perovskite solar cells. In this study, we fabricated a pure phase of mixed-organic-cation perovskite FA1-xMAxPbI3 simply using a conventional two-step method. Effect of chemical composition and morphology on the photovoltaic performance and stability of the mixed-organic-cation perovskite has been studied in details. Results show that the FA1-xMAxPbI3 perovskite thin films with a FA+:MA+ molar ratio of 0.7:0.3 demonstrate the best photovoltaic performance. Mesoscopic perovskite solar cells fabricated using these FA0.7MA0.3PbI3 thin films yield a power conversion efficiency (PCE) up to 16.0%. Moreover, the devices present a superior stability and the unsealed devices exposed in ambient condition (25°C, 50%–60% relative humidity) can maintain their photoelectric performance without apparent PCE loss for up to 20 days.

Magnetic field enhancement of organic photovoltaic cells performance

Charge separation is a critical process for achieving high efficiencies in organic photovoltaic cells. The initial tightly bound excitonic electron-hole pair has to dissociate fast enough in order to avoid photocurrent generation and thus power conversion efficiency loss via geminate recombination. Such process takes place assisted by transitional states that lie between the initial exciton and the free charge state. Due to spin conservation rules these intermediate charge transfer states typically have singlet character. Here we propose a donor-acceptor model for a generic organic photovoltaic cell in which the process of charge separation is modulated by a magnetic field which tunes the energy levels. The impact of a magnetic field is to intensify the generation of charge transfer states with triplet character via inter-system crossing. As the ground state of the system has singlet character, triplet states are recombination-protected, thus leading to a higher probability of successful charge separation. Using the open quantum systems formalism we demonstrate that the population of triplet charge transfer states grows in the presence of a magnetic field, and discuss the impact on carrier population and hence photocurrent, highlighting its potential as a tool for research on charge transfer kinetics in this complex systems.