awn

The detrimental over-thick Mo(S _x ,Se_1−x )₂ layer can be suppressed via tailoring the preferred orientation of Mo(S _x ,Se_1−x )₂ induced by adding sulfur during selenization, thus significantly reducing the series resistance of the device and enabling a 62% increase in efficiency for the flexible Cu₂ZnSn(S,Se)₄ solar cell to 8.9%.

Flexible Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells have attracted considerable attention due to their potential application in specific areas such as power sources for wearable electronics. However, the over-thick Mo(S _x ,Se_1−x )₂ at the back contact is one of the factors that limit the device performance. Herein, a facile strategy to inhibit the thick Mo(S _x ,Se_1−x )₂ layer by adding a proper proportion of sulfur during selenization is reported. It is found that the thickness of Mo(S _x ,Se_1−x )₂ can be effectively tailored via tuning the proportion of S, enabling a substantial decrease in series resistance. The suppression mechanism is mainly ascribed to the change of orientation of Mo(S _x ,Se_1−x )₂ induced by S, which limits the diffusion of Se to Mo. Accordingly, the total area efficiency of the flexible CZTSSe device improves significantly from 5.5 to 8.9% with the addition of 2% S, followed by a drop with more S. Furthermore, it is demonstrated that this strategy can also be applied to both kesterite and chalcogenide absorbers deposited on rigid Mo substrates to suppress the thick Mo(S _x ,Se_1−x )₂ layer, indicating the universality of this method. Overall, this work provides a general, facile, and effective approach to modify the back contact interface without introducing extra blocking layers.

This Minireview summarizes the recent developments on interfaces in inorganic perovskite solar cells, with special focus on the fundamental understanding of how interfaces influence the performance of devices. Directions for developing highly efficient and stable inorganic perovskite solar cells by interface engineering are also provided.

Abstract

Owing to their superior thermal stability, metal halide inorganic perovskite materials continue to attract interest for photovoltaics applications. The highest reported power conversion efficiency (PCE) for solar cells based on inorganic perovskites is over 20 %. As this PCE corresponds to 73 % of the theoretical limit, there remains more room for further improving the device PCEs than for improving organic–inorganic hybrid perovskite solar cells (PSCs). The main loss is in the photovoltage, which is limited by interfaces in terms of non-radiative recombination caused by traps and energy-level mismatch. Furthermore, inefficient charge extraction at interfacial contacts reduces the photocurrent and fill factor. This Minireview summarizes the recent developments in the fundamental understanding of how the interfaces and interfacial layers influence the performance of solar cells based on inorganic perovskite absorbers. An outlook for the development of highly efficient and stable inorganic PSCs from the interface point of view is also given.

N719 dye molecules effectively link nickel oxide (NiO _x )/perovskite interfaces by facilitating charge transport, concurrently passivating NiO _x and perovskite surface traps, and forming a barrier that prevents undesirable chemical reactions occurring at the interface. The molecule also self-anchors and conformally covers NiO _x films deposited on complex surfaces, enabling fabrication of highly efficient textured monolithic p-i-n perovskite/silicon tandem solar cells.

Abstract

Sputtered nickel oxide (NiO _x ) is an attractive hole-transport layer for efficient, stable, and large-area p-i-n metal-halide perovskite solar cells (PSCs). However, surface traps and undesirable chemical reactions at the NiO _x /perovskite interface are limiting the performance of NiO _x -based PSCs. To address these issues simultaneously, an efficient NiO _x /perovskite interface passivation strategy by using an organometallic dye molecule (N719) is reported. This molecule concurrently passivates NiO _x and perovskite surface traps, and facilitates charge transport. Consequently, the power conversion efficiency (PCE) of single-junction p-i-n PSCs increases from 17.3% to 20.4% (the highest reported value for sputtered-NiO _x based PSCs). Notably, the N719 molecule self-anchors and conformally covers NiO _x films deposited on complex surfaces. This enables highly efficient textured monolithic p-i-n perovskite/silicon tandem solar cells, reaching PCEs up to 26.2% (23.5% without dye passivation) with a high processing yield. The N719 layer also forms a barrier that prevents undesirable chemical reactions at the NiO _x /perovskite interface, significantly improving device stability. These findings provide critical insights for improved passivation of the NiO _x /perovskite interface, and the fabrication of highly efficient, robust, and large-area perovskite-based optoelectronic devices.

