PROGRAM DAY 1
OCTOBER 11TH, 2023
OCTOBER 11TH, 2023
Opening session by the organizer of the Carbon Club and the Project Coordinator of DIAMOND
Our organizer, Lukas Wagner will give an introductory statement to commence the session.
After, Uli Würfel, Project Coordinator of the DIAMOND EU Project will give a brief talk on said project.
Session 1 – Materials and Cell Design Improvement
Moderated by Lukas Wagner, University of Marburg
Tian Du, FAU Erlangen-Nürnberg
"Bulk and interfacial optimization towards high-efficiency, fully printable perovskite photovoltaics"
Design of hole-transporting layer (HTL) needs to take both perovskite/HTL and HTL/electrode interfaces into consideration. For printable carbon electrode, formation of ohmic contact with the HTL is a critical performance-enhancing factor. We show that the properties of HTL that facilitate ohmic contact formation may reduce open-circuit voltage (VOC): doping of HTL causes perovskite surface recombination whilst shallow HOMO level of the HTL induces interfacial quasi-Fermi level bending. In this regard, we propose a hole-transporting bilayer (HTbL) configuration, prepared by sequentially blade-coating two organic semiconductors between perovskite and carbon. With the outer HTL enhancing hole extraction to carbon whilst the inner HTL mitigating perovskite surface recombination, fill factor and VOC of the carbon-electrode perovskite solar cells can be improved simultaneously.
Luke Sutherland, CSIRO
"Versatile Carbon Electrodes for Record Small, Large, Rigid, and Flexible Perovskite Solar Cells"
The high-throughput fabrication of perovskite solar cells (PSCs) cannot be realized until the costly, low-throughput evaporated metal electrode is replaced by roll-to-roll (R2R) printable and vacuum-free electrodes. We introduce a novel method to fabricate, and deposit printed carbon-based electrodes that avoids potential loss of PSC performance due to solvent migration from the pastes. Flexible, R2R-fabricated carbon-based PSCs (c-PSCs) with record power conversion efficiencies (PCEs) of up to 16.7% were produced by vacuum-free deposition of all active layers, apart from the transparent conductive electrode. This performance compares very favorably with that of control flexible PSCs comprising an evaporated gold electrode which displayed record PCEs of up to 17.4%. The flexible c-PSCs demonstrate outstanding mechanical stability, with retention of more than 90% of their initial PCE after 3000 cyclic bends. Furthermore, we have developed a means to deposit the fully printed electrodes onto rigid, glass-based c-PSCs to achieve efficiencies of over 20% for small area cells (0.16 cm² active area), and over 18% for large area (~ 1 cm²). This readily scalable method provides a pathway forward to improve the production throughput and cost-effectiveness of PSC fabrication by removing the need for costly gold evaporation processes whilst still retaining exceptional photovoltaic performance and believe this method can be readily adopted to demonstrate record-breaking PSCs incorporating printed electrodes.
Shiyu Wang, Shenzhen Polytechnic University
"Mesoporous-Carbon-Based Fully-Printable All-Inorganic CsPbBr3 Perovskite Solar Cells with Ultrastability under High Temperature and High Humidity"
The pursuit of commercializing perovskite photovoltaics has been driving the development of various scalable perovskite crystallization techniques. Among them, gas-quenching has been demonstrated as the most promising crystallization approach due to its capability for high-throughput deposition of perovskite films. However, the perovskite films prepared by gas-quenching assisted blade coating are susceptible to a high number of pinholes, defects, and significant inhomogeneity, owing to the limited understanding of perovskite crystallization behaviour and thus lack of robust methodologies to improve it. Here, we devise in-situ optical spectroscopies integrated into a doctor blading setup that allows to real-time monitor film formation during the gas-quenching process. We first elucidate the essential role of gas quenching treatment in achieving a smooth and compact perovskite film by controlling the nucleation rate. After that, we revisit and unravel, by means of in-situ techniques along with the assistance of phase-field simulations, the role of excessive methylammonium iodide (MAI) in the precursor solution in increasing grain size by accelerating crystal growth rate. Our results show that a tailored amount of excessive MAI is dominantly controlling the growth rate of nanocrystals, which is critical to achieving high-quality perovskite films with improved crystallinity, preferred orientation and reduced defect density. Eventually, fully-printed solar cells with an impressive champion PCE of 19.50% and mini-modules with a PCE of 15.28% are achieved. These results emphasize the growth rate can be optimized independently from the crystal nucleation rate for developing efficient fully printed perovskite photovoltaic.
