Tuesday of the 7th World Conference on Photovoltaic Energy Conversion saw the Cherry Award Ceremony

as well as that for the PVSEC Awards and the WCPEC Young Professional Award. Before these took place

the technical sessions kicked off with the plenaries for Areas 1, 6, and 10.

Area 1 saw Prof. Kylie Catchpole give an update on the latest developments in

the area of tandem solar cells presenting world record performance of 26%

efficiency for a four-terminal tandem perovskite-silicon device. She also reported

on the demonstration of 23.9% efficiency in a perovskite/CIGS tandem solar cell.

Finally, she detailed remaining hurdles to get to 30% efficiencies and long

operational lifetimes namely substitution of organic layers with inorganic

materials and incorporation of rubidium in the perovskite.

Dr. Anders Hagfeldt gave an enlightening talk, expanding on the history of

perovskite development from predecessor technology to the present state-of-the-

art. He discussed the success of the perovskite system from the viewpoint of its

diversity of options - in materials, chemistry, device structure, and applications -

that facilitate many different paths of development. In order to achieve even

greater performance success, however, we must look beyond the perovskite itself

and also evaluate the systems and structures it inhabits.

In Area 10, Dr. Sven Teske shared his latest study on “The role of solar

photovoltaic in decarbonization scenarios”. His 2-degree scenario expects doubling

of the global PV market by 2021 to over 200GW/year and around 350GW/year by

2030. Cumulative PV capacity is expected to reach 3.8TW and 11TW in 2030 and

2050 respectively. In 2050, PV can globally supply around 30% of total generation.

After a coffee break it was then time for a well-attended poster session with contributions from Areas, 2,3,

4, 6, 8, 9, and 10. The following presentation were recipients of the poster awards for their respective areas:

Area 3

#302 Design and Evaluation of Low-concentration Static III-V/Si Partial CPV Module for Car-

rooftop Application

D Sato, K Lee, K Araki, et al

Area 8

#385 Optimization study of a photovoltaic-photochemical hybrid system (SOLWAT) for meeting

the needs of electricity and clean water

N Pichel Mira, M Vivar García, M Fuentes Conde

Area 4

#317 Implications of Laser-Doping Parameters and Contact Opening Size on Contact Resistivity

J Huyeng, M Ernst, K Fong, et al

Area 10

#430 Algorithms to Effectively Quantize Scenarios for PV Impact Analysis using QSTS Simulation

J Deboever, S Grijalva, M Reno, et al

Area 2

#258 Area-selective electrodeposition of Cu(In,Ga)Se2 micro islands for micro-concentrator solar

cells

D Correia, D Siopa, P Salomé, et al

Area 9

#415 Corrosion of the Glass and Formation of Lead Compounds in the Metallization by High

Temperature and High Humidity Test of Crystalline Silicon PV Module

T Semba, T Shimada, K Yamada, et al

Area 6

#359 Impact of Epoxy Encapsulation on Device Stability of Large-Area Laser-Patterned Perovskite

Solar Cells

Z Song, C Wang, D Zhao, et al

After taking in lunch, attendees returned for the two afternoon technical sessions. In the first group, from

1.30 to 3.00 pm the following highlights were provided by the session chairs:

Area 2

Hauschild: The reason for high module efficiency of 18.2% with Na-doped In2S3 buffer was investigated.

It was found that Na-doping leads to an Eg increase and to a spike-like CBO at the buffer-absorber interface.

The spike can be flattened by annealing at 200C, leading to a favourable CBO. Hildebrandt: Using NH2OH

room temperature deposition at room temperature within 15 min. and without any post treatment, an CIGS

solar cell efficiency of 14-15% could be reached. Liyanage: Perovskite was suggested as back contact

electron barrier to reduce back contact recombination. Solar cell modelling showed increase in device

performance by increase of Voc and FF. Cui: A new approach with ZnSnO buffer layer for CZTS with

improved performance compared to the CdS reference was presented. Hayakawa: It was shown that with

a highly doped CdS buffer layer in CIGS solar cells, high efficiencies can be maintained independent from

band offset conditions and interface defect concentration. An increase in carrier concentration in CdS was

realized by doping with In, leading to an increase in Voc and FF.

Area 4 - Homojunction Devices and Technologies

E-ton Solar presented a novel low cost Al-doped paste for the fabrication of PERL solar cells, while

Fraunhofer ISE presented a low cost boron doping paste for the fabrication of high efficiency back contact

back junction solar cells. Fraunhofer ISE also presented their latest results regarding low pressure diffusion.

They reported regarding different glass thicknesses as a function of the POCl3 process conditions. The

University of Konstanz presented a high efficiency gettering process by APCVD process for mc-Si wafers,

while ISC Konstanz presented a nice review on their high efficiency low cost ZEBRA solar cells by

printing. The University of Meiji presented their developed n-type solar cell using thin wafers and front

junction. High current were obtained on 83 micron thin wafers.

Area 6 - Understanding Perovskite Optoelectronic Properties

Giles Eperon reported on a surprising difference in the biexciton Auger recombination in hybrid and

inorganic perovskite solar cells. His results suggest that organic perovskite nanocrystals should be favoured

for LEDs and lasers. Fabian Ruf reported on a novel method to measure the temperature-dependent bandgap

and determine the exciton binding energy of perovskites. Susan Schorr reported on the role of cations and

anions in hybrid perovskites. The organic cations contribute to screening, while the PbX3 network is

responsible for the electronic structure. She also discussed the effect of annealing to improving the stability

of cubic perovskite phases. Hannah Funk presented on the extraction of microscopic composition

information on CsPbBr3 films by identifying the phases present on the microscale using EDX and

cathodoluminescence mapping.