The dynamical behaviors of CsPbI₃ perovskite across temperature and structural phase transitions are investigated theoretically. Two iodine-octahedral-tilt modes soften in the Pm3¯m phase; one sub-THz mode maintains very low frequency in the P4/mbm phase arising from the temporal exploration of various structural states, and it has mixed fluctuations of antiphase iodine tiltings and Cs antipolar motions.

Abstract

Lattice dynamics are often regarded as signatures of the underlying crystal structure. Here, a first-principle-based effective Hamiltonian method combined with molecular dynamics simulations is used to study dynamical behaviors of CsPbI₃ perovskite across temperature and structural phase transitions. A single (short-range tilting) parameter in this effective Hamiltonian is varied in order to make the temperature range of the intermediate tetragonal P4/mbm phase, existing in-between the cubic Pm3¯m and orthorhombic Pnma phases, either broader than observed or completely disappearing. Comparing the dynamics of these different cases allows one to conclude that real CsPbI₃ perovskite should have i) two iodine-octahedral-tilt related modes that differ in frequency but both significantly soften as the temperature decreases within the cubic phase toward the Pm3¯m-to-P4/mbm transition; and ii) one mode that maintains a very low frequency (of the order of 1.0 cm⁻¹) in the entire region of P4/mbm stability, as a result of the temporal exploration of various structural states. Such latter sub-THz mode mixes fluctuations of antiphase iodine tiltings and Cs antipolar motions because of a trilinear energetic coupling.

An efficient interface passivation strategy for integrated perovskite/organic solar cells (IPOSCs) based on layered RP perovskite is demonstrated. The polymer PM6 is developed as the passivation layer to reduce the interface defects and suppress the nonradiation recombination in IPOSCs, leading to an improved V _OC from 1.06 to 1.12 V. The optimized IPOSC exhibits a champion efficiency of 19.15%, much higher than the control device (PCE = 16.33%).

Abstract

Integrated perovskite/organic solar cells (IPOSCs) have shown great potential in broadening the light absorption range and improving the photovoltaic performance. However, the severe interface charge recombination and unmatched energy levels between perovskite and organic photoactive layers hinder their performance improvement. Here, an efficient interface passivation strategy for IPOSCs based on a layered Ruddlesden–Popper (RP) perovskite and high photovoltaic performance is successfully demonstrated. It is found that an ultrathin conjugated polymer (PM6) layer could passivate the surface defects of perovskite film, tuning the energy level and suppress the nonradiative recombination loss, leading to efficient interface contact between RP perovskite and organic photoactive layers, boosting the open-circuit voltage from 1.06 to 1.12 V and the efficiency from 17.23% to 19.15%. Importantly, the optimized device shows extended photocurrent response to 930 nm with a peak intensity close to 50% from 800 to 931 nm. The results indicate that interface passivation using a functionalized polymer could be an efficient strategy to improve the photovoltaic performance of integrated devices.

An efficient interface passivation strategy for integrated perovskite/organic solar cells (IPOSCs) based on layered RP perovskite is demonstrated. The polymer PM6 is developed as the passivation layer to reduce the interface defects and suppress the nonradiation recombination in IPOSCs, leading to an improved V _OC from 1.06 to 1.12 V. The optimized IPOSC exhibits a champion efficiency of 19.15%, much higher than the control device (PCE = 16.33%).

Abstract

Integrated perovskite/organic solar cells (IPOSCs) have shown great potential in broadening the light absorption range and improving the photovoltaic performance. However, the severe interface charge recombination and unmatched energy levels between perovskite and organic photoactive layers hinder their performance improvement. Here, an efficient interface passivation strategy for IPOSCs based on a layered Ruddlesden–Popper (RP) perovskite and high photovoltaic performance is successfully demonstrated. It is found that an ultrathin conjugated polymer (PM6) layer could passivate the surface defects of perovskite film, tuning the energy level and suppress the nonradiative recombination loss, leading to efficient interface contact between RP perovskite and organic photoactive layers, boosting the open-circuit voltage from 1.06 to 1.12 V and the efficiency from 17.23% to 19.15%. Importantly, the optimized device shows extended photocurrent response to 930 nm with a peak intensity close to 50% from 800 to 931 nm. The results indicate that interface passivation using a functionalized polymer could be an efficient strategy to improve the photovoltaic performance of integrated devices.

