Axis 1: Prospective concepts for ultimate conversion efficiencies

Axis 1Elegant device concepts have emerged in the past years. They enable similar efficiencies as multijunctions in principle but with a much simpler electrical and optical design. Both concepts, hot carriers solar cells and intermediate bands solar cells are currently being thoroughly investigated by both IRDEP/IPVF, C2N and RCAST‐UT.

Here the focus is to realize proof of concept devices as at the moment none has been made with performances close to multi‐junction devices. They are expected to perform best under very high solar concentration first. The research program includes improved design of devices, search of efficient III‐V and development of adapted growth processes, and device concepts adaptation for very high concentration.

As was found in the first 4 years of the LIA, implementation of photonics is essential to achieve the full potential of these concepts. New III‐V materials, based on the dilute nitrides and bismides, and especially GaAsBiN alloy‐based for Intermediate Band structures and for integrated PV and thermoelectric conversion, will be studied. Materials and devices (Intermediate Band, Hot carriers, Multiple Exciton Generation, PV thermoelectric coupling …) with the double aim of finding innovative ways to approach ultimate conversion efficiencies and of demonstrating experimentally the approaches. …) will be developed with the double aim of finding innovative ways to approach ultimate conversion efficiencies and of demonstrating experimentally the approaches.

They will benefit for the combination of complementary skills and know‐how of the different partners on theoretical models (IRDEP/IPVF), material growth (RCAST, LAAS), photonics (C2N), device fabrication (RCAST, C2N, IPVF) and characterization (IPVF, RCAST).

Axis 2: New materials and systems for Perovskite solar cells, colloidal quantum dots solar cells and organic photovoltaics

Axis 2Interfacial contact and stability of perovskite material, in perovskite solar cells are critical issues for fundamental academic research work as well as for practical application of the perovskite solar devices. In this proposal, we expect less hysteresis and good stability when the perovskite crystals are grown in the well‐structured polymer matrix or/and another approach for minimizing the hysteresis by selection of suitable inorganic materials (such as perovskite based structure oxides) exhibiting smaller lattice parameter mismatch with perovskite crystal than conventional oxides as titanium dioxide. In the context of hysteresis free and long‐term stability perovskite solar cells, the present project aims at exploring the various possibilities for the surface engineering by using inorganic or organic molecules and macromolecules and designing stable perovskite solar cells.

This will involve strong collaboration and transversal work essentially between University of Bordeaux and RCAST, mostly the group of Prof. H. Segawa. Indeed, very recently, Camille Geffroy (PhD funded by IdEx University of Bordeaux) has shown promises of new hole transport polymer materials (HTM) developed at LCPO integrated in a perovskite solar cell device raising efficiency up to more than 20% and strongly affecting hysteresis behaviour. Still, stability remains an issue. Such progress could not have been made possible without such a real complementarity between the two groups.

Another aspect of this axis will be the exploration of strategy to reduce the toxicity of these technologies (lead-free colloidal quantum dots, water-based organic inks…).

Axis 3: Systems level innovation

Axis 3System‐level integration of PV modules is the key issue in order to enhance the utilization ratio of the PV power generation system and hence to reduce the levelized cost of electricity (LCOE).

In contrast to flat‐panel PVs, which system design is almost established for simple electricity generation, concentrator photovoltaic (CPV) modules are still on the way of developing system design. Necessity of accurate sun‐tracking, which is the heart of the high system efficiency of CPVs, imposes us a fundamental question whether thousands of CPV modules (unit combination between a lens and a high‐efficiency PV cell) should be installed onto a single huge sun‐tracker or the tracking should be controlled individually with smaller number of CPV modules.

These are indeed issues of system design and depend on a lot of boundary condition such as the technological level, cost of mechanical and electrical parts and geographical condition. It is therefore mandatory to develop multiple solutions for the CPV system design.

In this part, main research topics can be summarized as: Micro controllers at submodule level, association with storage, Heat management/thermoelectric hybrids, Internet of things, powering μ sensors, energy harvesting from various energy sources, RF and thermoelectric energy harvesting, Weather forecast and solar power output prediction, Ageing Characterization, modeling and default detection for solar cells and storage, elements both in cycling testing and real conditions.

Axis 4: Modeling and characterization techniques

Axis 4Materials and devices modeling is an important part of interpretation of experimental results and of device design.

On part of this axis will be dedicated to ab initio calculations to allow determining the defects formation in materials. These calculations occur at the atomic level. From the chemical nature of the defects we proposed to upscale such studies to determine the electrical nature of the defects such as the capture cross section. This kind of study is necessary to link the ab‐initio calculations to optical and electrical properties (part4) one can experimentally measure. This work will require multiscale modeling to link the atomistic properties to the macroscale properties.

Another part of this research axis will be dedicated to materials and interface characterization. To best design solar cells, or to correctly interpret the results of their characterization, basic properties of the heterostructures need to be accurately known. For new materials, including some III‐V alloys or heterostructures, notably with QD, or new hybrid materials, available optical data are neither complete nor consistent. Their measurement is often challenging and we need to develop methods for their accurate measurement.

Such achievements can be performed within the NextPV collaboration on the base of the expertise of the partners, RCAST, ILV and its CEFS2 platform for the chemical and electrochemical aspects and IRDEP/IPVF, C2N for the opto‐electronic one.