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. In this sense it is important to work. 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 nanoimprinting 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/cm2 and keep transparency higher than 99%.

Area 5 - Crystalline Material Characterization

Great results on modeling the concentration of H0 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 inline infrared

optical measurement technique to determine doped layer properties in silicon wafers.

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, S Han, 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.

Additionally, the Area 9 Poster Session Chairs provided highlights on the session. Sang Han's poster on

low cost, crack tolerant metallization received the award for the poster session on field studies. They showed

that carbon nanotubes embedded in matrix of silver metallization can reduce the possibility of solar cell

cracks leading to power loss. Kaushik Roy Choudhury's poster (nominated) discussed a relatively new

failure mode in certain types of backsheets which results in cracking of inner layer of backsheets and can

be detected by shining light from back side of the module. Marjila Burhanzoi's poster (nominated)

presented a method to detect faults in PV modules by measuring magnetic flux densities along the busbars

and the results showed good correlation with EL measurements.

In addition to the nominated posters, several posters reported interesting findings. For example, Rajiv

Dubey reported that cell cracking and encapsulant browning have been major causes leading to poor

performance of certain systems in India. Laura Bruckman reported a generalized spatio-temporal model

with the response surface methodology to evaluate and predict the large scale backsheet degradation in the

same site during lifetime without measuring individual samples.

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 7h WCPEC is finished!