A residual charge testing approach is used to investigate the trapping and detrapping process in the perovskite solar cells based on the active layers with different crystallization and the morphology. The results reveal that the residual charge exists widely at the grain boundary, and the residual charge is related to the performance of the perovskite solar cells.

Abstract

The performance of perovskite solar cells is greatly affected by the crystallization of the perovskite active layer. Perovskite crystal grains should neatly arrange and penetrate the entire active layer for an ideal perovskite crystallization. These kinds of crystallized perovskite films exhibit fewer defects and longer carrier lifetime, which is beneficial to enhance the performance of perovskite solar cells. Here, by testing the residual charge of perovskite solar cells with different crystallization conditions, it is demonstrated that the residual charge exists widely at the grain boundary, which is parallel to the device, and the residual charge is related to the performance of the perovskite solar cells. Single crystal grains neatly arranged and penetrate the entire active layer can generate less residual charge and improve device performance of the perovskite solar cells. The results also show that the long decay time of open-circuit voltage comes from the detrapping of trapped carriers. The residual charge testing technology provides a new idea for the investigation of carrier trap and detrap characteristics in photovoltaic devices.

A novel catalytic heterojunction made of Cs₃Bi₂Br₉ and g-C₃N₄ is reported. The good band alignment between the two semiconductors provides the path to improve the carrier dynamics, and to promote a synergic effect resulting in improved photocatalytic hydrogen evolution and organic dye degradation reactions.

Abstract

The rational design of heterojunctions based on metal halide perovskites (MHPs) is an effective route to create novel photocatalysts to run relevant solar-driven reactions. In this work, an experimental and computational study on the synergic coupling between a lead-free Cs₃Bi₂Br₉ perovskite derivative and g-C₃N₄ is presented. A relevant boost of the hydrogen photogeneration by more than one order of magnitude is recorded when going from pure g-C₃N₄ to the Cs₃Bi₂Br₉/g-C₃N₄ system. Effective catalytic activity is also achieved in the degradation of the organic pollutant with methylene blue as a model molecule. Based upon complementary experimental outputs and advanced computational modeling, a rationale is provided to understand the heterojunction functionality as well as the trend of hydrogen production as a function of perovskite loading. This work adds further solid evidence for the possible application of MHPs in photocatalysis, which is emerging as an extremely appealing and promising field of application of these superior semiconductors.

A series of triplet acceptors are synthesized via regulating the alkyl side chains. The effects of side-chain engineering on the optoelectronic properties, packing behaviors, triplet properties, energy losses, charge transport properties, spin lifetimes of triplet polarons, blend film morphologies, and overall photovoltaic performance are systematically studied. This work enhances the understanding of the structure–property relationship for high-performance triplet acceptors.

Triplet excitons have both longer lifetimes and diffusion lengths than singlet excitons due to the nature of triplet excitons, which is expected to increase the photocurrent and further improve the performance of organic solar cells (OSCs). However, the working mechanism of triplet excitons in OSCs is not clearly clarified. Therefore, it is urgent to develop new triplet acceptors for in-depth understanding. Herein, a series of acceptors (BTn-4Cl) are synthesized by fine-tuning of the side-chain branch positions. The generation of triplet excitons of BTn-4Cl is confirmed by the time-resolved photoluminescence (TRPL) spectra, magnetophotocurrent (MPC) experiment, and electron paramagnetic resonance (EPR) spectra. The effects of side-chain engineering on the optoelectronic properties, packing behaviors, energy losses, charge transport properties, spin lifetimes of triplet polarons, and blend film morphologies are systematically studied. These results show that D18:BT3-4Cl-based OSCs possess the best power conversion efficiency (PCE) of 17.31% due to lower energy losses, less recombination losses, more balanced charge carrier mobilities, longer spin–lattice (T ₁) relaxation time, and more favorable morphology. This work enhances the understanding of the structure–property relationship for high-performance triplet acceptors.

