Monday of the 7th World Conference on Photovoltaic Energy Conversion saw the first technical sessions kick off, with plenary presentations in Areas 7, 9, and 5 and a special award presentation.

Dr. Paul Sharps kicked off WCPEC-7 with a fantastic plenary talk for Area 7, including a great mix of the history of space solar cells, the different mission orbits that these cells must operate in, and the future of the technology. The animation demonstrating the different orbits was particularly impressive. A big theme was the change of the industry moving towards space solar cells designed for specific orbital missions. By doing so, cell designers can ensure that the cell has the highest possible end-of-life efficiency (EOL), which is ultimately the constraint that spacecraft system designers must take into account. A recent tremendous interest in large LEO constellations has led to a big push to lower the cost of power on spacecraft at cell level and even more importantly at the system level. Next generation cell designs for space, such as the inverted metamorphic architecture, offer higher performance at EOL and provide several advantages at the system level.
Alison Ciesla, in the plenary for Area 9 presented a tribute to her father, Stuart Wenham, who was originally planned to give the plenary presentation. Prof Wenham, a Cherry Award recipient, contributed decades of world-leading research and will be remembered for his technical excellence and innovation, as well as his excellence in teaching and his enthusiasm and passion for solar-related research. His final work helped to understand the dual role of hydrogen in causing both problematic defects as well as passivation of problematic defects. As solar cells are being made with higher and higher efficiencies they become more sensitive to defects and can show up to 16% degradation associated with the LeTID effect: Light and elevated Temperature Induced Degradation. The presence of excess hydrogen induces the formation of defects that cause increased degradation. However, these defects are not stable in the long term, and as hydrogen is slowly eliminated from the cell, the problem disappears.
The Monday morning plenary session was concluded by the area 5 plenary speaker Ron Sinton. Ron gave insights on IV testing of cells and modules and the measurement uncertainties. Focusing on measurements in a production environment, he showed that the reference cell or module used for calibrating the measurement equipment together with a high reproducibility of the measurements are key for achieving low uncertainties. Optimizing your measurement procedures rather than relying on the letter grade of your sun simulator was the lesson offered. In addition, Ron pointed out that production cell and module testing offers the unique opportunity for highly sophisticated process control by extending beyond the light IV curve to perform suns-Voc measurements and determine the substrate doping as this enables a full device physics model to be used to analyze the cells manufactured. 
Professor Martin Green, from UNSW, was inducted as the new 2018 IEEE EDS Celebrated Member. He presented an excellent talk summarizing his many achievements throughout the years, starting in 1976, along the achievements of his students, many of whom are world leaders in academia and the PV industry. He notably mentioned the PERC cell that he invented in 1983, and the following high efficiency designs that set the benchmark for so long. He also highlighted the World’s 1st PV engineering degree started in 2004 at UNSW showing the transformation in PV that has taken place. He also outlined several paths for the future, including perfecting production and transfer of PERC cells, as well as increasing performance by 50% by stacking cells. 

Opening Keynote
In the Keynote address session the Conference Chair, Alex Freundlich highlighted the impressive numbers and diversity of the attendees at this conference, reflecting the truly global role that PV is playing. Larry Kazmerski then gave us an amusing history lesson looking back on 60 years since Vanguard 1 set the space race well and truly running, with big impacts for PV. Juzer Vasi then gave an update on the International Solar Alliance and the trajectory of PV both in terms of R and D and in increasing deployment and the efforts being made to ensure the future is solar. Dennis Flood then received the World Photovoltaic Energy Award for all of his contributions to PV over the decades. He used his acceptance speech to give the audience an inside look at the birth of the World Conference on PV Energy Conversion and Hawaii’s secret role it making it happen in the first place.

