A series of (BDD-X)n conjugated polymers, comprised of 5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c ']dithiophene-4,8-dione (BDD) and X = B (P1), X = TBT (P2), and X = TBTBT (P3), where T = thiophene and B = benzo[c][1,2,5]thiadiazole, have been synthesized and applied as dopant-free hole-transport layer materials in perovskite solar cells (PSCs). We explored the effect of the molecular structure of the block X on the optical and electronic properties of the polymers, the nanoscale morphology of their films, and the impact of all these parameters on the performance of the polymers in PSCs. As a result, using the polymer P1 with the simplest molecular architecture provided a power conversion efficiency (PCE) of 20.1% in solar cells, thus outperforming devices assembled with the more sophisticated polymers P2-P3 or the reference poly(triarylamine)-based hole-transport materials. The enhanced device performance is attributed to a better HOMO alignment of P1 with respect to the perovskite valence band, a low concentration of defects and suppressed carrier recombination at the P1/perovskite interface and, most importantly, a highly uniform film structure, as revealed by atomic force microscopy and infrared scattering near-field optical microscopy (IR s-SNOM) techniques. The supramolecular interactions of the building blocks of polymers P1-P3 with the perovskite films, resulting in the passivation of surface defects, were further studied by density functional theory calculations.

Novel polymers composed of thiophene units combined with non-fluorinated and fluorinated 2,1,3-benzothiadiazole units were synthesized and investigated as hole transport materials in perovskite solar cells. The impact of backbone fluorination on the optical and electronic properties of the resulting materials as well as the nanoscale morphology of their films deposited on the perovskite absorber layer was elucidated. The fluorinated polymer provided a superior power conversion efficiency of 18.6% coupled with high open-circuit voltage (VOC = 1.047 V)and short-circuit current (JSC= 23.4 mA cm-2).

Copolymers including carbazole-substituted naphtho-and quinoxalinedithiophene blocks, along with benzothiadiazole and thiophene, have been synthesized and systematically evaluated as dopant-free hole transport materials (HTMs) for perovskite solar cells. Polymers with optimal HOMO alignment relative to the perovskite valence band, suppressed carrier recombination at polymer/perovskite interface and, crucially, those forming the most uniform films, as confirmed by AFM and s-SNOM IR microscopy demonstrated enhanced device performance. These results provide valuable insights into the relationships between molecular structure, material properties, and device efficiency, offering guidance for the design of dopant-free polymeric HTMs for highperformance perovskite solar cells.

Two novel conjugated polymers comprised of 2,3-R2-di- thieno[3,2-f:2’,3’-h]quinoxaline, where R is 3’-(octyloxy)- phenyl (P1) or 2’-(2-ethylhexyl)thiophen-4’-yl (P2), and 2,1,3-benzothiadiazole have been synthesized using the Stille cross-coupling reaction. The synthesized polymers were investigated as hole transport layer (HTL) materials in perovskite solar cells. Polymer P2 as an HTL material provided improved short-circuit current and open-circuit voltage and, correspondingly, enhanced power conversion efficiency of perovskite solar cells compared to that of polymer P1.

A series of new homo- and copolymers P1-P6 with the main chains comprised exclusively of benzo [1,2-b:4,5-b'] dithiophene units were synthesized using Stille polycondensation reaction. The optical and electrochemical properties of P1-P6 polymers were studied to estimate the frontier orbitals energies and the Eg values. The obtained data demonstrate the possibility of controlling the electronic properties of polybenzo [1,2-b:4,5-b'] dithiophenes by varying only the structure and combinations of solubilizing alkyl side chains. The polymers P1-P6 were evaluated as hole transport materials in n-i-p perovskite solar cells. The highest efficiency of 18.6 % was delivered by the cells with one of the designed polymers with an optimal combination of alternating monoand dialkylthiophene substituents. The high photovoltaic performance and decent operational stability were achieved using polymer films without any doping, which paves a way to design of inexpensive and scalable dopant-free materials for perovskite solar cells.

Two new compounds BT-PDI and BT2-PDI2 were synthesized by the Sonogashira reaction between 4,7-diethynyl-2,1,3- benzothiadiazole and bromoperylene diimide derivatives. The HOMO and LUMO energy levels estimated by UV-VIS spectroscopy and cyclic voltammetry were –5.66/–3.75 and –5.33/–3.41 eV for the BT-PDI and BT2-PDI2, respectively; both compounds form high-quality and smooth coatings on the perovskite surface with the root mean square roughness values 5.95 and 7.80 nm for the BT-PDI and BT2-PDI2 films, respectively; the electron mobilities in the solid films estimated by photo-CELIV method are equal to 5.0 × 10–5 and 3.0 × 10–5 cm2 V–1 s–1, respectively. Both compounds being tested as electron transport layers in perovskite solar cells showed efficiency values of 14.44 and 13.01% for BT-PDI and BT2-PDI2, respectively.

A systematic study of the UV light-induced degradation of a series of structurally similar conjugated polymers revealed important relationships between the molecular structure of the used building blocks and photostability of the resulting materials. These findings form a set of important guidelines for future rational design of new absorber materials for efficient and stable organic solar cells.

