Solution-processed Solar Cells Research Articles

Enhanced Homogeneity in Perovskite Photovoltaic Films via Antisolvent Extraction of a Methylamine-Based Gel Precursor.

Solution-processed perovskite solar cells (PSCs) are at the forefront of next-generation photovoltaics, exhibiting outstanding photoelectric performance and cost-effective manufacturing. However, the prevalent use of polar aprotic solvents such as N,N-dimethylformamide and dimethyl sulfoxide in the preparation of perovskite precursor solution hinders complete solvent removal during film formation. Their high boiling points and strong coordinating abilities lead to solvated intermediates and heterogeneous perovskite crystal nucleation, particularly in the absence of the antisolvent-assisted crystallization. To address this, we developed a methylamine (MA)-based gel dispersion system that significantly improves the uniformity of perovskite films. By employing ethyl acetate (EA) antisolvent extraction, the gel precursor is extracted from a solution of MAI and PbI2 in MA ethanol, which is then diluted in pure acetonitrile (ACN) solvent to form a clear perovskite precursor solution. Benefiting from the highly volatile nature of the ACN-based gel perovskite precursor solution and its rich concentration of high-valent PbIn2-n coordination compounds, this approach enables the fabrication of high-quality MAPbI3 perovskite films, yielding PCEs of 21.34% for PSC and 19.77% for a 5 × 5 cm2 mini-module. This MA-based gel perovskite precursor strategy offers a promising avenue for potential applications in the scalable manufacture of PSCs.

Cu gradient design to attain high efficient solution-processed CuIn(S,Se)2 solar cells

Solution-processed chalcopyrite solar cells are widely regarded as a promising alternative method in reducing the cost compared with vacuum-based techniques. It is noted that the absorber layer usually needs to be prepared under a high insert pressure (∼1.6 atm) to suppress element loss or under a mild pressure but additional surface etching is needed for fabricating high efficient solar cell. Herein, a copper gradient structured precursor is proposed to prepare CuIn(S,Se)2 (CISSe) film under a mild pressure (1.1 atm). The designed gradient Cu not only promotes crystal grain growth and tailors the defects, but also avoids the surface etching of the formed CISSe film for the fabrication of high efficient solar cells. Further, Cu gradient design decreases the conduction band offset of heterojunction, boosting the carriers transport across the p-n heterojunction. Accordingly, a 13.35% efficient CISSe solar cell, comparable to the high efficient CISSe solar cell prepared by this method under high pressure or with film surface etching, is fabricated. This work provides a facile pathway to fabricate high efficient solution-processed chalcopyrite solar cell, avoiding high selenization pressure and film etching, and shows huge potential for solution-processed copper-based solar cells.

Performance investigation of solution-processed semi-transparent perovskite solar cells in building sectors

Semi-transparent perovskite solar cell (PSC) windows have received much attention from scholars due to their remarkable power generation capacity and thermal insulation performance. However, considering the complexity of their fabrication process, and the significant decrease in power generation efficiency when scaling up to large-sized solar modules. To solve the above problems, this study developed a scalable production technological process to prepare translucent PSC modules, in which large-area chalcogenide thin films were prepared by a scratch-coating method. The prepared PSC module has an average visible light transmittance of 20.1 % and shows a maximum power conversion efficiency of 3.92 %. Experimental tests were conducted to investigate its photo-thermal regulation performance concerning the existing common window. The results show that the newly developed photovoltaic window reduces the indoor air temperature by 1.4 °C while the illuminance is reduced by about 59.2 % compared to the common window. A further simulation is performed by Energyplus, with a conclusion that PSC windows can decrease glare probability by 24.7 %–45.7 %, diminish building energy usage by 26.6 %–59.6 %, and achieve up to 469.9 kWh power generation in Harbin, China. The investigation of this paper paves the technical and foundational way for the large-scale application of PSC in building sectors.

16.48% Efficient solution-processed CIGS solar cells with crystal growth and defects engineering enabled by Ag doping strategy

Solution-processed Cu(In,Ga)Se2 (CIGS) solar cells suffer from serious carrier recombination and power conversion efficiency (PCE) loss because of the poor film properties and easy formation of defects. Herein, we propose Ag&Se co-selenization strategy to enhance the crystallization and passivate harmful defects of the CIGS films. The formation of Ag-Se phase during the selenization process enables the formation of large grains and suppresses the deep level defects. It is found that Ag doping can enlarge the depletion region width, lower the Urbach energy and prolong the carrier lifetime. As a result, a champion solution-processed CIGS solar cell presents a high efficiency of 16.48% with the highly improved open-circuit voltage (VOC) of 662 mV and fill factor (FF) of 75.8%. This work provides an efficient strategy to prepare high quality solution-processed CIGS films for high-performance CIGS solar cells.

