Toward Commercialization of Stable Devices: An Overview on Encapsulation of Hybrid Organic-Inorganic Perovskite Solar Cells

Identification and Dynamics of Microsecond Long-Lived Charge Carriers for CsPbBr3 Perovskite Quantum Dots, Featuring Ambient Long-Term Stability

We analyze the stability and photophysical dynamics of CsPbBr3 perovskite quantum dots (PeQDs), fabricated under mild synthetic conditions and embedded in an amorphous silica (SiOx) matrix (CsPbBr3@SiOx), underscoring their sustained performance in ambient conditions for over 300 days with minimal optical degradation. However, this stability comes at the cost of a reduced photoluminescence efficiency. Time-resolved spectroscopic analyses, including flash-photolysis time-resolved microwave conductivity and time-resolved photoluminescence, show that excitons in CsPbBr3@SiOx films decay within 2.5 ns, while charge carriers recombine over approximately 230 ns. This longevity of the charge carriers is due to photoinduced electron transfer to the SiOx matrix, enabling hole retention. The measured hole mobility in these PeQDs is 0.880 cm2 V-1 s-1, underscoring their potential in optoelectronic applications. This study highlights the role of the silica matrix in enhancing the durability of PeQDs in humid environments and modifying exciton dynamics and photoluminescence, providing valuable insights for developing robust optoelectronic materials.

Photo-Cross-Linked Fullerene-Based Hole Transport Material for Moisture-Resistant Regular Fullerene Sandwich Perovskite Solar Cells

Despite the high efficiencies currently achieved with perovskite solar cells (PSCs), the need to develop stable devices, particularly in humid conditions, still remains. This study presents the synthesis of a novel photo-cross-linkable fullerene-based hole transport material named FT12. For the first time, the photo-cross-linking process is applied to PSCs, resulting in the preparation of photo-cross-linked FT12 (PCL FT12). Regular PSCs based on C60-sandwich architectures were fabricated using FT12 and PCL FT12 as dopant-free hole transport layers (HTLs) and compared to the reference spiro-OMeTAD. The photovoltaic results demonstrate that both FT12 and PCL FT12 significantly outperform pristine spiro-OMeTAD regarding device performance and stability. The comparison between devices based on FT12 and PCL FT12 demonstrates that the photo-cross-linking process enhances device efficiency. This improvement is primarily attributed to enhanced charge extraction, partial oxidation of the HTL, increased hole mobility, and improved layer morphology. PCL FT12-based devices exhibit improved stability compared to FT12 devices, primarily due to the superior moisture resistance achieved through photo-cross-linking.

Charge Carrier Dynamics at the Interface of 2D Metal-Organic Frameworks and Hybrid Perovskites for Solar Energy Harvesting

Interfacing perovskites with two-dimensional materials such as metal-organic frameworks (MOFs) for improved stability and electron or hole extraction has emerged as a promising path forward for the generation of highly efficient and stable solar cells. In this work, we examine the structural properties and excitation dynamics of two MOF-perovskite systems: UMCM309-a@MAPbI3 and ZrL3@MAPbI3. We find that precise band alignment and electronegativity of the MOF-linkers are necessary to facilitate the capture of excited charge carriers. Furthermore, we demonstrate that intraband relaxation of hot electrons to the MOF subsystem results in optically disallowed transitions across the band gap, suppressing radiative recombination. Furthermore, we elucidate the key mechanisms associated with improved structural stability afforded to the perovskites by the two-dimensional MOFs, highlighting the necessity of broad surface coverage and strong MOF-perovskite interaction.

Structural Disorder in Higher-Temperature Phases Increases Charge Carrier Lifetimes in Metal Halide Perovskites

Solar cells and optoelectronic devices are exposed to heat that degrades performance. Therefore, elucidating temperature-dependent charge carrier dynamics is essential for device optimization. Charge carrier lifetimes decrease with temperature in conventional semiconductors. The opposite, anomalous trend is observed in some experiments performed with MAPbI₃ (MA = CH₃NH₃⁺) and other metal halide perovskites. Using ab initio quantum dynamics simulation, we establish the atomic mechanisms responsible for nonradiative electron-hole recombination in orthorhombic-, tetragonal-, and cubic MAPbI₃. We demonstrate that structural disorder arising from the phase transitions is as important as the disorder due to heating in the same phase. The carrier lifetimes grow both with increasing temperature in the same phase and upon transition to the higher-temperature phases. The increased lifetime is rationalized by structural disorder that induces partial charge localization, decreases nonadiabatic coupling, and shortens quantum coherence. Inelastic and elastic electron-vibrational interactions exhibit opposite dependence on temperature and phase. The partial disorder and localization arise from thermal motions of both the inorganic lattice and the organic cations and depend significantly on the phase. The structural deformations induced by thermal fluctuations and phase transitions are on the same order as deformations induced by defects, and hence, thermal disorder plays a very important role. Since charge localization increases carrier lifetimes but inhibits transport, an optimal regime maximizing carrier diffusion can be designed, depending on phase, temperature, material morphology, and device architecture. The atomistic mechanisms responsible for the enhanced carrier lifetimes at elevated temperatures provide guidelines for the design of improved solar energy and optoelectronic materials.

