Project leader: Dr. Marcela Socol

Experienced researcher: Dr. Nicoleta Preda

Experienced researcher: Dr. Anca Stanculescu

Post-doctoral researcher: Dr. Oana Rasoga

Post-doctoral researcher: Dr. Andreea Costas

Post-doctoral researcher: Dr. Carmen Breazu

Doctoral student: Drd. Gabriela Baiasu

Experienced researcher: Dr. Stefan Antohe

The project is focused on the development of indium-free organic (OPV) and hybrid photovoltaic (HPV) cell structures on flat and nanopatterned multilayer transparent conductive electrode (MTCE) on rigid and flexible substrates. Thus, the expensive indium tin oxide (ITO), the most used transparent conductive electrode in the OPV/HPV cell structures, will be replaced by low-cost MTCE based on metallic oxide/ metal/ metallic oxide (ZnO/Ag(Au)/ZnO) films with lower thickness than the classical single layer ITO but with similar properties to this. In addition, low quantity of material will be used (compared to the silicon based systems) to prepare the active films (organic/inorganic nanostructures in organic) of the OPV/HPV cells. The inorganic nanostructures based on copper sulphides will be inserted in the organic matrix for improving the optical and electrical properties of the developed structures and also to increase their stability.  Patterned surfaces obtained by UV nanoimprint lithography will be involved in order to increase efficiently the light harvesting in the active layers and in this way enhancing the electrical parameters of the fabricated PV cells. The fabricated OPV/HPV devices within this project can be further used in niche applications (ex. small electronic devices, wearable electronics, etc.).

Stage 1/2025

The objective of the first stage was to obtain multilayer transparent conductive electrodes (MTCE) on different flat and patterned substrates, rigid and flexible, for their integration into organic and hybrid solar cell devices. Thus, deposition substrates were patterned by UV nanoimprint lithography (UV-NIL) in order to obtain ordered structures (patterns) with cylinder or cone geometry. Next, multilayer structures were obtained by successive deposition of dielectric/metal/dielectric films using radio frequency magnetron sputtering (RF-MS - in the case of dielectric and metal layers) and vacuum thermal evaporation (VTE - in the case of metal layers). In the same deposition cycle, MTCE structures were deposited on the substrates of interest (rigid flat, flexible flat, rigid patterned and flexible patterned) to evaluate the influence of deposition substrate type on the properties of the fabricated MTCEs. Thus, flat substrates as rigid glass (RG), flexible glass (FG), polyethylene terephthalate (PET) and polyethersulfone (PES) and patterned substrates as patterned rigid glass (glass-NP), patterned polyethylene terephthalate (PET-NP) and patterned polyethersulfone (PES-NP) were used in the deposition of ZnO/Ag/ZnO and ZnO/Au/ZnO MTCE. In the preparation of MTCE the following parameters were varied: (i) metal film deposition method (VTE or MS), (ii) ZnO film thickness (100 nm, 60 nm, 30 nm, 25 nm or 20 nm), (iii) metal type (Au or Ag), (iv) Au metal layer thickness (10 nm or 7 nm). The fabricated MTCEs were characterized from morphologically, structurally, optically and electrically point of view. From these measurements the key parameters such as the roughness parameter (RMS), transmittance at 550 nm wavelength (T₅₅₀) and electrical parameters (electrical resistivity - ρ and surface resistance - Rs), relevant for the subsequent integration of the MTCEs into solar cell devices, were determined. In the case of MTCE deposited on flat substrates, the results can be summarized as follows: (i) ZnO/Ag/ZnO structures with thicknesses (nm) of 100/6/60 and 6/6/60 nm deposited by MS/VTE/MS - the best properties (RMS = 2.3 nm, T₅₅₀ = 82.7 % and Rs = 9.5 Ω/sq) obtained for the structure made on FG; (ii) ZnO/Au(Ag)/ZnO structures with thicknesses (nm) of 30/6/30 deposited by MS/VTE/MS - the best properties (T₅₅₀ = 82.4 % and Rs = 19.3 Ω/sq) obtained for the ZnO/Au/ZnO structure made on FG; (iii) ZnO/Au(Ag)/ZnO structures with thicknesses (nm) of 20/7/25 deposited by MS - the best properties (RMS ~3-5 nm, T₅₅₀ ~80-82 % and Rs ~13-17 Ω/sq) obtained for all ZnO/Au/ZnO structures made on RG, FG and PET; (iv) ZnO/Au/ZnO structures with thicknesses (nm) of 20/7/20 and 20/10/20 deposited by MS/VTE/MS - the best properties (RMS = 2.4 nm, T₅₅₀ = 81.9 % and Rs = 5.7 Ω/sq) and (RMS = 4.7 nm, T₅₅₀ = 80 % and Rs = 12.7 Ω/sq) obtained for ZnO/Au(10)/Zn structures made on FG and RG, respectively. In the case of MTCEs deposited on patterned substrates, the best values ​​for surface resistance (Rs) were obtained for: (i) ZnO(20)/Au(7)/ZnO(25) structures deposited by MS on PES-NP substrate (Rs = 15.9 Ω/sq); (ii) ZnO(20)/Au(10)/ZnO(20) structures deposited by MS/VTE/MS on PET-NP substrate (Rs = 9.7 Ω/sq) and glass-NP substrate (Rs = 9.2 Ω/sq). Thus, MTCEs with properties (roughness, transmittance and surface resistance) suitable for integration into solar cell devices were fabricated on flat and patterned rigid and flexible substrates.

1. M. Socol,  N. Preda, A. Costas, G. Petre, A. Stanculescu, I. Stavarache, G. Popescu-Pelin,  S. Iftimie, A. Stochioiu,· A. M. Catargiu, G. Socol, Influence of flexible substrate nature covered with ITO on the characteristics of organic heterostructures fabricated by laser deposition techniques, Applied Physics A 131,17, 2025.

2. Marcela Socol, Nicoleta Preda, Andreea Costas, Gianina Popescu-Pelin, Sorina Iftimie Gabriela Petre, Andrei Stochioiu, Ana Maria Catargiu, Gabriel Socol, and Anca Stanculescu, Composite films based on poly(3-hexylthiophene):perylene diimide derivative:copper sulfide nanoparticles deposited by matrix assisted pulsed laser evaporation on flexible substrates for photovoltaic applications, Journal of Composites Science 9, 172, 2025.

1. M. Socol, N. Preda, G. Petre, S. Iftimie. A. Stochioiu, G. Popescu-Pelin, A.M. Catargiu, G. Socol, A. Costas, A. Stanculescu, Flexible substrates coated with hybrid thin films by MAPLE for optoelectronic applications,  NanoSeries2025, 16-20 June 2025, Valencia, Spain.

2. Marcela Socol, Nicoleta Preda, Carmen Breazu, Ionel Stavarache, Gabriela Petre, Andreea Costas, Anca Stanculescu, Effect of deposition substrate on the properties of oxide/metal/oxide multilayer transparent conductive electrodes, 23th International Balkan Workshop on Applied Physics and Materials Science, 09-12 July 2025, Constanta, Romania.

3. M. Socol, N. Preda, C. Breazu, O. Rasoga, I. Stavarache, G. Petre, A. Costas, A. Stanculescu, Deposition of oxide/metal/oxide transparent conductive electrodes with tailored properties on flexible substrates, 15th International Conference & Exhibition on Green Flexible Printed Electronics Industry (ICEFPE25), 17-19 November 2025, Athens, Greece.