(Invited) Two-Dimensional Organic-Perovskite Hybrid Materials and Heterostructures

Epitaxial heterostructures based on oxide perovskites and III–V, II–VI and transition metal dichalcogenide semiconductors form the foundation of modern electronics and optoelectronics. Halide perovskites—an emerging family of tunable semiconductors with desirable properties—are attractive for applications such as solution-processed solar cells, light-emitting diodes, detectors and lasers. Their inherently soft crystal lattice allows greater tolerance to lattice mismatch, making them promising for heterostructure formation and semiconductor integration. Atomically sharp epitaxial interfaces are necessary to improve performance and for device miniaturization. However, epitaxial growth of atomically sharp heterostructures of halide perovskites has not yet been achieved, owing to their high intrinsic ion mobility and their poor chemical stability. Therefore, understanding the origins of this instability and identifying effective approaches to suppress ion diffusion are of great importance. In this talk I will present an effective strategy to substantially inhibit in-plane ion diffusion in two-dimensional halide perovskites by incorporating rigid π-conjugated organic ligands. Highly stable and tunable lateral and vertical epitaxial heterostructures, multiheterostructures and superlattices will be demonstrated. Furthermore, using these 2D heterostructures as a new platform, I will present our recent efforts in 1) quantitatively understanding the anion inter-diffusions and migrations, and 2) controlling and manipulating exciton transport and light-emission in halide perovskites.

Nitrogen-rich carbon dots as the antisolvent additive for perovskite-based photovoltaic devices

Solution-processed perovskite solar cells (PSCs) have demonstrated a tremendous growth in power conversion efficiency (PCE). A high-quality, defect-free perovskite-based active layer is a key point to enhance PSC performance. Introduction of additives and interlayers have proved to be an effective tool to passivate surface defects, control crystal growth, and improve PSC stability. Antisolvent engineering has emerged recently as a new approach, which aims to adjust perovskite layer properties and enhance the PCE and stability of PSC devices. Here, we demonstrate that carbon dots (CDs) may serve as a prospective additive for antisolvent engineering. Nitrogen-rich amphiphilic CDs were synthesized from amines by a solvothermal method and used as an additive to chlorobenzene for a perovskite layer fabrication. The interaction between perovskite and functional groups in CDs promotes improved crystallization of an active perovskite layer and defects passivation, bringing higher PSCs efficiency, stability, and suppressed hysteresis. Under optimized CD concentration, the maximum PCE increased by 34% due to the improved short-circuit current and fill factor, and the device maintains 87% of its initial efficiency after 6 d of storage under ambient conditions.

Two-step preparation of methylammonium lead triiodide perovskite film via electrospray deposition of methylammonium iodide solution for solar cell applications

Solution-processable perovskite solar cells (PSCs) have the potential to revolutionize solar cell technology by enabling low power generation costs via low-cost device fabrication. However, most existing research regarding PSCs relies on the spin-coating method, which is not conducive to large-area film deposition. Therefore, the development of an alternative deposition method for perovskite films has become increasingly important for commercialization, for which electrospray deposition is a promising technique. This study investigates the two-step preparation of methylammonium lead triiodide (MAPbI3) perovskite films via the electrospray deposition of a methylammonium iodide (MAI) solution on a spin-coated PbI2 film. The gradual conversion of PbI2 to MAPbI3 with increasing MAI deposition time was revealed, accompanied by an increase in the size of the perovskite crystals. In addition, PSCs were successfully fabricated by electrospraying MAI, achieving a considerable power conversion efficiency of 7.86 % at the optimal MAI deposition time.

Air-Processed All-Inorganic Halide Perovskites Integrated Photorechargeable Supercapacitors.

Due to their easy integration for self-powered operation, integrated energy harvesting and storage could be the game changer in smart, flexible, and portable electronic devices. Three-electrode integration is the most promising approach among all possible configurations because it is less complex and compatible with most techniques. Although the photoconversion efficiency has increased above 20% due to the integration of high-performance perovskite solar cells, the electrochemical storage efficiency (efficacy of the integration) is much below 80% due to a significant potential drop and impedance mismatch. In this context, we introduced perovskite-based solid-state thin film supercapacitors integrated with stable, air-processed perovskite solar cells for an uninterrupted power supply. Our measurement shows that the best performance can be achieved by optimizing several parameters, including series-connected solar cells, light intensity, and photovoltaic active area. The critical challenge with these integrated systems is to maintain a uniform charging current of the supercapacitors throughout the charging cycle while minimizing self-discharging. We achieved an electrochemical storage efficiency of ∼87% at an overpotential of 0.8 V. The overpotential can be as low as 2 mV. We fabricated fully solution-processed series-connected solar cells to integrate with stacked supercapacitors to improve the operating voltage beyond 2.1 V. The photocharging and dark discharging of these integrated devices have been tested over 200 cycles, and a negligible drop in efficiency has been observed. Our detailed energy conversion and storage analysis in these systems unveils the mechanism and losses due to three-terminal integration.

