Aleksandra N. Zhivchikova

This study evaluates the effectiveness of parylene derivatives as encapsulation materials for enhancing the stability of perovskite solar cells (PSCs). The research compares four types of parylene (N, C, D, and F) based on their ability to protect perovskite films and prevent PSC degradation under high temperature and humidity conditions. Experimental results indicate that parylene-C offers superior barrier properties, effectively suppressing perovskite decomposition under prolonged illumination and elevated temperatures in an ambient environment. Parylene-N demonstrates exceptional performance in encapsulating complete PSCs, achieving dark ambient storage stability for more than 10 000 h with minimal efficiency losses (2%) during dark ambient storage. Despite superior water barrier properties, chlorine-containing parylene derivatives (C and D) are found to be unsuitable for solar cells with silver top electrodes due to silver ion diffusion, resulting in device failure. In contrast, fluorinated parylene-F avoids this issue but shows lower moisture resistance. The findings emphasize the importance of material compatibility and suggest that unsubstituted parylene-N is the best candidate for PSC encapsulation in the case of silver electrodes and relatively low air humidity (RH < 35%).

This study investigates a series of electron transport materials (ETMs) in wide-bandgap perovskite solar cells with the Cs0.17FA0.83Pb(I0.6Br0.4)3 photoactive layer. Power conversion efficiencies of up to 23.2% were achieved under an artificial light source (1000 lux, 6000 K LED) for the devices incorporating SnO2 passivated with fullerene derivative. However, the fullerene derivative induced rapid interfacial degradation. In contrast, solar cells utilizing SnO2 ETM passivated with amino-based compounds exhibited stable performance under continuous 1 Sun illumination during 2300 h in an inert atmosphere and under indoor lighting in ambient conditions. This was attributed to a reduced density of defects on the surface of the ETM and enhanced interfacial stability. These findings underscore the importance of the rational ETM selection for efficient and stable wide-bandgap perovskites.

There is a resurgence in the use of triphenylamine-based donor materials (TPA) in the field of perovskite photovoltaics. This work presents the synthesis of two novel conjugated small molecules (CSM's), TPA-t and TPA-t EH, which are functionalized with triisopropylsilyl groups and 2-ethylhexyl side chains. These molecules show promise as hole transport materials, which possess high hole mobilities of 1.5 × 10-4 and 2.9 × 10-3 cm2 V−1 s-1 due to self-organization. TPA-t and TPA-t EH possess HOMO energy levels at -5.38 and -5.31 eV, which is well-aligned with valence band of standard perovskite MAPbI3.This resulted in outstanding open-circuit voltages of 1100 and 1080 mV. TPA-based molecules were investigated as HTLs in n-i-p PSCs without additional doping and enabled high efficiency (17.4 %) same as for devices with state-of-the-art polytriarylamine (PTAA) HTL. The obtained results suggest that developed materials could potentially compete with PTAA when further material structure modification.

Hybrid organic–inorganic perovskite solar cells (PSCs) have drawn great attention in the past decade due to the rapid growth of their power conversion efficiency (PCE) and the advantage of their low-cost fabrication. The hole-transport materials (HTMs) play a crucial role in achieving high efficiency and operational stability of PSCs. In this work, we report the synthesis of two novel conjugated polymers by coupling of the alkylsilyl-substituted benzo[1,2-b:4,5-b′]dithiophene unit with the thiophene-bridged pyrazine block and their investigation as dopant-free HTMs in n–i–p PSCs. The devices with polymer PBPyT-ex (poly[(4,8-bis(5-(triisopropylsilyl)thiophen-2-yl)-2,6-benzo[1,2-b:4,5-b′]dithiophene)-alt-5,5′-(2,5-bis(4-(2-ethylhexyl)thiophen-2-yl)pyrazine)]) demonstrate PCEs up to 17.5%, outperforming the 14.9% efficiency of PSCs with PBPyT-in (poly[(4,8-bis(5-(triisopropylsilyl)thiophen-2-yl)-2,6-benzo[1,2-b:4,5-b′]dithiophene)-alt-5,5′-(2,5-bis(3-(2-ethylhexyl)thiophen-2-yl)pyrazine)]), which is attributed to the difference in the quality of HTM films. The results obtained feature the combination of pyrazine, thiophene and benzodithiophene units as a successful example of polymeric HTM backbone design for PSCs with encouraging efficiency and high operational stability over 1500 h under continuous illumination.