How varying surface wettability of different PEDOT:PSS formulations and their mixtures affects perovskite crystallization and the efficiency of inverted perovskite solar cells

The physico-chemical interaction, surface, and electrical properties of hole transport layers (HTLs) significantly affect the wettability and film crystallization of the deposited perovskite and the corresponding performance of inverted perovskite solar cells (PSCs). One of the most frequently used HTLs for inverted PSCs is poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). Various commercial PEDOT:PSS formulations have already been tested as HTLs. Until now mixtures of these remained rather unexplored. In this study, three commercially available PEDOT:PSS formulations (PH, PH1000, and AI4083), as well as three mixtures (PH:PH1000, PH:AI4083, and PH:PH1000:AI4083; in a 1 : 1 and 1 : 1 : 1 ratios) were used as HTLs to investigate the crystallization of perovskite films and the performance of associated PSCs. Of the three formulations, PEDOT:PSS PH showed better perovskite crystallization, resulting in better solar cell performance followed by both PH:AI4083 and PH:PH1000:AI4083 layers. The pioneering work on mixing PEDOT:PSS resulted in new combinations of PEDOT:PSS, with new properties (work function, surface wettability, and roughness) which are very important parameters for perovskite crystallization and corresponding device efficiencies and stabilities. All PSCs that use the mixed PEDOT:PSS as HTLs revealed higher fill factor and open-circuit voltage values above 900 mV, which is not the same except for PEDOT:PSS PH. As a result, we believe that such a mixing strategy could aid in the creation of various PEDOT:PSS combinations with tuneable properties for certain applications.

Encapsulation and Outdoor Testing of Perovskite Solar Cells: Comparing Industrially Relevant Process with a Simplified Lab Procedure

Perovskite solar cells (PSCs) have shown great potential for next-generation photovoltaics. One of the main barriers to their commercial use is their poor long-term stability under ambient conditions and, in particular, their sensitivity to moisture and oxygen. Therefore, several encapsulation strategies are being developed in an attempt to improve the stability of PSCs in a humid environment. The lack of common testing procedures makes the comparison of encapsulation strategies challenging. In this paper, we optimized and investigated two common encapsulation strategies: lamination-based glass-glass encapsulation for outdoor operation and commercial use (COM) and a simple glue-based encapsulation mostly utilized for laboratory research purposes (LAB). We compare both approaches and evaluate their effectiveness to impede humidity ingress under three different testing conditions: on-shelf storage at 21 °C and 30% relative humidity (RH) (ISOS-D1), damp heat exposure at 85 °C and 85% RH (ISOS-D3), and outdoor operational stability continuously monitoring device performance for 10 months under maximum power point tracking on a roof-top test site in Berlin, Germany (ISOS-O3). LAB encapsulation of perovskite devices consists of glue and a cover glass and can be performed at ambient temperature, in an inert environment without the need for complex equipment. This glue-based encapsulation procedure allowed PSCs to retain more than 93% of their conversion efficiency after 1566 h of storage in ambient atmosphere and, therefore, is sufficient and suitable as an interim encapsulation for cell transport or short-term experiments outside an inert atmosphere. However, this simple encapsulation does not pass the IEC 61215 damp heat test and hence results in a high probability of fast degradation of the cells under outdoor conditions. The COM encapsulation procedure requires the use of a vacuum laminator and the cells to be able to withstand a short period of air exposure and at least 20 min at elevated temperatures (in our case, 150 °C). This encapsulation method enabled the cells to pass the IEC 61215 damp heat test and even to retain over 95% of their initial efficiency after 1566 h in a damp heat chamber. Above all, passing the damp heat test for COM-encapsulated devices translates to devices fully retaining their initial efficiency for the full duration of the outdoor test (>10 months). To the best of the authors' knowledge, this is one of the longest outdoor stability demonstrations for PSCs published to date. We stress that both encapsulation approaches described in this work are useful for the scientific community as they fulfill different purposes: the COM for the realization of prototypes for long-term real-condition validation and, ultimately, commercialization of perovskite solar cells and the LAB procedure to enable testing and carrying out experiments on perovskite solar cells under noninert conditions.

Encapsulation and Stability Testing of Perovskite Solar Cells for Real Life Applications

With the progress in the development of perovskite solar cells, increased efforts have been devoted to enhancing their stability. With more devices being able to survive harsher stability testing conditions, such as damp heat or outdoor testing, there is increased interest in encapsulation techniques suitable for this type of tests, since both device architecture compatible with increased stability and effective encapsulation are necessary for those testing conditions. A variety of encapsulation techniques and materials have been reported to date for devices with different architectures and tested under different conditions. In this Perspective, we will discuss important factors affecting the encapsulation effectiveness and focus on the devices, which have been subjected to outdoor testing or damp heat testing. In addition to encapsulation requirements for these testing conditions, we will also discuss device requirements. Finally, we discuss possible methods for accelerating the testing of encapsulation and device stability and discuss the future outlook and important issues, which need to be addressed for further advancement of the stability of perovskite solar cells.

Investigation of Opto-Electronic Properties and Stability of Mixed-Cation Mixed-Halide Perovskite Materials with Machine-Learning Implementation

The feasibility of mixed-cation mixed-halogen perovskites of formula AxA’1−xPbXyX’zX”3−y−z is analyzed from the perspective of structural stability, opto-electronic properties and possible degradation mechanisms. Using density functional theory (DFT) calculations aided by machine-learning (ML) methods, the structurally stable compositions are further evaluated for the highest absorption and optimal stability. Here, the role of the halogen mixtures is demonstrated in tuning the contrasting trends of optical absorption and stability. Similarly, binary organic cation mixtures are found to significantly influence the degradation, while they have a lesser, but still visible effect on the opto-electronic properties. The combined framework of high-throughput calculations and ML techniques such as the linear regression methods, random forests and artificial neural networks offers the necessary grounds for an efficient exploration of multi-dimensional compositional spaces.