Toward Self-Driven Autonomous Material and Device Acceleration Platforms (AMADAP) for Emerging Photovoltaics Technologies.

ConspectusIn the ever-increasing renewable-energy demand scenario, developing new photovoltaic technologies is important, even in the presence of established terawatt-scale silicon technology. Emerging photovoltaic technologies play a crucial role in diversifying material flows while expanding the photovoltaic product portfolio, thus enhancing security and competitiveness within the solar industry. They also serve as a valuable backup for silicon photovoltaic, providing resilience to the overall energy infrastructure. However, the development of functional solar materials poses intricate multiobjective optimization challenges in a large multidimensional composition and parameter space, in some cases with millions of potential candidates to be explored. Solving it necessitates reproducible, user-independent laboratory work and intelligent preselection of innovative experimental methods.Materials acceleration platforms (MAPs) seamlessly integrate robotic materials synthesis and characterization with AI-driven data analysis and experimental design, positioning them as enabling technologies for the discovery and exploration of new materials. They are proposed to revolutionize materials development away from the Edisonian trial-and-error approaches to ultrashort cycles of experiments with exceptional precision, generating a reliable and highly qualitative data situation that allows training machine learning algorithms with predictive power. MAPs are designed to assist the researcher in multidimensional aspects of materials discovery, such as material synthesis, precursor preparation, sample processing and characterization, and data analysis, and are drawing escalating attention in the field of energy materials. Device acceleration platforms (DAPs), however, are designed to optimize functional films and layer stacks. Unlike MAPs, which focus on material discovery, a central aspect of DAPs is the identification and refinement of ideal processing conditions for a predetermined set of materials. Such platforms prove especially invaluable when dealing with "disordered semiconductors," which depend heavily on the processing parameters that ultimately define the functional properties and functionality of thin film layers. By facilitating the fine-tuning of processing conditions, DAPs contribute significantly to the advancement and optimization of disordered semiconductor devices, such as emerging photovoltaics.In this Account, we review the recent advancements made by our group in automated and autonomous laboratories for advanced material discovery and device optimization with a strong focus on emerging photovoltaics, such as solution-processing perovskite solar cells and organic photovoltaics. We first introduce two MAPs and two DAPs developed in-house: a microwave-assisted high-throughput synthesis platform for the discovery of organic interface materials, a multipurpose robot-based pipetting platform for the synthesis of new semiconductors and the characterization of thin film semiconductor composites, the SPINBOT system, which is a spin-coating DAP with the potential to optimize complex device architectures, and finally, AMANDA, a fully integrated and autonomously operating DAP. Notably, we underscore the utilization of a robot-based high-throughput experimentation technique to address the common optimization challenges encountered in extensive multidimensional composition and parameter spaces pertaining to organic and perovskite photovoltaics materials. Finally, we briefly propose a holistic concept and technology, a self-driven autonomous material and device acceleration platform (AMADAP) laboratory, for autonomous functional solar materials discovery and development. We hope to discover how AMADAP can be further strengthened and universalized with advancing development of hardware and software infrastructures in the future.

Performance and reproducibility analysis of zinc sulfo-selenide and cuprous oxide based perovskite solar cell: A SCAPS study

The combination of titanium dioxide (TiO2) as electron transport layer (ETL) and 2,2’,7,7’-Tetrakis [N,N-di(4-methoxyphenyl)amino]−9,9’-spirobifluorene (Spiro-OMeTAD) as hole transport layer (HTL) have been frequently used in solution-processed perovskite solar cells (PSCs). However, the high sintering temperature required during the deposition of TiO2 layer and expensive Spiro-OMeTAD are limiting its commercial applicability. In this context, the combination of zinc sulfo-selenide (ZnS0.5Se0.5) (as ETL) which can be spray coated and inexpensive cuprous oxide (Cu2O) (as HTL) can serve as an alternative. This report computationally explores and compares the utility of the combination of ZnS0.5Se0.5 and Cu2O against that of TiO2 and Spiro-OMeTAD in terms of performance and reproducibility of MAPbI3 based PSC. The performance of optimized baseline models is quantitatively compared in terms of the values of performance metrics. Also, their performance is compared with respect to variations in bulk/interfacial defect density using the electrical and impedance spectroscopy characterizations. Further, their reproducibility is compared under variable carrier mobility of absorber layer. The optimized champion and mean power conversion efficiency of ZnS0.5Se0.5/Cu2O based cell are 25.6% and 25.3% respectively with standard deviation of 0.73% which is quite impressive and realistic when compared to the existing literature. The results obtained are quantitatively explained based on correlation between the cumulative effect of transit and recombination resistances evaluated using Nyquist profiles. The report systematically addresses the importance of ETL and HTL combination towards improving the performance and reproducibility of solution-processed PSCs.