Tino Lukas, University of Oxford
“High Throughput and Scalable p-i-n Perovskite Solar Cells"
Solar cells with lead halide perovskites (PSC) have improved significantly in their performance of lab-scale devices. But the record-breaking lab scale PSC rely on evaporated noble metals as electrode materials. This expensive and slow process impedes the direct translation of the laboratory success of PSC into real-world applications. Further, all metal electrodes react with the perovskite layer and lower the stability of the devices. Strong candidates to replace evaporated metal electrodes are carbonbased materials deposited via solution processes which promise cheaper, quicker to make, and more stable electrodes. Most publications on carbon electrodes are on devices in either the normal n-i-p or the hole-transport-layer free architecture. However, the transport layers used in n-i-p devices are frequently linked to stability issues like the photoactive TiO2 and Spiro-OMeTAD which is frequently doped with hygroscopic salt. We have realised a solar cell in the more stable p-i-n architecture and without high vacuum processes via ambient carbon blade coating for the electrode. All layers in these devices are solution processed but an SnO2 layer, which is deposited by atomic layer deposition (ALD). ALD is quicker than evaporation and is compatible with higher throughput processes. Further, SnO2 and carbon are inert to the halides. This might pave the way to cheaper, more industrial viable, and more stable PSC.
Priyanka Kajal, NTU
"Impact of carbon black selection on performance of Carbon-Based Perovskite Solar Cells"
Carbon electrode is the major component of the carbon based perovskite solar cells. There are numerous reports about the effect of the graphite size, amount of carbon black etc, however the selection of the carbon black type remains a significant challenge. In this study, we investigated the impact of the carbon black selection on the properties of electrode and device performance. Three most commercially available carbons blacks i.e. Vulcanized, meso and super P carbon blacks were tested. Our findings revealed that the utilization of vulcan carbon black in carbon paste results in higher porosity, better perovskite wettability, better adhesion. As a result, vulcanized carbon electrodes shows lower sheet resistance of 11.0 Ω/cm² than meso (15.3 Ω/cm²) and super P (22.0 Ω/cm²). Additionally Vulcan carbon based solar cells shows higher PCE of 12.55%. Vulcan devices sustains their performance after aging of un-encapsulated devices over 30 days at RH of 75%. This study thus highlights the critical role of carbon black selection on improving the performance and stability of carbon based perovskite solar cells.
Session 2 – Sustainability
Moderated by Jan Christoph Goldschmidt, University of Marburg
Andreas Hinsch, Fraunhofer ISE
"A brief guideline on how to overcome challenges in the development of sustainable perovskite solar cells based on carbon counter electrodes"
Elena Akulenko, University of Turku
“Revival of Carbon-Based Perovskite Solar Cells Using Green Solvents: An Approach Towards Sustainable Renewable Energy”
Perovskite solar cells (PSCs) are continuously attracting attention due to their low cost and outstanding performance . Nevertheless, the development of PSCs should be approached cautiously to preserve rare materials and prevent harmful chemical releases into the environment . Due to their complex multicomponent structure, recycling PSCs is challenging. We have shown that the porosity of the back contact and its stability play a crucial role in determining the feasibility of PSC revival . The highly stable and mesoporous structure of carbon-based perovskite solar cells (C-PSCs) makes them exceptionally well-suited for the revival process.
