35th EU PVSEC, 24 - 28 September 2018
SQUARE - Brussels Meeting Centre, Brussels, Belgium

24 August 2017

Challenging the Theoretical Solar Cell Efficiency Limits - Discussed at Upcoming EU PVSEC in Amsterdam

Step by step PV scientists are improving cell efficiencies – and the latest 26.33% record of Kaneka is another step narrowing the already close gap to the theoretical efficiency limit of 29.4% for single-junction crystalline silicon based solar cells. So what’s next?

At the same time, that companies are improving commercial cells, researchers are working on advanced materials and concepts to overcome the theoretical efficiency limitation. The upcoming 33rd EU PVSEC in Amsterdam from 25-29 September will provide insights into such advancements in programme topic 1 “New Materials and Concepts for Photovoltaics Devices”. This topic is represented with 3 talks in the plenary session, 29 oral presentations and 78 posters, resulting in a total of 110 scientific papers from scientists of leading research centers in Europe and many other parts of the world.

 

The Plenary Session on New Materials and Concepts for Photovoltaics Devices, titled Stairway to Higher Efficiency, serves also as the Scientific Opening Session of this year’s EU PVSEC (25 September 08:30 to 09:30). Of the plenary’s three presentations, two will be focused on tandem cell architecture, while the first talk from the Netherlands as the host country of this year’s EU PVSEC will be about semiconductor attributes of a perovskite material

Dutch research laboratory AMOLF, which carries out fundamental research in complex material systems, will present its study results on Indirect to Direct Bandgap Transition in Methylammonium Lead Halide Perovskite. Solar cells based on organic-inorganic hybrid perovskites have reached an efficiency level of over 22%. The prototype material in this family, methylammonium lead iodide perovskite (MAPI), has been considered a direct bandgap semiconductor. However, it exhibits carrier lifetimes in the microseconds range, which is long for a direct bandgap semiconductor. AMOLF has investigated the seemingly contradicting properties of efficient absorption in direct bandgap materials and the long carrier life time of MAPI. Theoretical calculations predict a light indirect bandgap for MAPI. AMOLF will present the basis of its theory.

A way to overcome the theoretical limit for single junction crystalline cells is “simply” by moving to two junction cells. While tandem silicon thin-film cells have been tried unsuccessfully in the market in the past (efficiencies were too low, costs to high), combining a traditional silicon wafer based cell with a second absorber material on top in a dual junction tandem solar cell is something promising researchers are currently working on. Based on this approach, the German Institute of Solar Energy Research Hamelin (ISFH) will present its latest results for “Maximum Power Extraction Enabled by Monolithic Tandems Using Interdigitated Back Contact Bottom Cells with Three Terminals”. Though four-terminal (4T) configurations have proven to be suitable for attaining high efficiencies (31.5% achieved recently by a joint research group from ISFH and NREL), their cost effective implementation is questionable. Two terminal (2T) tandem cells, on the other hand, suffer from current mismatch that reduces conversion efficiency (28.1% reported by the same joint research group). As an intermediate alternative of these two configurations, ISFH evaluated a three-terminal (3T) tandem device. Here, a c-Si interdigitated back contact cell with an additional front electrode is used for the bottom cell. ISFH will discuss the details of the device and the physics of such a cell structure.

One option for a top cell in a silicon-based tandem structure is using high-efficiency III-V technology (which is generally used for high concentration PV or space cells). Europe’s largest solar research center Fraunhofer ISE will present the latest progress for a “Monolithic III-V//Si Multi-Junction Solar Cell Exceeding an Efficiency of 31%”. This record efficiency has been attained with a two terminal GaInP/AlGaAs//Si solar cell. ISE’s presentation will focus on the status of silicon based tandem solar cell using direct wafer bonding to III-V top cells and discusses different technical possibilities and their respective limitations. III-V//Si two-terminal solar cells have been produced by bonding a two-junction AlGaAs/GaInP solar cell on top of a silicon bottom by means of surface activated wafer bonding. In order to investigate the recombination at the GaAs/Si bonded interface, different passivation configurations are evaluated, such as a bare silicon surface, SiNx passivation or GaAs bonded wafers, as well as a varying dose in P-implantation. ISE’s presentation will discuss the results of these experiments.

The ‘New Materials and Concepts for Photovoltaics Devices’ section of the upcoming EU PVSEC has 5 more oral sessions and one slot for poster presentations.

Oral sessions of New Materials and Concepts for Photovoltaics Devices

Monday 25th September

  • Devices & Characterisation (13:30 – 15:00)
  • Optics and Materials (15:15 – 16:45)
  • Advanced and Novel Concepts for Very High-Efficiency Solar Cells (17:00 – 18:30)

Wednesday, 27th September

  • Advanced Materials and Technologies for PV Modules (08:30 – 10:00)
  • New Materials and Advanced Applications for Photovoltaics (13:30 – 15:00)

Poster Session:

Wednesday, 27th September

  • Fundamental Studies / New Materials and Concepts for Cells and Modules (15:15 – 16:45)