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.

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.

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.

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.

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.