We introduce liquid methods, which are generally more suitable for scalability than previously reported gas treatments , to evaluate the potential of various carbon electrode structures for revival. Typically, revival involves washing out and reloading perovskite, a process that requires careful consideration of solvent choice. We investigate the performance of a non-toxic solvent, γ-Valerolactone (GVL), renowned for its eco-friendly properties and has shown its competitive efficiency in PSCs . Our findings suggest that GVL, an attractive greener option compared to toxic aprotic solvents like DMF and DMSO, holds promising potential for reviving C-PSCs.
Furthermore, the study sheds light on the significance of the C-PSC fabrication method in achieving durable top contact during revival processes. Remarkably, structures with an additional amount of zirconia nanoparticles exhibit high stability during the washing out step, even in the presence of strong solvents such as DMF. It is hypothesized that zirconia nanoparticles and their sintering act as a cohesive agent for carbon particles, thus rendering them sufficiently robust to endure the solvents.
The consideration of non-toxic solvents like GVL provides a more environmentally responsible approach to PSC recycling. The development of effective, scalable, and eco-friendly revival techniques for C-PSCs brings us closer to a cleaner and greener future for renewable energy.
Woraprom Passatorntaschakorn, Chiang Mai University
“Surface Passivated Carbon Electrodes for Efficient and Stable Flexible Perovskite Solar Cells”
Flexible carbon electrode-based perovskite solar cells (C-PSCs) have drawn significant attention in various niche products due to their high power-per-weight, simple fabrication process, excellent stability, and cost-effectiveness. However, reports of flexible C-PSCs are relatively rare because the mismatch between the C-PSCs structure and the carbon electrodes leads to high series resistance and carrier recombination resulting from a lack of interface contact between the hole transporting layer (HTL) and carbon electrodes. Herein, we introduce reduced graphene oxide (rGO)-Thai coffee ground waste CQDs-polyethylene glycol (PEG) composites to serve as a passivated macro-porous gap in carbon paste using a green and simple ethanol solvent interlacing process. The rGO-CQDs-PEG composites passivated carbon electrode exhibits high conductivity and excellent flexibility, leading to tight adhesion onto the HTL through the heat-press transfer method. The introduction of the passivated carbon electrode not only forms a self-adhesive electrode and reduces the defect density of the carbon film but also modifies the energy band arrangement with surface dipole formation between the HTL and the carbon electrode, thus promoting beneficial carrier charge transfer. The passivated carbon electrode serves well as counter electrodes for efficient and stable flexible C-PSCs with an area of 1.00 cm2, exhibiting remarkable performance under 1 sun and LED illuminations, along with long-term stability and outstanding bending durability. The findings of this work provide a basis for developing a cost-effective, sustainable, and easily accessible approach for carbon electrode preparation with improved performance, lightweight, and long-term stability, making them suitable for nondestructive encapsulation and indoor applications, thereby paving the way towards future commercialization.
Fabian Schmitz, Justus Liebig University Giessen
"Enhancing Stability and Band Alignment in Cs2AgBiBr6-based HTM Free Solar Cells by Applying a 2D Surface Modification"
Cs2AgBiBr6 is an inorganic lead-free double perovskite in which the divalent Pb2+ has been substituted
by equal amounts of monovalent Ag+ and trivalent Bi3+. In contrast to other lead-free perovskite materials such as tin-based perovskites, this material can be characterized by a high environmental
stability and low toxicity. These advantageous properties make Cs2AgBiBr6 a valuable material for indoor photovoltaics to power the Internet of Things (IoT). However, properties such as its large indirect band gap, strong exciton binding energy and electron-phonon coupling, as well as fast surface charge recombination still limit its power conversion efficiency (PCE) to below 3% in
photovoltaic devices to date.
