Transparent N- and Nb- Doped NiO-Based Heterostructures for Transparent and Tandem Solar Cells.
C. Aivalioti, A. Papadakis, E. Manidakis, E.I. Spanakis, M. Androulidaki, M. Kayambaki, K. Tsagaraki, A. Kostopoulos, C.C. Stoumpos, N.T. Pelekanos, M. Modreanu, E. Aperathitis, G. Craciun, C. Romanitan
New Materials and Concepts for Photovoltaic Devices
||New Materials and Concepts for Cells and Modules
||38th European Photovoltaic Solar Energy Conference and Exhibition
Buildings, in which humans are spending 85-90% of their life, are responsible for consuming about 40% of the total
produced energy and emitting 30% of the total CO2 in the atmosphere, while windows are responsible for the loss of
10-25% of the thermal energy of buildings. “Smart” windows can control and modulate solar heat and lighting and, it
is possible, at the same time to produce electricity. Furthermore, it is becoming apparent that for the future of our
Information & Telecommunication Societies there is a need for devices, which are based on environmentally friendly
materials and processes, for producing, handling and storing energy. Energy harvesting from ambient sources will
enable to power the Internet of Things (IoT) Systems like transparent, flexible, wearable electronics, etc.
The emerging class of oxide semiconductors and particularly wide gap oxides, can be fabricated as transparent solar
cells, harvesting UV solar radiation, and integrated into (opto-) electronics as power producers. Thus, transparent
solar cells can be used for energy autonomous smart windows like electrochromics as well as IoT systems.
In this presentation, metal oxides-based solar cells, namely p-NiO/n-TiO2, have been fabricated for transparent
applications. Undoped NiO and Nitrogen (N) or Niobium (Nb) single or co-doped NiO were fabricated by rf sputtering
by employing Ni and Ni-Nb targets in plasma containing %(Ar-O2-N2) gases. Compact and meso-porous TiO2 films
were fabricated by spin coating, on FTO-covered glass substrates followed by thermal treatment at 500°C for 15min
in air, which is the standard procedure used when these layers are to be used as electron transfer layers for
perovskites PVs. The TiO2/FTO/glass configuration was the substrate used for forming the NiO:N-Nb/TiO2
heterostructures. The oxide layers were characterized by AFM, XRD, SEM-EDX, Hall-effect and UV-Vis-NIR
spectroscopy whereas the photovoltaic behaviour of all-inorganic PSCs were characterized by dark and photo I-V, PL,
The N-doped NiO films were fabricated by gradually substituting O2 with N2 in plasma (0%-40% N2). The NiO:N film
with the optimum properties, fabricated in 50% Ar and equal amounts of O2 and N2 in plasma, was more transparent
(around 65%), had wider band gap (3.67eV), showed clear evidence of indirect band gap, 2.72eV and exhibited
narrower Urbach tail states, when compared to the undoped NiO. Preliminary results have revealed the
photosensitivity of the NiO:N films. The hybrid NiO:N/TiO2 heterojunction was transparent showing good output
characteristics, which were further improved upon thermal treatment. Experiments are in progress for incorporating
Nb in the Ni-O structure and obtaining oxide layers with improved and controllable electrical properties so the
transparent NiO/TiO2 heterostructure solar cell to be tested under AM1 illumination.