Optimizing perovskite vertical crystallization is achieved by the newly developed buried composite layer by introducing graphitic carbon nitride (g-C₃N₄) into tin oxide, which benefits from the pre-nucleation of lead-rich species induced by the rich amino groups on g-C₃N₄, fulfilling the enhanced efficiencies in solar cells. Our findings provide new insight into vertically manipulating the perovskite films from the buried contact.

Planar-heterojunction perovskite solar cells (PSCs) have experienced rapid evolution in recent years because of the low-temperature processing, suitable alignment, and high mobility of the tin oxide buried contact layer. However, improper SnO₂ surface states and poor crystallinity of the top perovskite films are still the main obstacles for the planar PSCs in which performance always lags behind their mesoporous counterparts. Herein, a new buried contact is reported by introducing graphitic carbon nitride (g-C₃N₄) into the commonly used SnO₂ which performs outstanding transmittance, conductivity, and surface states for a high-quality electron-transporting layer. Moreover, the vertical composition and crystallinity of the top perovskite film are manipulated by rich amino groups on the edge of the g-C₃N₄ nanosheets which induce the prenucleation of the lead-rich species at the buried interface. Benefiting from the high-quality buried contacts and the optimized perovskite layers, the resultant PSCs achieve a champion efficiency of 21.5% with all photovoltaic parameters enhanced in comparison with their control counterparts (<20%).

The nanophotonic perovskite solar cell covered with an array of nanodome or nanohole structures can provide enhanced light incoupling compared with the planar device, resulting in improved J _SC by ∼10–15% and strengthening of the omnidirectional capabilities. Such optimized nanophotonic front contacts can benefit from realizing 30% power conversion efficiency in the case of perovskite/perovskite tandem solar cells.

The front contact of solar cells greatly influences the optoelectronic performance of perovskite solar cells (PSCs) by controlling the coherent light propagation as well as charge transport within the device. Herein, the nanophotonic front contact consisting of multilayer nanodomes and nanoholes for high-efficiency perovskite single-junction and perovskite/perovskite tandem solar cells (PVK/PVK TSCs) is investigated. The optical and electrical characteristics of solar cells are investigated by conducting an advanced 3D numerical approach with the combination of finite-difference time-domain (FDTD) and finite-element method (FEM) simulations embedded with the particle swarm optimization (PSO) algorithm. The numerical modeling is validated by fabricating a set of efficient PSCs, optimized to a power conversion efficiency (PCE) of 17.9%, V _OC of 1.07 V, J _SC of 21.8 mA cm⁻² and fill factor (FF) of 77%. The nanophotonic device results in improved J _SC by 10−15%, resulting from 10−15% enhanced light incoupling compared with the planar device, while also strengthening the omnidirectional capabilities at angles of illumination as high as 40°. The optimized nanophotonic front contact results in PCEs of >23% and >30% (matched J _SC ≈18 mA cm⁻²) for single-junction PSCs and PVK/PVK TSCs, respectively. Details of the nanophotonic front contact, device, and fabrication process are provided.

Genetic modification of M13 bacteriophages amplifies amino acid K, which functions as a perovskite growth template and a stronger passivator than the wild-type virus in PSCs. The modified virus-added PSCs exhibit a higher PCE (23.6%) than wild-type M13 virus-added devices (22.8%). The observed enhancement is attributed to slightly larger perovskite grains, stronger grain boundary passivation, and improved hole conductivity.

Abstract

Perovskite solar cells (PSCs) are considered to be one of the most promising solar energy harvesters owing to their high power conversion efficiency (PCE). To increase their PCE even further, additives are used; however, some of these additives pose certain disadvantages, which limit their applications to PSCs. Therefore, in this study, the nature-inspired ecofriendly M13 bacteriophage is genetically engineered to maximize its performance as a perovskite crystal growth template and as a passivator for PSCs. The genetic manipulation of the M13 bacteriophage enhances the Lewis coordination between the perovskite materials and single-stranded virus by amplifying a designated amino acid group. Among the 20 types of amino acids, lysine (Lys or K), arginine (Arg or R), and methionine (Aug or M) exhibit the strongest interaction with the perovskite materials. Results suggest that the K-amplified genetically engineered M13 bacteriophage is the most effective. The K-type M13 virus-inoculated PSCs yield a PCE of 23.6% in the laboratory. This device, when taken to a national laboratory for verification, exhibits a certified forward and reverse bias-combined efficiency (22.3%), which, to the best of the authors’ knowledge, is one of the highest efficiencies reported among the biomaterial-based PSCs.