In this work, we combined a surface modification of the perovskite thin film using butylammonium bromide (BABr) to create a capping layer of a two-dimensional (2D) perovskite phase with the application of a carbon-based electrode that replaced the typically utilized hole transport material
(HTM) and gold electrode in solar cells. The 2D perovskite capping layer, whose existence was proved by XRD, XPS and contact angle measurements, serves several purposes that we investigated: It passivates the perovskite thin film to reduce surface recombination, the material is protected from humidity due to the capping layer’s hydrophobicity, and the 2D perovskite possesses an increased valence band maximum, thus optimizing the band alignment towards the back electrode.
Furthermore, the carbon back electrode is prepared from an upcycled industrial biowaste via screen printing.
In summary, we were able to boost the efficiency of Cs2AgBiBr6 solar cells by engineering the 2D capping layer’s thickness to achieve an optimized band alignment towards the carbon back electrode. Thus, we present an end-of-waste strategy to fabricate non-hazardous, highly stable, and cost-efficient photovoltaics.
Session 3 – INDUSTRY TALKS
Moderated Yue Hu, University of Edinburgh
Toby Meyer, Solaronix
"The Fun and Challenges of all Printed Perovskite Modules"
Presentation the concept of Solaronix’s all-printed perovskite solar cells & modules based on mesoporous TiO2 & ZrO2 layers and a porous carbon as back contact.
All the metal oxide layers as well as the carbon electrode are deposited by screen-printing, making the production very fast.
Once these layers are thermally cured, the methylammonium lead iodide perovskite is inkjet printed to infiltrate the whole porous structure, completed afterwards by a glass as back seal.
This solar cell architecture allows for lab-cells with up to 15% PCE and 13% PCE on 57 cm² aperture area mini-modules, being assembled on our semi-automatic line.
The challenges to be addressed are efficiency increase, reverse bias behavior, and durability at elevated temperatures. Several EU-project Solaronix’s are involved in are aimed to solve some of these tasks.
Eric Bergmann, Rayleigh Solar Tech
"Scaling progress towards the commercialization of planar carbon perovskite solar modules"
Konrad Wojciechowski, Saule Technologies
"Perovskite photovoltaic technology on flexible substrates"
Metal halide perovskites constitute a very attractive class of materials for optoelectronic applications, such as solar cells, light emitting diodes, lasers and photodetectors. Most notably, solid-state photovoltaic devices based on these materials have reached power conversion efficiencies (PCEs) exceeding 26% within only a decade of academic research.
Perovskite solar cells have a great market potential, but there still remain few challenges, which need to be resolved to prove viability of the technology. Some of the well-known issues include material stability. Furthermore, cost-effective, reliable fabrication process capable of delivering highly efficient, large-area perovskite modules is of paramount importance.
Carbon was demonstrated as an effective back-contact electrode material for the perovskite solar cells, a possible alternative to metallic layers. These carbon electrodes can be prepared as composite films at low temperature processing, enabling facile scalability. High efficiencies and largely improved stabilities were reported for this type of devices. Additionally, thanks to favourable optoelectronic properties of carbon components, device architectures without the use of hole transport materials were demonstrated, further simplifying the fabrication process and reducing the costs.
This talk will outline some architectural and compositional developments in flexible perovskite solar cells. These devices successfully passed IEC-based accelerated aging tests, including damp heat aging. Furthermore, industrial opportunities of perovskite PV technology, focusing on new value propositions and market versatility will be discussed.
