Synthesis and Studies of Dopant-Free Charge Transporting Materials Containing Acceptor Moieties for Inverted Perovskite Solar Cells

Dr. Viktorija Andruleviciene

Inverted perovskite solar cells (IPSCs) have been attracting increasing attention due to their high operational stability, negligible hysteresis, and cost-effective fabrication process. A maximum power conversion efficiency of 23.72% for IPCS is already achieved, however, the recent progresses in their performance suggest that IPSCs are still far from being fully optimized. Besides the perovskite absorber, the adjacent charge transport layers are also crucial for photovoltaic performance, as they ensure the transport and extraction of photogenerated holes and electrons. However, the design of new efficient organic charge transporting materials for IPSCs is a great challenge. The goal of the project is the development of dopant-free charge transport materials with acceptor moieties for IPSCs. The acceptor groups have been investigated as a successful approach to improve energy level alignment and charge mobility resulting in enhanced photovoltaic properties of IPSCs. The goal of the project requires joint efforts of the researchers having expertise in the synthesis of organic electroactive compounds as well as fabrication and characterization of IPSCs.

1. Development of commercially promising organic charge transporting materials with acceptor moieties

The low-cost synthesis of the organic charge transporting materials for IPSCs is of great importance. KTU researchers will focus on the simple and cost-effective synthesis methods for the materials containing donor and acceptor moieties. The acceptors with fluoro-, nitrogen -, oxygen- or cyano- containing substituents will be used to improve performance in IPCS. Oxygen and fluorine atoms can induce intra- and intermolecular interactions in molecules leading to the improvement of energy level alignment and the increase in charge extraction [J. Chem. Eng. 402 (2020) 125923]. Some cyano-substituted compounds have demonstrated an aggregation-induced effect leading to the high charge mobility in the solid state [ACS Appl. Energy Mater. 2021, 4, 6, 5756–5766].  Moreover, the acceptor substituents passivate defects in the perovskite layer improving the characteristics of the solar cells [J. Mater. Chem. A, 2020,8, 6517-6523].

2. Investigation of the newly synthesized organic charge transporting materials for IPCSs

JMU researchers will characterize and test the synthesized dopant-free organic semiconductors intended for IPSCs. This will be investigated by optical spectroscopy experiments to gain insight into the spectral features associated with the charge carriers. Using electron spin resonance (ESR), they will be able to determine the amount of the present localized and free charges in the dark and under illumination [Adv. Electron. Mater., 2022, 8, 2200113]. Using transient microwave conductivity (TRMS) charge carrier mobility and lifetime can be estimated [Adv. Energy. Mater., 2022, 12, 2102776]. The long-term stability of IPSCs is one of the critical issues that needs to be resolved for their commercial application. Removal of dopants from charge transporting layers has been shown to be very effective in the enhancement device stability [Chem Sci. 2019, 10(28), 6748–6769]. To assess this, JMU will investigate the capacitance of the device using either impedance measurements or transient open circuit voltage (OCVD) methods [Sust. Energy Fuels 2021, 5 3578-3587], which facilitate assigning ionic and free charge carrier properties in solar cells.

3. Raise the scientific potential of JMU and KTU transferring knowledge between researchers

Due to the interdisciplinary nature of the research planned in the project, there will be a transfer of knowledge between chemists and physicists. KTU researchers will transfer their knowledge in the design, synthesis, and investigation of organic charge transporting materials to JMU researchers. The collaboration with JMU researchers will provide knowledge to KTU researchers on the investigation of organic semiconductors and perovskite solar cells by the spin-sensitive magnetic resonance and transient conductivity methods. The sharing of knowledge between KTU and JMU will take place during online meetings, seminars, in the analysis of the results, and finally in the drafting of the manuscripts that will allow the preparation of a joint proposal under the Horizon Europe program. It is obvious that the close and focused cooperation between KTU and JMU will strengthen the scientific potential of researchers on both sides.

Direct target group is the implementers of the project. 4 team members from JMU and 6 team members from KTU will collaborate to achieve the goal of the project.

Indirect target group is 50 academic staff / faculty members, both from chemistry and physics, at JMU and KTU who will participate in the seminars and discussions. In addition, the indirect group will also include members of the research (organic and perovskite PV) community who will come to read the results published in international journals.