Time of flight currents shed light on the interaction of free electrons and holes with defects in MAPbI₃ perovskite. Reconstruction of carrier transport dynamics reveals the effect of defects on diffusion length, lifetime, and mobility. Photo-Hall and thermoelectric spectroscopies assess parameters of defects. Advanced characterization of charge transport and defects can stimulate new device architectures and material modification pathways.

Abstract

The interaction of free carriers with defects and some critical defect properties are still unclear in methylammonium lead halide perovskites (MHPs). Here, a multi-method approach is used to quantify and characterize defects in single crystal MAPbI₃, giving a cross-checked overview of their properties. Time of flight current waveform spectroscopy reveals the interaction of carriers with five shallow and deep defects. Photo-Hall and thermoelectric effect spectroscopy assess the defect density, cross-section, and relative (to the valence band) energy. The detailed reconstruction of free carrier relaxation through Monte Carlo simulation allows for quantifying the lifetime, mobility, and diffusion length of holes and electrons separately. Here, it is demonstrated that the dominant part of defects releases free carriers after trapping; this happens without non-radiative recombination with consequent positive effects on the photoconversion and charge transport properties. On the other hand, shallow traps decrease drift mobility sensibly. The results are the key for the optimization of the charge transport properties and defects in MHP and contribute to the research aiming to improve perovskite stability. This study paves the way for doping and defect control, enhancing the scalability of perovskite devices with large diffusion lengths and lifetimes.

By designing new donor/acceptor materials and combining a ternary blending strategy, a maximum power conversion efficiency (PCE) of 19.0% (certified value of 18.7%) in single-junction organic photovoltaic (OPV) cells is achieved. It is demonstrated that finely tuning the light utilization and photophysical processes of the active layer has great potential for further improving the PCEs of OPV cells.

Abstract

Improving power conversion efficiency (PCE) is important for broadening the applications of organic photovoltaic (OPV) cells. Here, a maximum PCE of 19.0% (certified value of 18.7%) is achieved in single-junction OPV cells by combining material design with a ternary blending strategy. An active layer comprising a new wide-bandgap polymer donor named PBQx-TF and a new low-bandgap non-fullerene acceptor (NFA) named eC9-2Cl is rationally designed. With optimized light utilization, the resulting binary cell exhibits a good PCE of 17.7%. An NFA F-BTA3 is then added to the active layer as a third component to simultaneously improve the photovoltaic parameters. The improved light unitization, cascaded energy level alignment, and enhanced intermolecular packing result in open-circuit voltage of 0.879 V, short-circuit current density of 26.7 mA cm⁻², and fill factor of 0.809. This study demonstrates that further improvement of PCEs of high-performance OPV cells requires fine tuning of the electronic structures and morphologies of the active layers.

Hybrid perovskites are promising absorber materials for photovoltaic applications. In this work, triple-cation perovskite is deposited by sequential slot-die coating. This industrially scalable thin film fabrication process allows for homogeneous perovskite layer deposition on 5 cm × 10 cm substrates. Solar cell devices with up to 19%, and mini-modules with 15.2%, power conversion efficiencies are demonstrated using this method.

Abstract

Development of industrially relevant thin-film deposition processes is a necessity for upscaling the perovskite solar cell technology to commercial product-level. This work reports on a sequential deposition method for state-of-the art triple cation perovskite by slot-die coating. During this two-step process, first, a layer of lead iodide mixed with cesium iodide is deposited, followed by applying the organic cations on top, inducing conversion to perovskite during a second slot-die coating step. By carefully tuning the ink composition and the deposition parameters, uniform perovskite layers of 5 × 10 cm² are obtained. Power conversion efficiencies up to 19% for small laboratory solar cells adopting a planar device configuration and up to 15.2% for mini-modules with an aperture area of 12 cm² are presented. These values are among the highest efficiencies achieved in the literature for slot-die-coated perovskite.