Session 4 – Device performance optimization
Moderated Ali Emami, University of Porto
Dongmei Li, Chinese Academy of Sciences
"Carbon Materials for Perovskite Solar Cells"
Perovskite solar cells (PSCs) have received more and more attention because of its high efficiency, low cost and easy fabrication. So far, 26% power-conversion-efficiency (PCE) has been achieved for PSCs. However, stability problem of this emerging photovoltaics, including moisture, heat, UV light and electricity stabilities are still an obstacle for further commercialization. People have contributed a lot of efforts to solve these problems. Carbon materials are good alternative to Au electrodes for n-i-p type PSCs due to its low cost, printable, suitable work function. Different carbon materials have been attempted in PSCs, however, the cell performance of carbon-based devices is still unsatisfied mainly due to poor interfacial contact and poor conductivity. In our group, we have been working on the application of carbon materials on emerging solar cells for over fifteen years. Recently, we developed low-temperature flexible carbon films, which were used to fabricate inorganic CsPbI3 PSCs and hybrid PSCs, respectively. Over 24% PCE of hybrid PSCs and over 19% PCE of CsPbI3 PSCs have been achieved. We also designed a full-carbon electrode (F-CE), which exhibited effective thermal radiation to reduce the temperature of the operating cell by about 10°C, both from theoretical simulation and experimental testing. Especially, the CsPbI3 PSCs exhibited no efficiency degradation after 2000 h continuous operational tracking.
Gerrit Boschloo, Uppsala University
“Low-temperature processed carbon-based perovskite solar cells: effects of inclusion of a polymeric hole conductor and surface modifications”
Low-temperature-processed carbon-based perovskite solar cells (C-PSCs) are promising photovoltaic devices, because of their good stability, low cost, and simple preparation methods, which allow for scalable processing. Herein, C-PSCs with the n-i-p structure are prepared, using a SnO2 nanoparticle ﬁlm as the electron-selective contact, MAPbI3 perovskite as the intrinsic absorber layer, and a carbon layer as the hole-selective layer and conductor. Carbon is, however, not an ideal hole-selective layer and it is found that improved solar cell performance can be obtained by introducing a polymeric hole conductor between the perovskite and the carbon layer. Speciﬁcally, undoped poly(3-hexylthiophene) (P3HT) is used for this purpose, as it is stable and highly hydrophobic. For ITO/SnO2/MAPbI3/carbon devices, a solar cell efﬁciency of up to 12.8% is obtained, increasing up to 15.7% with the inclusion of a P3HT layer. In comparison, ITO/SnO2/MAPbI3/P3HT/Au devices performed rather poorly (up to 11.7%). Unencapsulated C- P3HT/carbon devices did not show any degradation in solar cell performance upon storage for 1 month in low humidity, while they maintain 70% of their initial efﬁciency after 900 h at 82 C in air.
In order to reduce the number of fabrication steps, we successfully included P3HT into the antisolvent, resulting in stable devices with PCE up to 12.2%, compared to 10.6% for devices without P3HT. We also studied mixed ion perovskites prepared by a two-step method. ITO/SnO2/(Cs0.05FA0.54MA0.41)Pb(I0.98Br0.02)3/P3HT/carbon devices yielded a PCE of 14.0%, while hexyl trimethylammonium bromide (HTAB) top surface modification improved it up to 16.1%.
We will analyze losses in our investigated systems and present our ideas and strategies for further improvement of C-PSC.
Uma Kousalya Dangudubiyyam, Fraunhofer ISE
“Interfacial passivation to enhance the performance and stability of carbon-based perovskite solar cells”
Perovskite solar cells (PSCs) have achieved remarkable efficiencies, but challenges regarding the devices’ longterm performance remain to be a critical concern for commercialization. Carbon-based PSCs (C-PSCs) offer potential stability improvements over PSCs with metal electrodes, which are the cause for some of the observed device degradation mechanisms, e.g., diffusion of metal atoms into the photoactive layer, redox reactions with perovskite and corrosion of the metal electrode by reaction with perovskite decomposition products 1,2 . Nevertheless, the power conversion efficiency (PCE) of C-PSCs is still lower, e.g., due to nonradiative recombination at interfaces. Interfacial passivation methods can be utilized to alleviate this problem and enhance C-PSC performance. In this study, the alkyl ammonium salt N-hexyltrimethylammonium bromide (N-HTABr) is employed as a passivation layer between perovskite and carbon. In comparison to cells without passivation layer, HTL-free C-PSCs with N-HTABr have shown VOC enhancement by nearly 60 mV, resulting in a PCE of 15.3% for the champion cell. SEM, XRD and UV-Vis spectroscopy were implemented to understand the structural, morphological, and optical changes in the perovskite layer with N-HTABr. It is seen that passivated C-PSCs have a higher crystallinity with reduced residual PbI2, creating a low-dimensional/3D hybrid perovskite interface. Additionally, from material characterizations of phase-pure materials synthesized from lead halides and N-HTABr, it is understood that N-HTABr creates 1D perovskite on top of 3D perovskite following surface treatment of the latter. The corresponding band gap widening is suggested to form an energy barrier for electron transport to the carbon electrode, leading to increased hole selectivity and thus reduction of nonradiative recombination and increase in VOC. Furthermore, unencapsulated HTL-free C-PSC with N-HTABr passivation showed an increase in efficiency from 15.3% to 16.7% after storing in ambient air.