Reducing Interfacial Losses in Solution-Processed Integrated Perovskite-Organic Solar Cells.

Low bandgap organic semiconductors have been widely employed to broaden the light response range to utilize much more photons in the inverted perovskite solar cells (PSCs). However, the serious charge recombination at the heterointerface contact between perovskite and organic semiconductors usually leads to large energy loss and limits the device performance. In this work, a titanium chelate, bis(2,4-pentanedionato) titanium(IV) oxide (C10H14O5Ti), was directly used as an interlayer between the perovskite layer and organic bulk heterojunction layer for the first time. Impressively, it was found that C10H14O5Ti can not only increase the surface potential of perovskite films but also show a positive passivation effect toward the perovskite film surface. Drawing from the above function, a smoother perovskite active layer with a higher work function was realized upon the use of C10H14O5Ti. As a result, the C10H14O5Ti-modified integrated devices show lower interfacial loss and obtain the best power conversion efficiency (PCE) of up to 20.91% with a high voltage of 1.15 V. The research offers a promising strategy to minimize the interfacial loss for the preparation of high-performance perovskite solar cells.

Fully solution-processed n-i-p type perovskite solar cells with efficiency over 19% enabled by a hydrophobic PEDOT:F interlayer and silver nanowire top electrode

Solution-processed top electrode is the key technology for the realization of fully solution-processed perovskite solar cells (PSCs). In this paper, we reported the preparation of fully-solution processed n-i-p type PSCs with spray-coated silver nanowires (AgNWs) top electrode. Experiment results demonstrated that low power conversion efficiency (PCE) of 16.00% with a low fill factor of 67.41% was obtained for the reference cell, when the AgNWs is directly coated on the 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) layer. This result indicates a charge extraction barrier at the Spiro-OMeTAD/AgNWs interface, which could be attributed to the poor compatibility between Spiro-OMeTAD and AgNWs layers. By inserting a thin layer of poly(3,4-ethylenedioxythiophene):perfluorinated sulfonic acid ionomers (PEDOT:F), a modified PEDOT with lower surface energy, the interface connection between Spiro-OMeTAD/PEDOT:F and AgNWs was improved, leading to an enhanced PCE of up to 19.11%. In addition, the PEDOT:F-based cells retained 64% of the initial PCE after operating at the maximum power point for 1800 h, whereas the reference cells retained only 30% of the initial PCE. The current work proved that PEDOT:F/AgNWs could be an excellent option for fully-solution processed n-i-p type PSCs.

Towards High Performance: Solution-Processed Perovskite Solar Cells with Cu-Doped CH3NH3PbI3.

Perovskite solar cells (PSCs) have demonstrated remarkable photovoltaic performance, positioning themselves as promising devices in the field. Theoretical calculations suggest that copper (Cu) can serve as an effective dopant, potentially occupying interstitial sites in the perovskite structure, thereby reducing the energy barrier and enhancing carrier extraction. Subsequent experimental investigations confirm that adding CuI as an additive to MAPbI3-based perovskite cells improves optoelectronic properties and overall device performance. Optimizing the amount of Cu (0.01 M) has been found to significantly enhance crystalline quality and grain size, leading to improved light absorption and suppressed carrier recombination. Consequently, the power conversion efficiency (PCE) of Cu-doped PSCs increased from 16.3% to 18.2%. However, excessive Cu doping (0.1 M) negatively impacts morphology, resulting in inferior optical properties and diminished device performance. Furthermore, Cu-doped PSCs exhibit higher stabilized power output (SPO) compared to pristine cells. This study underscores the substantial benefits of Cu doping for advancing the development of highly efficient PSCs.

Promoting solution-processed CdTe nanocrystal solar cells via rationally controlled copper doping

This study investigates Cu salt doped CdTe nanocrystals under various conditions, providing insight into the Cu doping mechanisms and the impact on device performance.