After breaking for lunch it was on to the first session of technical oral presentations. Here are some of the highlights provided by the session chairs. 
Area 6 - Advances in Perovskite Devices
Rohit Prasanna presented a promising approach for an all-perovskite tandem solar cells using a mixed-alloy of Sn and Pb in a two-terminal tandem solar cell reaching a 19.3% efficiency. Jeffrey Christians presented on phase-stabilized CsPbI3 nanocrystals, which help to improve stability compared to the thin-films made of the same material. Janez Krc has employed advanced three-dimensional optical simulations to determine the optimal geometry of micro-scale textured foils for perovskite solar cells. They found that a tetrahedral texture coupled with total internal reflection at the front interface plays the most important role. The topic of Luis Pazos-Outon's talk from the University of California, Berkeley was on the efficiency limit of lead halide perovskite photovoltaics.

Area 3 - Advances in III-V Solar Cells
The area 3 oral session on Advances in III-V Solar Cells hosted 6 excellent talks on the current and future status of high-efficiency III-V PV. Myles Steiner of NREL presented a 6J IMM target efficiency towards 50% employing a reverse heterojunction to overcome mobility issues with the top cell AlInGaP. Felix Predan (Fraunhofer ISE) presented the opportunities for wafer bonding on GaSb demonstrating the importance for passivation using an AlGaAsSb window layer and BSF. Alex Kirk from Microlink Devices presented the current status of ELO solar cells with AM0 efficiencies of 33.16% for 3 junctions and 34.31% for 4 junctions. Ryan France (NREL) showed the potential for combining compositional graded buffer with distributed Bragg reflectors to simultaneously change lattice-constant and improve absorption to upper sub-cells. Kevin Shulte also of NREL elucidated the barrier that can form from Zn diffusion between InGaP BSF to the GaAs junction, and remedied the issue via replacement of the BSF with C-doped AlGaAs. Naoya Miyashita from University of Tokyo demonstrated a dilute-N IMM cell overcoming issues with H-defects arising from MOCVD overgrowth.

Area 2 - Absorber Preparation
Niki reported remarkable results by joining efforts for fundamental studies on CIGS solar cells in a R &D consortium network providing a report on the TW workshop from April. Achard presented on tuning surface composition for high efficiency CIGS solar cells on polymer substrates at low temperatures. Campbell then showed successful lift-off of high quality CdTe layer using a MgTe sacrificial layer. Hutter presented a 7.9 % in house efficiency for antimony selenide solar cell formed by closed space sublimation. Finally Masuda reported on the transfer of lift-off CIGS solar cells to coloured plastic foil for aesthetical use on commercial cars.

Area 1 - Advanced Light Management and Spectral Shaping
Hung-Ling Chen from the Center for Nanoscience and Nanotechnology, Palaiseau France demonstrated 19.9% efficiency ultrathin GaAs. This was done using back contact nanoimprintiing structuring. Depth of nanostructuring is 100nm, spacing period is 700 nm. Ulrich Peatzold from Karlsruhe Institute of Technology, Germany showed that nanopatterning can increase tailored light absorption for use in multi-junction solar cells. This is done using nanoimprinting and the absorptance increases by 15% for values around the bandgap of the perovskite. Kentaroh Watanabe from the University of Tokyo studied thin-film multi-quantum well GaAs solar cells. Using an inverted growth design with sulphur instead of tellurium doping, epitaxial lift-off, gold-gold bonding and back side texturing, solar cells with no Te doping memory effect where fabricated and characterized. David Needel from Caltech proposed that LSC can be used to increase the module efficiency of tandem solar cells with properly chosen luminophores and demonstrated by Monte Carlo ray tracing simulation. Gabriel Cossio from UT Austin, presented large-area III-V solar arrays incorporating on the moth-eye type nano-textured PET substrate, which are fabricated by self-assembly of nanospheres and plasma etch. the prototype module shown enhanced Jsc by better collecting the diffused light than the planar reference. Rebecca Saive from California Institute of Technology and University of Twente, studied the use of indium tin oxide as a substrate for perovskite solar cells and panels. The substrates are patterned to produce a superstrate filled with silver lines 5 microns wide and 15 microns high to increase short circuit current by more than 1 mA/cm 2 and keep transparency higher than 99%.

