Periodic Reporting for period 4 - HY-NANO (HYbrid NANOstructured multi-functional interfaces for stable, efficient and eco-friendly photovoltaic devices)
Okres sprawozdawczy: 2024-01-01 do 2024-06-30
The planned objectives of the project have been successfully achieved, in line with what proposed in the Work packages and described in the DoA. For each of the objectives, significant advances have been made. In particular:
-WP1) aiming at exploring new cations and new 2D perovskites to stabilize the perovskite crystal structure and to optimize the optoelectronic properties and bandgap. We have designed novel 2D perovskite materials including fluorinated ones (T1.1) and we evaluated their optical properties (T1.3) and stability (T1.4) [see publications n. 11, 12 and 13]. In addition, we have explored new 2D perovskites and revealed their incredible tunability in terms of material band gap, by simple halide substitution, also revealing a nanoscale phase segregation happening behind this class of materials, which can be adopted for solar cells but also extended into novel high impact optoelectronic applications such as light emitting devices [see Zanetta et al. Adv. Mater. 2022, 34, 2105942]. Moreover, the tunability of 2D perovskite has been pushed to the extreme, manipulating the structural arrangement of the inorganic chain and their directional growth, leading to a new fundamental understanding on the crystallization mechanism behind 2D growth (publication submitted and patent pending). In addition, we screened lead-free perovskite (T1.2) [See publications n. 14 and Pisanu et al. J. Mater. Chem. A, 2020, 8, 1875, n 24] and we developed new lead-free perovskites in the form of Silver/Bismuth Double Perovskites where we found un unprecedented physical behavior, which contrasts with Pb-based perovskites, with a dominant excitonic effects. The large Stokes shift observed is explained by the inherent soft character of the double-perovskite lattices, rather than by the often-invoked band to band indirect recombination [see Pantaler et al. JACS Au 2022, 2, 136]. In addition, the group have deeply investigated the issues derived to the use of toxic elements, resulted in two publications upon invitation [see publications n. 6 and 8] (WP2). Photophysical studies (T1.3) revealed the exception physics behind the layered structure, such as the Stark Effect unveiled for the first time [see publication n. 9]. In addition, the team has also developed a unique set-up for the detection of Photoluminescence signal, its decays (with ps resolution) and its quantum yield (PLQY, essential to test a good working material with minimal radiative recombination). The results appeared in [Pica et al. Struct. Dyn. 2022, 9, 011101, publication n 22], which demonstrated the combined skills of the HY-NANO team and the exploitation of my previous expertise in optical spectroscopy, now transferred to the group. In addition, the team contributed in understanding the fundamental exciton polariton characteristics of such materials (see publication n. 30). Regarding material stability (T.1.4) specific work has been conducted on material characterization by means of combined techniques such as PLQY and Absorption upon aging, X-Ray Diffraction of the fresh and aged materials, combined with full device characterization that enables a clear understanding on the degradation paths under thermal stress [See publication n. 4]. Additionally, we have also contributed to the understanding behind the photostability of 2D and quasi2D perovskites and we identified a critical oxygen concentration in the surrounding environment that affects the mechanism and strongly enhances the rate of layered perovskite photodegradation [see Udalova et al. ACS Applied Materials & Interfaces 2022, 14, 961]. Based on the work here investigated, as reference material, the 3D perovskite has been optimized (T.1.5) serving as a material control, which is also used for our reference device (WP2). We used the material developed in WP1 for the development of the 2D/3D stack interfaces (T2.1) along with the characterization of the photophysical processes therein (T2.2) [see publications n. 10 and 15]. The material characterization discussed in WP1 also applies to the interfaces, for which the understanding of photophysical processes and interfacial losses is crucial [see Pica et al. Struct. Dyn. 2022, 9, 011101] (WP3). Also, different stability tests have been carried out on the materials and interfaced developed, which manifest directly in highly performing devices, as shown by the results in WP3. The interface developed in WP2 have been used for the realization of perovskite solar cells, with a special focus at the beginning on carbon-based perovskite solar cells [see publications n. 4 and 7, at later stage also on nip perovskite solar cells as well as pin solar cells. In particular, we studied the long-term evolution of the interface (T2.3). We revealed that the small cation for the 3D layer can migrate to the 2D top layer and altering its structure over time. By playing with the 2D perovskite material, we show that this migration can be blocked improving the cell lifetime. Such findings provide a deep understanding and delineate precise guidelines for the smart design of multidimensional perovskite interfaces for advanced PVs [see publication n. 15]. The understanding on the interface stability is crucial for the device operation, as well as the response of the material under accelerated thermal stress [see publication n. 10].