Here, we present a synthesis of three novel conjugated block-copolymers (BCP) with general formula P3HT-bridge-TBO, where P3HT is a poly(3-hexyl)thiophene, TBO is a thiophene-benzothiadiazole block, and the bridge is composed of two fluorene units (FF) or two thiophenes (TT) or a mixture (TF). It is demonstrated that the physicochemical properties of the materials with different bridges are similar. Furthermore, P3HT-bridge-TBO materials are investigated in PSCs with classical n-i-p configuration for the first time. PSCs with BCPs reach average efficiencies with a top of 14.4% for P3HT-FF-TBO. At the same time, devices demonstrate spectacular long-term operation stability after 1000 h under constant illumination with minor changes in efficiency, while PSCs with state-of-the-art hole-transport layer demonstrate unstable behavior. This groundbreaking work demonstrates the potential of BCP to ensure the stable operation of perovskite photovoltaics.

Donor-acceptor conjugated polymers are considered advanced semiconductor materials for the development of thin-film electronics. One of the most attractive families of polymeric semiconductors in terms of photovoltaic applications are benzodithiophene-based polymers owing to their highly tunable electronic and physicochemical properties, and readily scalable production. In this work, we report the synthesis of three novel push–pull benzodithiophene-based polymers with different side chains and their investigation as hole transport materials (HTM) in perovskite solar cells (PSCs). It is shown that polymer P3 that contains triisopropylsilyl side groups exhibits better film-forming ability that, along with high hole mobilities, results in increased characteristics of PSCs. Encouraging a power conversion efficiency (PCE) of 17.4% was achieved for P3-based PSCs that outperformed the efficiency of devices based on P1, P2, and benchmark PTAA polymer. These findings feature the great potential of benzodithiophene-based conjugated polymers as dopant-free HTMs for the fabrication of efficient perovskite solar cells.

Perovskite solar cells (PSCs) currently reach high efficiencies, while their insufficient stability remains an obstacle to their technological commercialization. The introduction of hole-transport materials (HTMs) into the device structure is a key approach for enhancing the efficiency and stability of devices. However, currently, the influence of the HTM structure or properties on the characteristics and operational stability of PSCs remains insufficiently studied. Herein, we present four novel push-pull small molecules, H1-4, with alternating thiophene and benzothiadiazole or fluorine-loaded benzothiadiazole units, which contain branched and linear alkyl chains in the different positions of terminal thiophenes to evaluate the impact of HTM structure on PSC performance. It is demonstrated that minor changes in the structure of HTMs significantly influence their behavior in thin films. In particular, H3 organizes into highly ordered lamellar structures in thin films, which proves to be crucial in boosting the efficiency and stability of PSCs. The presented results shed light on the crucial role of the HTM structure and the morphology of films in the performance of PSCs.

In the last decade, perovskite photovoltaics gained popularity as a potential rival for crystalline silicon solar cells, which provide comparable efficiency for lower fabrication costs. However, insufficient stability is still a bottleneck for technology commercialization. One of the key aspects for improving the stability of perovskite solar cells (PSCs) is encapsulating the photoactive material with the hole-transport layer (HTL) with low gas permeability. Recently, it was shown that the double HTL comprising organic and inorganic parts can perform the protective function. Herein, a systematic investigation and comparison of four double HTLs incorporating polytriarylamine and thermally evaporated transition metal oxides in the highest oxidation state are presented. In particular, it was shown that MoO_x, WO_x, and VO_x-based double HTLs provided stable performance of PSCs for 1250 h, while devices with NbO_x lost 30% of their initial efficiency after 1000 h. Additionally, the encapsulating properties of all four double HTLs were studied in trilayer stacks with HTL covering perovskite, and insignificant changes in the absorber composition were registered after 1000 h under illumination. Finally, it was demonstrated using ToF-SIMS that the double HTL prevented the migration of perovskite volatile components within the structure. Our findings pave the way towards improved PSC design that ensures their long-term operational stability.

Recent studies have shown that charge transport interlayers with low gas permeability can increase the operational lifetime of perovskite solar cells serving as a barrier for migration of volatile decomposition products from the photoactive layer. Herein we present a hybrid hole transport layer (HTL) comprised of p-type polytriarylamine (PTAA) polymer and vanadium(V) oxide (VO_x). Devices with PTAA/VO_x top HTL reach up to 20% efficiency and demonstrate negligible degradation after 4500 h of light soaking, whereas reference cells using PTAA/MoO_x as HTL lose ∼50% of their initial efficiency under the same aging conditions. It was shown that the main origin of the enhanced device stability lies in the higher tolerance of VO_x toward MAPbI₃ compared to the MoO_x interlayer, which tends to facilitate perovskite decomposition. Our results demonstrate that the application of PTAA/VO_x hybrid HTL enables long-term operational stability of perovskite solar cells, thus bringing them closer to commercial applications.