Area 5 - Crystalline Material Characterization
Great results on modelling the concentration of H 0 in silicon from Ran Chen, UNSW which is a helpful basis to understand diffusivity of hydrogen in silicon. Pavel Dutta presented an in-depth characterization of grain boundaries in GaAs on flexible substrates, providing further insight into this system as a low-cost alternative to traditional GaAs PV devices. Rhett Evans gave us new statistical insights in fill factor prediction from brick level lifetime data in multi PERC cells. Solene Bechu presented comprehensive GD-OES data of III-V layers to probe subsurface device layers. Johnson Wong presented a new IR absorption technique to determine CZ silicon from transient photoconductance data.

Area 4 - Optical Coatings, Passivation and Light Management
EPFL showed an increase in performance by 0.3% by adopting SiOx plasma and low T that facilitate crystal growth. Fraunhofer CSP presented a new method using plasma texturing on cell level. Technical uni versity of Denmark presented RIE results with reflectance below 3% with 2 min processing and a surface recombination with AlOx of 13 cm/s. Rebecca Saive showed how specially designed effectively transparent front and rear fingers can increase light trapping and reduce optical shading which might be beneficial for bifacial solar cell applications. Cong Tanh Nguyen reported how addition of reusable glass microparticles to KOH based texture solution can reduce reflectivity and texturing time significantly. Jian Yu presented how the introduction of a SiOx/SiNx stack on top of the TCO layer for HIT solar cells leads to a 23.5% solar cell efficiency.

Area 9 - Field Studies
Takashima’s talk clearly delineated that the field aged PV modules may pass the STC tests but may not pass in the field operating conditions at above 50C due probably to the cell interconnect failure. This implies that the field aged PV modules need to be tested not just at STC but also other higher temperature conditions, including for warranty claims.

After a quick break for reviving, it was on to the first poster/visual presentation session. A number of different Areas were represented and lively discussions ensued as some excellent work was presented.

The following presentations were the recipients of awards, broken down by Area:

Area 3
#97 - Enabling low-cost III-V/Si integration through nucleation of GaP on v-grooved Si substrates 
E Warren, E Makoutz, T Saenz,  et al    
Area 9
#214  Development of Low-Cost, Crack-Tolerant Metallization for Solar Cells
O Abudayyeh, C Nelson, A Chavez,  et al       
Area 5
#130  Inspecting series resistance effects and bypass diode failure using contactless outdoor photoluminescence imaging
R Bhoopathy, O Kunz, M Juhl,  et al     
Area 8
#212 The Need for a New Parameter on PV Modules Datasheet: Shading Tolerability 
H Ziar, S Mishra, O Isabella,  et al       
Area 6
#170  Formamidinium + Cesium Lead Triiodide Perovskite Thin Films: Optical Properties and Devices 
B Subedi, L Guan, Y Yu,  et al   
Area 2
#70 Transparent Wide-Gap Chalcopyrite CuGaSe2 Thin-Film Photovoltaics with Noble Dot-Patterned Mo p-Electrode
S Shibasaki, N Nakagawa, S Yoshio,  et al        
Area 4
#107 Silicon Heterojunction Solar Cells on Quasi-mono Wafers
Jan Haschke, Maulid M. Kivambe, et al.

After a short break it was time for the Welcome reception where some lively conversation took place, at the same time a networking event for Women in PV was taking place. Both of these events warming everyone up for the special international session where the experiences and plans for The US, Europe and Japan were reviewed and an expert panel discussion followed. Attendees were given an excellent overview of the key takeaways from decades of experience in deploying PV and some of the lessons learned that have led to the strategies being implemented.
So the first day of the technical program of the 7 h WCPEC is finished!

Be sure to stop by the EDS membership booth, located in the exhibit hall, next to the poster lounge by the stairs, to learn about the EDS membership promotion deals available to WCPEC-7 attendees. EDS members enjoy a host of important benefits including free, unlimited online access to the IEEE Journal of Photovoltaics. So stop by to learn more. Don't miss this opportunity to become part of the EDS community!