Jessica Barichello, CHOSE
"The effect of water in Carbon-Perovskite Solar Cells"
A hot topic is the perovskite solar cells’ (PSC) sensitivity to water and humidity, a challenge that still compromises a full commercialization of perovskite based-PV devices. H2O irreversibly destroys perovskite materials and moisture negatively influences the long-term stability and the lifetime of PSCs. In order to develop control strategies to mitigate the problem, comprehending how H2O influences the perovskite materials is also important. Indeed, a modest amount of water may work to facilitate the nucleation and the crystallization of the perovskite, improving the quality of the deposited perovskite film and enhancing PSC performance. A study on water pre-treatment before perovskite deposition based on carbon counterelectrode is presented. Carbon materials are cheaper than the most utilized hole transport material (HTM) (e.g. Spiro-OmeTAD) and top-electrode (e.g. gold), resulting in a reduction of the cell cost. Moreover, it has been found that Spiro-OmeTAD is not stable under thermal stress and gold diffuses in the device structure when exposed to continuous illumination. Firstly, a fully printed optimized structure with an Alumina insulating layer carbon-based HTM-free PSC is presented. Then, we present a study where the water pretreatment improves pore filling, leads to a reduction of charge recombination, and improves the conversion of PbI2 crystals into perovskite. The water pre-treatment permits to obtain an average efficiency increasing of 16% with respect to cells without water pre-treatment.
Wenjun Wu, East China University of Science & Technology
“Chiral Molecular Environment Influences the Selective Coordination of Cysteine to Halogen Vacancies in Perovskite"
Amino acids with functional groups in a single molecule have been proposed as passivators for perovskite solar cells (PSCs). However, the impact of chirality-induced differences in PSCs, resulting from subtle changes in the molecular environment between enantiomers of amino acids, has received little attention. In this study, L- and D-cysteine were added to printable PSCs, achieving efficiencies of 17.41% and 15.12% respectively. DFT analysis revealed that the chiral molecular environment of L-cysteine enhanced charge transfer, improved Pb2+ coordination, and inhibited recombination. Additionally, L-cysteine showed advantages in crystallization, stability, and light capture. This study introduces a novel research pathway extending the passivation mechanism from functional groups to the molecular environment.
Session 5 – Materials and cell design improvement
Moderated Sam March, Rayleigh Solar Tech
Lioz Etgar, The Hebrew University of Jerusalem
"Bifacial Mesoscopic triple oxide perovskite solar cells"
In this work, I will present new concepts related to Mesoscopic triple oxide perovskite solar cells. Recently we developed unique fully printable mesoporous indium tin oxide (ITO) perovskite solar cell. In this structure, the perovskite is not form a separate layer but fills the pores of the triple-oxide structure. One of the advantages of this solar cell structure is the transparent contact (mesoporous ITO) which permits the use of this cell structure in bifacial configuration without the need for additional layers or thinner counter electrodes. We performed full characterizations on both sides (i.e. ITO-side and glass-side) and elucidated the solar cell mechanism, where the glass side shows 15.3% efficiency compared to 3.8% of the ITO-side. Further study of the mechanism shows that the dominant mechanism when illuminating from the glass-side is Shockley-Read-Hall recombination in the bulk, while illuminating from the ITO-side show recombination in multiple traps and inter gap defect distribution which explains the poor PV performance of the ITO-side. Electrochemical impedance spectroscopy shed more light on the resistance and capacitance. Finally, we demonstrate 18.3% efficiency in bifacial configuration. This work shows a fully printable solar cell structure which can function in bifacial configuration.
