The specific scientific objectives of KESTCELLS are:
a) To achieve a much deeper understanding of the fundamental properties of kesterites which determine their optoelectronic properties, including: the band-gap, energetic position of the bands and ionisation energy of defects, the crystal structure and the structural origin of intrinsic point defects and the fundamental vibrational properties, as well as their dependence on the compound composition and growth process;
b) To identify and understand the role of secondary phases in the characteristic performance of the devices, as well as their dependence on the kesterite composition and growth parameters;
c) To improve the knowledge on the main doping mechanisms responsible for the p type conductivity of the layers and to develop suitable processes for its control;
d) To apply this knowledge for the design and development of new kesterite based solar cells with improved characteristics; using processes with low environmental impact that are compatible with industrial scale-up at mass production levels; and defining and identifying back contact, buffer and window materials better adapted to the kesterite absorber layers in these devices,
e) To optimise and demonstrate these processes for the achievement of cells with an efficiency > 10% without the involvement of toxic or hazardous reagents such as hydrazine. The aim is to bring the world record for the efficiency of these cells to Europe.
The project is structured in six strongly complementary and interdependent WPs, that are summarised in Table 1. In addition, there are WPs that are specifically devoted to Coordination and Management (WP9), Coordination of the Training activities (WP7) and Dissemination and Outreach activities (WP8).
|Work package No||WP Type||Work package title||Deliverables (D) / Milestones (M)||Lead
|Start month||End month|
|WP1||RTD||Fundamental properties of kesterites||D1.1,D1.2,D1.3D1.4M1.1,M1.2,M1.3||UL||1||41|
|WP2||RTD||Develop. of absorbers by PVD and chemical based processes||D2.1,D2.2,D2.3,D2.4,D2.5M2.1,M2.2,M2.3||NU||3||43|
|WP3||RTD||Implementation of solar cells||D3.1,D3.2,D3.3 M3.1||HZB/E-I2||9||47|
|WP4||RTD||Cell & process monitoring||D4.1,D4.2,D4.3D4.4M4.1, M4.2||NEXCIS||7||48|
|WP5||RTD||Modelling & design||D5.1,D5.2 M5.1||AMU||8||46|
|WP6||RTD||Industrial scale up, transferability and exploitation||D6.1,D6.2 M6.1||ASNT||22||48|
|WP8||DISS/OUT||Dissemination & Outreach||D8.1, D8.2, D8.3||IREC||1||48|
|WP9||MGT||Coordination||D91, D9.2, D9.3||IREC||1||48|
WP1 – analysis of the fundamental properties of kesterites. A deeper knowledge on these properties is a strong prerequisite for the further development of these technologies. This WP will provide significant data on the material properties (crystalline and defect structure, zone centre phonon structure, band gap and band alignment, electronic transport and optoelectronic parameters) and their dependence on growth parameters. These data are essential for the development of the processes related to synthesis of the absorber layers (that will be developed in WP2), the implementation of the cells (WP3) and their modelling and design (WP5). WP1 will also have a strong interaction with the IRPs involved in WP4 (Cell and process monitoring), since the knowledge of the fundamental properties of kesterites will be essential for the analysis of the cells, including the identification of different phases and structural inhomogeneities in the polycrystalline absorbers (that requires a previous knowledge on the crystalline (XRD) and vibrational (Raman) properties of the material), and the device characterisation (which will require a previous knowledge of the defect structure, doping and transport properties of the material).
WP2 – synthesis of the absorbers using PVD and chemical based routes (WP2). PVD based processes are very well known from CIGS PV technologies, and are extensively used in their industrial implementation. On the other hand, chemical based routes have additional interest because of their potential to achieve lower manufacturing costs and their higher compatibility with industrial production at mass production levels. This will allow developing a comprehensive knowledge of the processes and mechanisms involved in the synthesis of the absorbers, addressing specific relevant issues as those related to the control of doping and secondary phases. The comparative analysis of the absorbers and cells fabricated by the different routes will allow defining the most cost efficient methods for absorber deposition.
WP3 – implementation of the absorbers developed in WP2 in solar cells will be performed in WP3. Options for replacement of the CdS buffer layer in the device include materials such as ZnS and ZnSe that have already produced promising results with CIGS and first results on kesterite based devices. However, depending on the results on band alignment, new buffer materials might be needed. This will allow the establishment of initial processes for a Cd free kesterite based PV technology, in order to fully exploit the potential of these materials for the development of cost effective sustainable technologies with low environmental impact and reduced strategic energy dependence of Europe on third countries.
WP4 – in this WP a detailed characterisation of the layers and processes will be developed in addition with the analysis and monitoring of the cells, in order to perform a systematic study of the relevant interfaces in the back contact/absorber/buffer/window heterostructure, and to define the most suited materials for optimised devices using kesterite absorbers.
WP5 – all these activities will be developed in close correlation with WP5, providing with specific inputs on materials and device parameters that are required for the simulation of the devices and, in turn, following the main design rules deduced in WP5 for the implementation of cells with higher efficiency.
WP6 – finally, the technological processes developed in the project will be subjected to an industrial implementation and exploitation analysis, studying the innovation actions that are required to improve the competitiveness of the European PV industry. Analysis of the transferability of the processes to industrial production scale is a relevant activity in order to define the most cost efficient processes, bearing in mind the long term objective of the project (achievement of a significant share on PV technologies in the energy production in Europe by the development of sustainable low cost PV technologies compatible with mass production requirements). Private companies involved in the consortium will have a significant role in the development of these activities, and will provide the Universities and Research Institutes with complementary expertise on management and implementation of industrial production lines, as well as with technology exploitation and market analysis.