Passivating contacts based on poly-Si have demonstrated excellent passivation capabilities. TOPCon as such a concept is applied on lowly doped wafers that received the best-known pretreatment. The resulting very high minority charge carrier lifetimes are acquired by multiple methods and record lifetimes of 0.18 s on p-type and 0.5 s on n-type crystalline silicon are reported.

Recent progress in surface passivation technology and wafer pretreatment already resulted in significant improvements in the achievable minority charge carrier lifetime of crystalline silicon. Herein, this is further exemplified by studying the lifetime on lowly doped crystalline silicon wafers passivated by poly-Si. To ensure credible lifetime measurements multiple measurement techniques are compared and good agreement between the investigated approaches is found. The resulting lifetime curves are analyzed in detail and the main limitation is very likely caused by silicon bulk recombination—most likely due to impurities. This analysis indicates that even very low impurity concentrations can be a limiting factor at the extraordinary high level of charge carrier lifetime observed in this study. Despite these limitations, lifetimes of 0.18 s on p-type and 0.5 s on n-type crystalline silicon wafers are measured, which to our knowledge exceed previously reported lifetimes. In both cases, these measured lifetimes correspond to an effective minority charge carrier diffusion length of ≈2.5 cm.

A cold-aging induced aggregation approach is demonstrated to enhance device efficiency of organic solar cells via tuning of the pre-aggregates of polymer donor PM6 in solution and therefore in its solid photovoltaic blend films with a range of fused-ring and non-fused-ring non-fullerene electron acceptors.

Abstract

The molecular ordering and pre-aggregation of photovoltaic materials in solution can significantly affect the nanoscale morphology in solid photoactive layers, and play a vital role in determining the power conversion efficiency (PCE) of organic solar cells (OSCs). Herein, a cold-aging strategy is reported to mediate the pre-aggregation of PM6 polymer in solution through a disorder-order transition, which leads to dense and fine PM6 aggregates with enhanced π−π stacking in its blend thin films with either fused-ring and non-fused-ring non-fullerene acceptors (NFAs) including Y6-BO, N3, IT-4F, and PTIC. The fine aggregates of PM6 and slightly enlarged NFA domains improve the continuous networks with enhanced and balanced charge mobility. The resulting OSCs all demonstrate enhanced PCEs compared to their counterparts without any cold-aging treatments, with PM6:Y6-BO OSC being most effective from 16.6% to 17.7%, demonstrating the universality of this approach. This can be further optimized upon casting of the cold-aging solution with the presence of solvent vapor, resulting in a champion PCE of 18.0% for PM6:Y6-BO OSC, which is the highest PCE of this OSC reported in the literature. This work provides a rational guide for optimizing non-fullerene OSCs via aggregation control before and during the solution casting process.

In this study, transient optical spectroscopy methods are used to quantify the temperature dependence of charge generation dynamics in efficient non-fullerene organic photovoltaic blends with a negligible driving force. The results show that the photogenerated electron–hole pairs can thermally separate at the D/A interface, given that they are sufficiently long-lived (even at a reduced temperature for state-of-the-art materials).

Abstract

Transient optical spectroscopy is used to quantify the temperature-dependence of charge separation and recombination dynamics in P3TEA:SF-PDI₂ and PM6:Y6, two non-fullerene organic photovoltaic (OPV) systems with a negligible driving force and high photocurrent quantum yields. By tracking the intensity of the transient electroabsorption response that arises upon interfacial charge separation in P3TEA:SF-PDI₂, a free charge generation rate constant of ≈2.4 × 10¹⁰ s⁻¹ is observed at room temperature, with an average energy of ≈230 meV stored between the interfacial charge pairs. Thermally activated charge separation is also observed in PM6:Y6, and a faster charge separation rate of ≈5.5 × 10¹⁰ s⁻¹ is estimated at room temperature, which is consistent with the higher device efficiency. When both blends are cooled down to cryogenic temperature, the reduced charge separation rate leads to increasing charge recombination either directly at the donor-acceptor interface or via the emissive singlet exciton state. A kinetic model is used to rationalize the results, showing that although photogenerated charges have to overcome a significant Coulomb potential to generate free carriers, OPV blends can achieve high photocurrent generation yields given that the thermal dissociation rate of charges outcompetes the recombination rate.