Hadi Mohammadzadeh, Fraunhofer ISE
"Modification and Lamination of Solvent-free Carbon Back-Electrodes for Fabrication of Efficient Perovskite Solar Cells"
Carbon is being explored as an alternative to metal electrodes in perovskite solar cells (PSCs) to increase the stability, lower the carbon footprint, and reduce the cost of production. Typically, it is applied by blade coating or printing a paste form. However, the solvents in the paste can have adverse effects on underlying interfacial layers and can e.g. dissolve the commonly applied hole transport material (HTM) Spiro-OMeTAD in n-i-p cell architectures. One solution is the press transfer of dried carbon films, but previous studies lacked reproducibility or needed other materials as support, e.g. metal foils. 
In this study, we investigated press-transfer for fabrication of carbon-based PSCs in n-i-p architecture and discovered an extremely rough surface and uneven thickness of the carbon layer. This leads to a poor connection between the carbon layer and the underlying surface when using plate-to-plate press, resulting in higher series resistance in comparison with blade coating or printing. To investigate this, we used 3D laser scanning microscopy, mathematical modeling and electro-optical characterizations. By optimizing the pressing process, we achieved 95% efficiency compared to gold-based cells with Spiro-OMeTAD, above the efficiency of cells based on blade-coated carbon with P3HT as HTM.
However, even after optimization, the roughness of the carbon layer was suspected to still limit the device performance. Thus, in an attempt to increase the electrodes’ conductivity, we explored carbon modification based on a so-called “solvent exchange” process. Here, we modified the carbon films with a highly conductive PEDOT:PSS (Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) formulation. The modified carbon showed a work function increase of 0.5 eV and a sheet-resistance decrease of about 60% compared to unmodified carbon. Although the efficiency of the cells made from the modified carbon is still below our expectations, this approach demonstrates its potential and opens up new possibilities to achieve higher efficiencies.
Salma Zouhair, Fraunhofer ISE
“Minimizing Recombination Losses in Perovskite Solar Cells with Carbon Electrode Using the 3D/2D Concept”
The absence of hole selective layers (HSLs) in carbon electrode-based perovskite solar cells (C-PSCs) causes significant losses to the performance at the interface between the carbon electrode and the perovskite photo-absorber. Interface engineering using 2D halide perovskites has demonstrated successful surface passivation of the defects and trap states in 3D perovskite thin films, making it an appealing alternative.
Here we incorporate an octylammonium iodide salt on a FAPbI3 3D perovskite absorber in HSL free C-PSCs. We confirm the formation of the resulting 2D perovskite layer through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and microscopically resolved photoluminescence
(PL) microscopy measurements. Ultraviolet photoelectron spectroscopy (UPS) measurements allowed to inspect the energy level alignment between the 3D and 2D perovskite films, which further confirmed the presence of a high band gap 2D perovskite layer at the interface between the photo-absorber and the carbon electrode, allowing it to behave as an electron-blocking layer (EBL), effectively suppressing electron back transfer towards the carbon counter electrode. Accordingly, C-PSCs with 2D perovskite EBL showed an improved overall performance, recording a 65 mV increase in photovoltage and 10%
enhancement of the fill factor (FF), achieving an efficiency of 18.5% for the champion device. Further investigation using electrochemical impedance spectroscopy (EIS) and light dependent JSC-VOC analysis confirmed the reduction of carrier loss by non-radiative recombination. The C-PSC with 2D perovskite EBL also maintained 82% of its initial efficiency after 500 hours of constant 1-sun illumination in a nitrogen filled environment, compared to 60% recorded for the device without 2D perovskite EBL. Hence in this study we showcase the immense potential of 2D perovskites in minimizing interfacial recombination losses due to the lack of an HSL in C-PSCs. We also highlight that its electron-blocking function could play a crucial role in advancing the practical development of fully printable C-PSCs.