Post-Deposition In-Situ Passivation of AgBiS2 Nanocrystal Inks for High-Efficiency Ultra-Thin Solar Cells

Ternary chalcogenide AgBiS2 nanocrystals (NCs) have emerged as a new environmentally friendly material for non-toxic solution-processed solar cells, with a record efficiency of ~9%. To date, however, this has been...

Suppressing surface and bulk effect enables high efficiency solution-processed kesterite solar cells

Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) is a promising photovoltaic material due to its environmentally friendly composition and excellent photovoltaic performance. Unfortunately, open-circuit voltage (Voc) deficit and insufficient fill factor (FF) due to the interface and bulk carrier recombination have become major obstacle to further improve the device performance. A new effective strategy is proposed to simultaneously improve the front interface and suppress the CZTSSe absorber defects by introducing a thin ammonium sulfide layer on the absorber surface by a pre-soaking and spin-coating-annealing method. Through this strategy, the absorber surface is optimized by adding S and removing the secondary phase. At the same time, the diffusion of S into the bulk transforms the dominant deep VSe defect into shallower CuZn defect, which effectively reduces carrier recombination in the CZTSSe bulk and at the CZTSSe/CdS interface, prolongs minority carrier lifetime, facilitates carrier collection, and reduces charge loss. The optimized sulfurization treatment significantly improves VOC and FF to the point that device efficiency increases from 11.26% to 13.19%. These findings provide new insights into achieving higher efficiency in CZTSSe-based thin film solar cells by simultaneously optimizing the interface and bulk.

Parallel Planar Heterojunction Strategy Enables Sb2 S3 Solar Cells with Efficiency Exceeding 8 .

Solution-processed solar cells based on inorganic heterojunctions provide a potential approach to the efficient, stable and low-cost solar cells required for the terrestrial generation of photovoltaic energy. Antimony trisulfide (Sb2 S3 ) is a promising photovoltaic absorber. Here, an easily solution-processed parallel planar heterojunction (PPHJ) strategy and related principle are developed to prepare efficient multiple planar heterojunction (PHJ) solar cells, and the PPHJ strategy boosts the efficiency of solution-processed Sb2 S3 solar cells up to 8.32 % that is the highest amongst Sb2 S3 devices. The Sb2 S3 -based PPHJ device consists of two kinds of conventional planar heterojunction (PHJ) subcells in a parallel connection: Sb2 S3 -based PHJ subcells dominating the absorption and charge generation and CH3 NH3 PbI3 -based PHJ subcells governing the electron transport towards collection electrode, but it belongs to an Sb2 S3 device in nature. The resulting PPHJ device combines together the distinctive structural features of Sb2 S3 absorbing layer as a main absorber and the duplexity of well-crystallized/oriented CH3 NH3 PbI3 layer in charge transportation as an additional absorber, while the presence of perovskite does not affect device stability. The PPHJ strategy maintains the facile preparation by the conventional sequential depositions of multiple layers, but eliminates the normal complexity in both tandem and parallel tandem PHJ systems.

Exploration of Solution-Processed Bi/Sb Solar Cells by Automated Robotic Experiments Equipped with Microwave Conductivity.

Solution-processed inorganic solar cells with less toxic and earth-abundant elements are emerging as viable alternatives to high-performance lead-halide perovskite solar cells. However, the wide range of elements and process parameters impede the rapid exploration of vast chemical spaces. Here, we developed an automated robot-embedded measurement system that performs photoabsorption spectroscopy, optical microscopy, and white-light flash time-resolved microwave conductivity (TRMC). We tested 576 films of quaternary element-blended wide-bandgap Cs-Bi-Sb-I semiconductors with various compositions, organic salt additives (MACl, FACl, MAI, and FAI, where MA and FA represent methylammonium and formamidinium, respectively), and thermal annealing temperatures. Among them, we found that the maximum power conversion efficiency (PCE) was 2.36%, which is significantly higher than the PCE of 0.68% for a reference film without an additive. Machine learning (ML) and statistical analyses revealed significant features and their relationships with TRMC transients, thereby demonstrating the advantages of combining ML and automated experiments for the high-throughput exploration of photovoltaic materials.

Sb Doping Strategy to Promote Growth and Suppress Defects in Solution-Processed CZTSSe Solar Cells for Improved Optoelectronic Performance

Sb Doping Strategy to Promote Growth and Suppress Defects in Solution-Processed CZTSSe Solar Cells for Improved Optoelectronic Performance

(NH4)2S-induced improvement of CdS buffer layer for 15.52% efficiency solution-processed CIGS solar cell

(NH4)2S-induced improvement of CdS buffer layer for 15.52% efficiency solution-processed CIGS solar cell