Thin Film

In this paper we discuss recent advances in the field, with a focus on potential device designs and manufacturing processes.

Two-terminal tandem solar cells based on perovskite/silicon (PK/ Si) technology represent one of the most exciting pathways towards pushing solar cell efficiencies beyond the thermodynamic limit of single-junction crystalline silicon devices. While laboratory efficiencies of these tandem cells have risen to very impressive levels, many important innovations towards enabling their eventual manufacturability have also been made in this rapidly evolving field. In this paper, a number of these processing innovations are highlighted in order to give a more complete view as to the viability of scaling up the processing of these devices. Specifically, the focus is placed on how today’s crystalline silicon process flows could be adapted in order to allow existing cell lines to produce PK/Si cells.

This paper provides a concise overview of existing c-Si-based 2-, 3- and 4-terminal tandem technologies, summarizes the current development status, and sets out the future roadmap. In addition, a discussion is included of what will be required over the coming years to bring these promising technologies to market, enabling commercial efficiencies above 30%.

This paper discusses, at both the cell and the module level, the balance between the advantages and drawbacks of increasing the cell bifaciality from a typical value of 90% towards 100%, or decreasing it towards that of monofacial cells (0%).

Heterojunction technology is currently a hot topic actively discussed in the silicon PV community. Hevel recently became one of the first companies to adopt its old micromorph module line for manufacturing high-efficiency silicon heterojunction (SHJ) solar cells and modules. On the basis of Hevel’s own experience, this paper looks at all the production steps involved, from wafer texturing through to final module assembly.

Tandem solar cells combine several solar cells with different photoabsorbers, stacked in a descending order of bandgap energies. They come in many flavours, but one promising combination is a bottom cell of c-Si or copper indium gallium selenide (CIGS) and a top cell of perovskite. Perovskite solar cells are thin-film solar cells with many advantages, such as a low-cost, high-throughput sheet-to-sheet and rollto- roll production, and a tuneable bandgap. Their long-term instability, however, is a challenge that needs to be overcome in order to make these cells a success. In this paper it is demonstrated that, by combining comprehensive loss-reduction strategies with effective large-area fabrication, perovskite-based tandem solar modules have the potential to yield power conversion efficiencies (PCEs) that are significantly higher (PCE of up to 45%) than those of established PV technologies, and can be manufactured on an industrial scale.

The EU Horizon Sharc25 project has provided deep insights into highly efficient Cu(In,Ga)Se2 (CIGSe) thin-film solar cells fabricated by lowand high-temperature co-evaporation using advanced characterization methods, analytical tools, device simulation, and density functional theory modelling. This complementary approach led to a continuous knowledgedriven development and improvement of the CIGSe absorber. Based on optimized chemical composition, profiles, and alkali metal post-deposition treatments (PDT) using KF, RbF, and CsF, the CIGSe cell efficiency could be substantially increased to a record value of 22.6%. Due to additional modifications at the absorber/emitter (replacement of standard buffer system by a combination of thin CdS and TiO2) and back contact/ absorber (introduction of Al back reflector in combination with InZnO diffusion barrier) interfaces, in particular the short-circuit current could be increased. Furthermore, passivation layers in combination with point contact schemes at the CIGSe front and back side were developed and are still under investigation.

Two factors have coincided to stimulate the recent spur in interest for hybrid tandem PV technology based on crystalline silicon – the fact that balance-of-system (BOS) costs are increasingly dominating turnkey system costs, which strengthens the effect of high efficiency in reducing Wp costs, and the discovery of perovskite solar cells as a promising low-cost wide-band-gap partner for crystalline silicon (c-Si). This paper presents the progress and analysis of four-terminal (4T) perovskite/c-Si tandem technology at ECN part of TNO, with perovskite technology development carried out within the Solliance research organization.

To realize power generation everywhere, customers and designers are eager for PV solutions offering total design freedom for seamless integration into everyday life. This trend becomes even more important if the ‘mega city’ development is taken into account: more and more people will live in city environments in the future while classical PV technologies do not offer proper solutions for this context.

Nowadays, there is a worldwide production capacity of about 5GW of thin-film module technology. In total, an estimated cumulative installed capacity of 15 to 24GW exists (5-8% of 300GW installed worldwide in 2016). But how serious is the threat of PID in this thin-film fleet?