Jacob Wall, Arizona State University
“Carbon Electrode with Sputtered Au Coating for Efficient and Stable Perovskite Solar Cells”
Perovskite solar cells (PSCs) show great promise as a low-cost, high-efficiency solar technology. However, the widespread adoption of PSCs is hindered by the need for noble electrodes, such as Au, through thermal evaporation. Unfortunately, sputtered Au electrodes on PSCs can cause damage to the organic hole transport layer and the perovskite layer, limiting device stability. We present an innovative approach to overcome these challenges by introducing a simple, yet effective sputtered gold nanoparticle decorated carbon electrode for the fabrication of efficient and stable planar PSCs. The novel composite electrode design offers several advantages over traditional Au-based electrodes, providing a commercialization pathway for perovskite solar modules. To construct the composite electrode, a thin Au layer is sputtered onto a doctor-bladed coated carbon electrode, enabling direct application to the perovskite semicells through mechanical stacking. By optimizing the gold thickness in the electrode, we achieved a remarkable power conversion efficiency (PCE) of 16.87%, surpassing the reference device’s PCE of 12.38%. This enhancement in PCE highlights the potential of the composite electrode to boost performance of PSCs, rendering them superior in the renewable energy landscape. Beyond efficiency improvements, the composite electrode-based PSC exhibits exceptional stability under harsh environmental conditions. Remarkably, the device demonstrated 96% performance retention after exposure to humid conditions (50–60%) for approximately 100 hours without the need for encapsulation. This stability performance underscores the practicality and reliability of the sputtered gold nanoparticle decorated carbon electrode in real-world applications. In summary, our research showcases successful integration of carbon-based electrodes with sputtered gold nanoparticles to create efficient and stable perovskite solar cells. By addressing the limitations associated with noble electrodes, this innovation opens new avenues for large-scale manufacturability and commercial viability of perovskite solar modules. These findings are a significant step towards achieving cost-effective and sustainable photovoltaic solutions for the global energy demand.
Saivineeth Penukula, Arizona State University
“Reduction of Mobile Ion Concentration in Metal Halide Perovskites using Carbon Electrode”
Metal halide perovskites (MHPs) have shown significant growth in power conversion efficiencies over the past decade along with the demonstration of low processing costs. However, MHPs are at a crossroads with commercialization because of operational instabilities. Ion migration is one of the main reasons that causes this instability and degradation in MHPs. In this work we demonstrate the methods in which ion migration in perovskite solar cells (PSCs) and MHP thin films can be quantified in terms of the number of mobile ions present in the lattice (mobile ion concentration – No) and how fast they are moving in the lattice (ionic mobility – µ). We also demonstrate that these measurements can be performed directly on MHP thin films with the help of a C electrode on top of the thin film which gives the capability to quantify ion migration without the influence of interfaces. We study the effect of introducing small alkali metal A-site cation additives (e.g., Na+, K+, and Rb+) into the MHP lattice both in MHP thin films and PSCs. We show a reduction of No in PSCs when a C top electrode is used when compared to Ag electrode in both films and devices, which is consistent both in the case of a solvent based C electrode and a solvent free C electrode as shown in the Figure 1. We show that the influence of moisture and cation additive on No is less significant than the choice of top electrode in PSCs. This work gives design principles regarding the importance of passivation and the effects of operational conditions on ion migration.