Developing Hole Selective Layers and Implementing Large-size Organic Cations for Perovskite Solar Cells

212 p.Thesis Abstract Organic-inorganic halide perovskite solar cells(PSCs) have emerged as one of the best candidates in next generation photovoltaics since their introduction in 2009. The power conversion efficiency (PCE) has dramatically increased from 3.8% to 25.7% in a decade. However, due to their limited device stability, the path to commercialization has been hindered, despite excellent PCEs. The highest performing PSCs is composed of several layers such as electron transport layers, an n-type mesoporous TiO2 layer, a perovskite layer, a hole transporting layer and a metal electrode. The high PCE can be achieved by effectively extracting and collecting the photo generated holes and selectively reducing the charge recombination loss. The state-of-art Spiro-OMeTAD is themost commonly used hole transporting material in the literature,however, its high cost due to multistep synthesis process, complex purification and instability caused by adding of hygroscopic p-typedopants, hinders the large-scale industrialization of PSCs. Thus, thedevelopment of new designed HTMs is highly desired.Additionally, the dimensionality of the perovskite influences the performance and stability of the PSCs. The reduction of dimensionality to produce lower-dimensional perovskites or analternative approach to implement an interfacial layer of the least amount of large organic cation to 3D perovskite surface to form bilayer or layered/3D mixed dimensional perovskites greatlyenhance the photovoltaic performance and stability of PSCs.Thus, the studies in this thesis aim to develop new hole-transporting materials that would be inexpensive and easily synthesizable andcan be effectively implemented for PSC applications. A series ofHTMs based on small molecules were designed and synthesized and investigated to understand the behaviour as a charge selective layerin PSCs, to further reduce the cost and improve the stability.Further more, the thesis discusses the work on the dimensionality of the perovskite and interface engineering of the perovskite absorber layer with large organic cations for improved performance and longterm stability purposes.Thus, the thesis aims to discuss the studies and investigations on themolecularly designed hole-transporting materials (HTMs) andemploy the large-size organic cation as an interface layer or dopingto form reduced mixed-dimensional perovskite absorber forenhancing the overall performance and long-term stability of thePSCs.Bcmaterials: Basque Center for Materials, applications & nanostructure

Molecular Interface Engineering via Triazatruxene-Based Moieties/NiOx as Hole-Selective Bilayers in Perovskite Solar Cells for Reliability

Interface engineering is an effective approach to decrease nonradiative recombination and the energy barrier at the perovskite/hole transporting layer (HTL) interfaces. To overcome such limitations, an organic semiconductor (DTT-EHDI 2) is proposed, which is, composed of dithienothiophene (DTT) as the core and a planar triazatruxene incorporating an alkyl chain as the side group. This is noted to be an effective interfacial layer for inverted planar perovskite solar cells (PSCs). The altered interface effectively minimizes the detrimental charge recombination and tailors the photoinduced charge transfer dynamics at the interface of the inorganic HTL/perovskite. The π-conjugation in DTT-EHDI 2 induces high hole mobility and electrical conductivity via electron-donating properties and strong π–π intermolecular interaction. The synergetic approach leads to a substantial performance enhancement in dopant-free DTT-EHDI 2-based inverted planar PSCs, achieving 18.15% power conversion efficiency with negligible hysteresis effect. The present approach provides an effective direction of the cost-effective thiophene derivative as an interfacial agent to escalate the optoelectronic performances in photovoltaics. © 2022 Wiley-VCH GmbHThis work received funding from the European Union H2020 Programme under a European Research Council Consolidator grant (MOLEMAT, 726360) and PARASOL (RTI2018-102292-B-I00) and ARISE (PID2019-111774RB-100) from the Spanish Ministry of Science and Innovation.Peer reviewe

Dibenzo-tetraphenyl diindeno perylene as hole transport layer for high-bandgap perovskite solar cells

Semi-transparent perovskite solar cells have the competitive edge of being employed for building integrated photovoltaics due to their esthetic benefits as light harvesting windows/facades. Perovskites have received considerable attention in recent years as a thin film photovoltaic alternative, that can also be tweaked for its transparency, evolving from potentially high bandgaps that are suited for semi-transparent solar cell fabrication. Due to the existing trade of between the efficiency and transparency of a perovskite solar cell, tuning the band gap can address this by making a bridge between the aforementioned parameters. We report our findings on the use of a wide-bandgap perovskite MAPbBr3, with a rational energetic level hole transport materials based on polycyclic aromatic hydrocarbon molecules that can be a promising alternative class of p-type material. In the present work, DBP (Dibenzo{[f,f′]-4,4′,7,7′-tetraphenyl}diindeno[1,2,3-cd :1′,2′,3′-lm]perylene was evaluated with high bandgap as well as with mixed (FAPbI3)0.85(MAPbBr3)0.15 perovskites for the fabrication of solar cell. DBP-based solar cells yielded competitive power conversion efficiencies as compared with classical HTMs.Peer reviewe

Aggregation-Induced and Polymorphism-Dependent Thermally Activated Delayed Fluorescence (TADF) Characteristics of an Oligothiophene: Applications in Time-Dependent Live Cell Multicolour Imaging

Typically, molecules with a twisted donor-acceptor (D-A) architecture have been exploited for constructing thermally activated delayed fluorescence (TADF) materials. Herein, we report the first example of a thiophene-based thermally activated delayed fluorescent molecule without a D-A architecture. Compound 1 (2,5-bis(2,2-di(thiophen-2-yl)vinyl)thiophene) is conformationally flexible and shows weak fluorescence in the solution state but displays bright TADFin both condensed and solid states. Compound 1 crystallized in two different polymorphs (1 a and 1 b). Interestingly, both polymorphs show distinctly different TADF features. The broad spectral features and the TADF characteristics of 1 have been explored for the time-dependent multicolor (green, yellow and red) imaging of living cells

Dibenzo-Tetraphenyl Diindeno as Hole Transport Layer for Perovskite Solar Cells Fabrication

Semi-transparent perovskite solar cells have the competitive edge of being employed for building integrated photovoltaics due to their aesthetic benefits as light harvesting windows / facades. Perovskites have received considerable attention in recent years as a thin film photovoltaic alternative, that can also be tweaked for its transparency, evolving from potentially high bandgaps that are suited for semi-transparent solar cell fabrication. Due to the existing trade of between the efficiency and transparency of a perovskite solar cell, tuning the band gap can address this by making a bridge between the aforementioned parameters. We report our findings on the use of a wide-bandgap perovskite MAPbBr3, with a rational energetic level hole transport materials based on polycyclic aromatic hydrocarbon molecules that can be a promising alternative class of p-type material. In the present work, DBP (Dibenzo{[f,f\u27 ]-4,4\u27,7,7\u27-tetraphenyl}diindeno[1,2,3-cd :1\u27,2\u27,3\u27-lm]perylene, was evaluated with high band gap as well as with (FAPbI3)0.85(MAPbBr3)0.15 perovskites for the fabrication of solar cell. DBP based solar cells yielded competitive power conversion efficiencies as compared to classical HTMs.</p