Publication date: November 2021

Source: Nano Energy, Volume 89, Part B

Author(s): Yingchun Niu, Chen Tian, Jiajia Gao, Fan Fan, Yida Zhang, Yuanyuan Mi, Xiangcheng Ouyang, Lina Li, Jiapeng Li, Siyuan Chen, Yinping Liu, Hong-Liang Lu, Xuelin Zhao, Lifeng Yang, Huanxin Ju, Yingguo Yang, Chuan-Fan Ding, Meng Xu, Quan Xu

Publication date: November 2021

Source: Nano Energy, Volume 89, Part B

Author(s): Jiazheng Zhou, Xiao Xu, Biwen Duan, Huijue Wu, Jiangjian Shi, Yanhong Luo, Dongmei Li, Qingbo Meng

The series resistance is modulated by shortening the charge transport distance in the conductivity-limited electrodes through busbar and device geometry design and preparing a bilayer carbon electrode to improve the performance of large-area-printable mesoscopic perovskite solar cells. Further reducing series resistance is important for the development of efficient large-area perovskite solar modules.

Perovskite solar cells (PSCs) have achieved a certified power conversion efficiency (PCE) of 25.5% and show potential for low-cost photovoltaic applications. One key of pushing PSCs into industrialization is enlarging their areas. However, the PCE of larger-area PSCs is dramatically limited by the undesired increase in series resistance (R _S), which leads to obvious loss of fill factor (FF). Herein, R _S in fully printable mesoscopic PSCs is modulated with a carbon electrode by optimizing the device geometry, preparing busbars to collect currents from electrodes and improving the conductivity of the back electrode. A rectangular device shape and tin busbars on conductive substrate effectively reduce the R _S. Meanwhile, an additional hot-pressed highly conductive low-temperature carbon layer on the back carbon electrode also reduces the R _S. An enhanced PCE of 13.99% for 1 cm² PSCs by R _S modulation is obtained, whereas the control device exhibits a PCE of 7.74%. The PCE increase is due to the improvement of FF from 0.372 to 0.638 with reduced R _S from 27.13 to 9.66 Ω cm².

Unique hetero-structured CsPbI₃/CaF₂ perovskite/fluoride nanocomposites are constructed for fabricating efficient and ultra-stable perovskite solar cells (PSCs). The PSC device based on CsPbI₃/CaF₂-deposited Cs_0.05FA_0.81MA_0.14PbI_2.55Br_0.45 thin-film yields a best power conversion efficiency (PCE) of 21.06% and can retain 85% of its original PCE after 1000 h of continuous operation at the maximum power point tracking under AM 1.5G illumination.

Abstract

Organic-inorganic hybrid perovskite solar cells (PSCs) have rapidly developed over the past decade and have achieved the latest certified power conversion efficiency (PCE) up to 25.5%. However, unsatisfactory long-term operational stability for these hybrid PSCs remains a huge obstacle to further development and commercialization. Herein, a unique hetero-structured CsPbI₃/CaF₂ perovskite/fluoride nanocomposites (PFNCs) is fabricated via a newly developed facile two-step hetero-epitaxial growth strategy to deliver efficient and ultra-stable PSCs. After being incorporated into the crystal lattice of α-phase CsPbI₃ perovskite, the cubic-phase CaF₂ in the resultant CsPbI₃/CaF₂ PFNCs can not only passivate the intrinsic defects of CsPbI₃ perovskite itself but also effectively suppress the notorious ion migration in hybrid perovskite Cs_0.05FA_0.81MA_0.14PbI_2.55Br_0.45 (CsFAMA) thin-films of PSCs. As such, the CsFAMA PSC devices based on CsPbI₃/CaF₂-deposited perovskite thin-film achieve a mean PCE of 20.45%, in sharp contrast to 19.33% of the control devices without deposition. Specifically, the CsPbI₃/CaF₂-deposited PSC retains 85% of its original PCE after 1000 h continuous operation at the maximum power point under AM 1.5G solar light, far better than those of the control and CsPbI₃-deposited PSCs with a device T ₈₅ lifetime of 315 and 125 h, respectively.