A series of new homo- and copolymers P1–P6 with the main chains comprised exclusively of benzo[1,2-b:4,5-b']dithiophene units were synthesized using Stille polycondensation reaction. The optical and electrochemical properties of P1–P6 polymers were studied to estimate the frontier orbitals energies and the Eg values. The obtained data demonstrate the possibility of controlling the electronic properties of polybenzo[1,2-b:4,5-b']dithiophenes by varying only the structure and combinations of solubilizing alkyl side chains. The polymers P1–P6 were evaluated as hole transport materials in n-i-p perovskite solar cells. The highest efficiency of 18.6% was delivered by the cells with one of the designed polymers with an optimal combination of alternating mono- and dialkylthiophene substituents. The high photovoltaic performance and decent operational stability were achieved using polymer films without any doping, which paves a way to design of inexpensive and scalable dopant-free materials for perovskite solar cells.

First ferrocene- and ruthenocene-based nickel pincer complexes, NiCl[2,5-(But2PCH2)2C5H2Fe(C5H5)] (3a) and NiCl[2,5-(But2PCH2)2C5H2Ru(C5H5)] (3b), respectively, were synthesized and characterized by 1H, 31P1H, and 13C1H NMR spectroscopy. The structure of complex 3b was established by single-crystal X-ray diffraction.

In organic-inorganic perovskite solar cells (PSCs), the electron transport layer (ETL) plays a crucial role providing efficient electron extraction and transport required for achieving high device performance. Compared to traditional fullerene-based electron-transport materials (ETMs), non-fullerene small molecules have attracted much attention due to their tunable optoelectronic properties, lower cost, and much higher stability. In this work, we synthesized and characterized four perylenediimide (PDI) derivatives and investigated their optoelectronic properties in the context of application as ETMs for PSCs. To establish the compatibility of PDI films with perovskite absorber material, the surface properties of Cs0.12FA0.88PbI3/PDI bilayer stacks were studied using contact angle and infrared scattering scanning near-field microscopy methods. A study of the photochemical stability of these bilayer stacks showed that coating the perovskite film with a layer of PDI improves its tolerance with respect to light. Utilizing these molecules as ETMs in the inverted p-i-n PSCs delivered light power conversion efficiencies ranging from 11.1% to 15.4%, thus indicating the considerable effect of the PDI derivative molecular structure on the photovoltaic properties. Further development of this research direction may lead to the rational design of advanced PDI-based electron transport materials for efficient and stable PSCs.

Perovskite solar cells (PSCs) represent a promising next-generation photovoltaic technology considering their high efficiency and low cost. At the current stage, resolving the stability bottleneck is extremely urgent to realize PSCs' commercialization since the efficiencies of these cells are improved to a level comparable to that of crystalline silicon solar cells. Similar to other functional layers, a proper choice of the rear electrode atop the perovskite layer is equally important for achieving the device's long-term stability. This topic has not been comprehensively reviewed before. Here, recent progress in the development of rear electrodes based on metals, carbon-based materials, transparent conductive oxides, and conductive polymers is summarized, especially focusing on their different impacts on the device's long-term stability and associated degradation mechanisms. In the context of practical applications, the impacts of rear electrode materials on the device's overall efficiency and cost-effectiveness are also discussed.

Two new non-fullerene acceptors based on perylene diimide with acetylenic bridges were designed and synthesized employing Stille and Sonogashira coupling reactions as the key steps. Their optical and electronic properties were explored by UV–VIS spectroscopy and cyclic voltammetry, and energies of frontier molecular orbitals were estimated. Their preliminary studies in perovskite solar cells as electron transport materials showed the best power conversion efficiency for photocells of 14.18% value.

A series of four new oligomeric derivatives of NFA, NFA(S), NFA(Se) and NFA(N) with terminal perylene diimide groups modified with heteroatoms of S, Se, and N, were successfully synthesized and fully characterized by a variety of physicochemical methods. Due to deep LUMO levels, all compounds have an electron-acceptor character, which allows them to perform as electron transport compounds in perovskite solar cells of p-i-n architecture. The highest efficiency of 17.23 % was delivered by the solar cells with NFA(Se) electron transporting layer.

New small molecule photovoltaic materials containing benzimidazole fragment were prepared by cross-coupling of the corresponding 1-bromo-4-(imidazol-2-yl)benzenes with multiborylated/stannylated polycyclic (het)arenes. Energies of HOMO/LUMO levels were calculated from cyclic voltammetry and UV/VIS spectroscopy data and are within the ranges –5.27... –5.73 and –2.33...–2.89 eV, respectively. Solar cells based on three different perovskites as light absorbing layers and compound SM7 as electron transporting material demonstrated power conversion efficiency values up to 10.78% without doping additives or perovskite engineering.