- WP3.) Device fabrication, development and optimization has been the core of the HY-NANO project. Considering the current state of the art for the development of both nip and pin perovskite solar cells, our strategy has been to implement and fabricate both standard (nip) perovskite solar cells, using a metal oxide as electron transporting material (ETM) and spiroOMeTAD as hole transporting material (HTM) as well as inverted (pin) devices where the perovskite is interfaced between a polymeric (HTM) and fullerene layer (as ETM). Upon building the lab facility from scratch, we first dedicated to nip solar cells (counting on my previous experience in the field). Upon two years of intense optimization, the team was able to fabricate efficient and reproducible solar cells with power conversion efficiency (PCE) around 22% for triple cation based solar cells and approaching 25% for FAPbI3 based devices [under review] fulfilling (T3.1) and the final ambitious goal of the project. More in details, the project results demonstrate concomitant boost of device efficiency and stability [see publications 26, 31 and 33] obtained by a careful optimization of the device interfaces (i.e. by introducing atomically thin graphene flake to boost electron transport and charge carrier injection) and by the implementation of new 2D cation both in the bulk and on the surface of the 3D perovskite. A careful understanding of the role of the 2D in passivating both bulk and surface defects allows for pushing device open circuit voltage while simultaneously improving the device stability [see in particular papers n.31 32 and 33]. Full device characterization (T.3.2) has been essential for the rational optimization of the device. Within these tasks, in particular, working on nip devices, we have developed novel quasi-2D perovskite interfaces (WP2) and devices, along with their full characterization. Such work revealed extremely interesting performances using only Quasi-2D (with high n) perovskites [see publication n. 7], demonstrating their high impact as active layer in working devices. In addition, we have also been working on all inorganic solar cells, using Cs instead of the organic compound, which can be an interesting alternative for a more stable solution (despite critical issues in terms of material processing, such as solubility). A review has been published on this topic [see publication n. 3]. Specific effort on device interface characterization (T.3.2) has been the focus of publication n. 16. In this work we studied in depth the interfacial recombination and we discovered the multiple roles of the 2D/3D interface in reducing interface recombination and charge accumulation by forming a local pn junction, which serves as ideal heterojunction for charge separation, reducing their recombination yield. This work has been considered a milestone in the understanding of the interface, as highlighted in E. von Hauff Chem 2021, 7, 1694. In parallel, we have also developed pin solar cells, contributing to analyzing how interface functionalization impacts on both nip and pin structure [see publication n. 5, 31 and 33] and, more specifically, working on pin device optimization. To this regard, the team has worked a lot on the optimization of 2D-cation interfaces inventing a double approach for both perovskite/HTM and perovskite/ETM optimization using strategic steps to incorporate large organic cations at those interfaces. This optimization resulted in the realization of pin devices with efficiency in the best case of 23.7%, setting the new world record for pin device [see publication n. 1]. This result has been highlighted in international press, being of recognized world-level impact for the very high proved PCE. Such work certainly demonstrated the importance of interface engineering (WP2) and paves the way for a new route in pin device realization. Finally, it is also worth mentioning that for our expertise, we have been invited to contribute to a very deep and wide review on current advances in new generation PVs, recently published in [see publication n. 2]. In addition, very recently, I lead a comprehensive article reviewing all the 2D perovskite interface methods and advances, I published in Nature Energy in 2024 (see publication 34). On the other side, specifically on stability, my team has worked on multiple direction, looking at self-healing properties of perovskite materials [see publication n32], as well as evaluating the critical conditions to really have a stable device: the outdoor operation. Indeed, in parallel to lab-aging characterization, we set a 40 days long experiment monitoring the real operation and power output of a nip perovskite solar cell (with efficiency close to 25%). Results (subject of submitted publication) revealed minimal losses in performances for such a prolonged period of measurements under harsh outdoor conditions. This sets a milestone in the field and a proof of concept of the technological relevance of the results produced in the frame of the HYNANO project. Such high stability has been obtained also thanks to the work done by my research team on new encapsulant materials, as goal of WP4.
-WP4.) The team has developed MOF based materials which have been used as nanoparticles embedded in polymeric coatings. Such coatings have been deposited on top – as wide sealing material- of highly efficient perovskite solar cells, showing a remarkable increase in the device stability (publication submitted). In addition, those MOF have been fully characterized, offering the promise for their application beyond photovoltaics (see publications n.19).
Beyond the work done in accordance to HYNANO WP, my team has also contributed in analyzing the cost, in terms of environmental impact and LCOE analysis of the produced technology, which resulted in a high impact publications (n. 27 and 29). This analysis is crucial for a real understanding on the potential of perovskite solar cell (from material design to device recycling) to enter in the near future solar market.
In relationship to the project objectives, the team has demonstrated a significant scientific advances in the field of hybrid perovskites, as testified by the awards obtained by the PI (such as the J. Mater. Chemistry Lectureship 2020) and the team member recognition (best Oral presentation at EMRS congress for Phd student Zanetta), the large number of invited lectures, the participation at international conferences as well as in the communications (see the dedicated website https://pvsquared2.unipv.it(odnośnik otworzy się w nowym oknie) and the communication appeared at National Newspapers and International Web-press released (as detailed below).