A new acceptor unit anthra[1,2-b: 4,3-b': 6,7-c'']trithiophene-8,12-dione (А3Т) (A2) is synthesized and used to design D-A1 -D-A2 medium bandgap donor copolymers with same thiophene (D) and A2 units but different A1, i.e., fluorinated benzothiadiazole (F-BTz) and benzothiadiazole (BTz) denoted as P130 and P131, respectively. Their detailed optical and electrochemical properties are examined. The copolymers show good solubility in common organic solvents, broad absorption in the visible spectral region from 300 to 700 nm, and deeper HOMO levels of -5.45 and -5.34 eV for P130 and P131, respectively. Finally, an optimized polymer solar cell (PSC) based on P131 as the donor and narrow bandgap non-fullerene small molecule acceptor Y6 demonstrated a power conversion efficiency (PCE) of >11.13%. To further improve the efficiency of the non-fullerene PSC, the P130 is optimized by introducing a fluorine atom into the BTz unit, F-BTz acceptor unit, and PCE PSC based on P130: Y6 active layer increased to >15.28%, which is higher than that for the non-fluorinated analog P131:Y6. The increase in the PCE for former PSC is attributed to the more crystalline nature and compact π-π stacking distance, leading to more balanced charge transport and reduced charge recombination. These remarkable results demonstrate that A3T-based copolymer P130 with F-BTz as the second acceptor is a promising donor material for high-performance PSCs.

New conjugated (BDT-TTBTBTT) n copolymers are featured as promising hole-transport materials for n–i–p perovskite solar cells delivering efficiencies of up to ∼19%.

We have achieved a power conversion efficiency of 16.44% for the ternary polymer solar cell using a wide bandgap copolymer and two non-fullerene acceptors.

Three new donor-acceptor conjugated polymers incorporating same dithieno [2,3-e;3 ' 2 '-g]isoindole-7,9 (8H) (DTID) as medium acceptor and different donors, i.e., dithienosilole (DTS) PDTID-DTS (P1), dithieno-benzene (DTB) PDTID-DTB (P2) and dibenzothiophene (BDT) PDTID-BDT (P3) as a donor have been synthesized and explored for non-fullerene based BHJ polymer solar cells (PSCs). These copolymers had optical band gaps of 1.83-2.07 eV and HOMO energy levels of -5.37 to -5.67 eV. The P2 consists of a DTB donor unit that results in a deeper HOMO level of -5.67 eV, which may be due to the weak electron-donating nature of DTB. Pairing with the narrow bandgap non-fullerene acceptor BThIND-Cl, the P1, P2, and P3-based PSCs showed overall power conversion efficiency of 14.76 %, 7.22 % and 13.13 %, respectively. The PSCs based on P2 and P1 showed the highest and lowest values of open-circuit voltage, respectively, consistent with their HOMO energy levels. The lowest value of PCE for P2 may be associated with the negative HOMO offset between the P2 and BThIND-Cl, which hamper the hole transfer from the HOMO of BThIND-Cl to P2, resulting in a low value of short circuit current and fill factor. The higher value of PCE of 14.76 % for P1 may be related to the broader absorption profile of the active layer and balanced charge transport, more appropriate nanoscale phase separation, and compact 7C-7C stacking distance, leading to the high value of short circuit current and fill factor.

Developing efficient wide-bandgap copolymer donor materials to match with narrow bandgap non-fullerene acceptors is continuously ongoing for polymer solar cells. Herein, two new D-A copolymers are designed and synthesized by embedding the same anthra[1,2-b:4,3-b':6,7-c"] trithiophene-8,12-dione (A3T) acceptor unit and different donor units, i.e., BDTTZ (P126) and BDTTh (P127). These copolymers showed broad absorption from 350 to 680 nm and deeper HOMO energy level. We have used these two copolymers as donors and a narrow bandgap non-fullerene acceptor Y6 to prepare bulk heterojunction polymer solar cells (PSCs). After the optimization, P126:Y6 and P127:Y6 attained overall power conversion efficiency of 15.07% and 12.27%, respectively. The higher PCE for the P126 than P127 is associated with the more efficient photon harvesting and photogenerated excitons, balanced charge transport, and low energy loss. Our results may help to design new polymers with a deeper highest occupied molecular orbital level that will be well-matched with non-fullerene acceptors.

The development of conjugated polymers with wide absorption spectra is imperative to achieve high efficiency in polymer solar cells (PSCs), since most of these polymers usually absorb only a limited range of the solar spectrum. Random terpolymers consisting of three blocks (one electron-donor and two electron-acceptor blocks) are promising p-type polymers for PSCs, because the inclusion of a third block in the polymer macromolecules provides a synergistic effect of physical properties, such as absorption capacity, charge transfer, HOMO/LUMO energy levels, and photovoltaic characteristics. In this regard, we have developed and synthesized random terpolymers consisting of two different chromophores (DPP and BFCTP) with complementary absorption spectra as co-acceptor blocks in conjugated donor–acceptor (D–A) copolymers. Random copolymers exhibit both broad absorption and low HOMO levels favoring short-circuit current and idle voltage in PSCs. It is expected that new terpolymers consisting of one electron-donor unit and two electron-acceptor moieties will make a significant contribution to the development of highly efficient PSCs. It is expected that new ternary copolymers consisting of one electron-donor unit and two electron-acceptor fragments will make a significant contribution to the development of high-performance PSСs.