Area 7 - Characterization Technologies for Space PV

C. Zimmermann explained the extraction of sub-cell I-V curves from 3J and 4J solar cells by pulsed laser

illumination taking into account the optical coupling effect using selective optical bias. Cell base doping

and built in voltage can be also evaluated. EOL and BOL cells can be evaluated. C. Baur described a method

of using differential spectral responsivity calibration to measure the absolute spectra responsivity to

calculate a calibration value to be used to calibrate solar simulators in the absence of a balloon calibrated

standard. Additionally, they investigated how to address uncertainty in the AM0 solar spectrum by

analyzing balloon results with recent AM0 solar spectrum. Philip T. Chiu compared AIAA, ECSS and

JAXA radiation testing methods to compare retention factors after each method. Chiu recommended on

orbit data to corroborate ECSS or AIAA MEO missions. Yuichi Shibata investigated recovery of open

circuit voltage in electron irradiated InGaP cells. Voc increased after light soaking. Recovery on depends

on the number of photogenerated carriers. Phosphorus related defects contribute to the recovery because

the particle energy dependence on the activation energy for annealing was of the same order. J. Grandidier

described the parameters needed to make a solar cell work on Venus such as operating at over 300 and 100

degrees C. Also Venus's solar spectrum is extremely dependent on the altitude due to the H2SO4 gas

atmosphere. Using a combination of modelling and experimental results, Grandidier arrived at a solar cell

design that can work well at 21km 300C and 47km at 100C and fabricated an optimized solar cell at 21km

Venus altitude and 300C.

Area 9 - Backsheets and UV testing

X. Gu spoke on UV testing of backsheets, reporting on degradation as a function of spectral band within

UV with the shortest wavelength causing most damage. X. Gu the presented again, this time looking for

ways to duplicate backsheet mechanical failures seen in field. UV exposure plus mechanical strain yielded

cracking. X. Gu then backed up again to look at polyimide backsheet cracking with chemical degradation

observed after UV exposure. Material embrittles but no cracks observed as degradation only extends

partway into material. Cracks only appear after application of tension. Nancy Phillips looked at replicating

environmental stresses through multiple pathways. Can accurately accelerate field degradation by

sequential testing- heat, light and moisture, followed by mechanical and repetition. A. Morlier spoke on

UV Fluorescence testing of EVA. Transmission decrease (increased yellowing) has linear correlation with

fluorescence of EVA, which can be measured quicker, and depends on UV absorption in EVA. No

yellowing with no UV absorber in EVA. H. Gopalakrishna spoke on accelerated testing of encapsulant

browning with temperature. UV Fluorescence imaging was used for accurate fast detection of browning

and cracks.

Area 10 - Grid Integration of PV

M. Perez gave a good talk that described how a PV/wind/Storage system for Minnesota made economic

sense. M. Qureshi discussed new approach to evaluate distribution impacts using volt/var control that can

speed up computations by 90%. S. Akagi discussed benefits of reduced tap changes with a battery energy

storage system on distribution circuits. M. Reno described another approach for improved QSTS

simulations. J. Johnson discussed how send information to distributed inverters in a manner to optimize

performance across a larger system that was simulated using power hardware in the loop. C. Bayer gave an

inspiring talk on how solar can be used to power the transport sector.

After a break to re-charge it was onwards with a further set of oral technical sessions covering work in

Areas 2, 3, 4, 5, 6, 8, and 9. Here are some of the highlights provided by the session chairs:

Area 3 - CPV Modules and Systems

Vahan Garboushian gave a brief history of CPV and provided an inspirational perspective on the future of

CPV, including some innovative build-integrated PV concepts that Arzon Solar is currently developing.

Alex Grede discussed current progress in the development of a shape memory alloy based micro-tracking

system that shows promise for enabling flat-plate like CPV. Tian Gu talked about a hybrid CPV system

that makes use of a patterned Si cell to capture diffuse light and provide geometric concentration to

embedded III-V micro-concentrators. Matthew Escarra described a hybrid thermal/PV concentrator system

that shows promise for providing highly economic heat power. Kenji Araki discussed issues in CPV related

to fluctuations in atmospheric conditions using Monte Carlo simulations, which indicated that optimal cell

design depends strongly on not only air mass, but also atmospheric quality and sub-cell radiative efficiency.

Area 4 - Silicon Material, Feedstock and Wafers: Technology

D. Macdonald from Australian National University presented for A. Liu with excellent gettering observed

for thermally diffused n-type and p-type polysilicon contacts with a reduction in the concentration of

interstitial iron ([Fei]) by more than 3 orders of magnitude. [Fei] is gettered into the boron-rich layer, which

can be removed post processing. Chuanke Chen from LERRI Solar presented results on low LID Ga-doped

p-type Cz solar cells. Daniel Chen from UNSW presented record Voc for SHJ solar cells on p-type Cz and

multi. C. Sen from UNSW presented method to eliminate LeTID using RTP processing. Elimination of

LeTID is reported with several Temp profile and t down to 5s and T of 500 C. P Hamer from University of

Oxford (now UNSW) presented a study on the behavior and transport of H and its effect to the contact

resistance. Highlighted reversible changes in series resistance by using anneals with forward/reverse biases.

R. Basnet from Australian National University presented 718 mV Voc for silicon heterojunction solar cells

using tabula rasa and phosphorus diffusion gettering to improve the lifetime of n-type Cz UMG silicon

wafers.

Area 5 - Microscopic Characterization Techniques

Thomas Fiducia gave an excellent presentation about the effect of Se at grain boundaries in CdTe solar

cells measured by cathodoluminescence, combined with nanoSIMS. Thomas Hannappel presented results

on the electronic properties of individual III-V nanowires using a multi-tip STM setup to determine doping

profiles along the nanowires. Chuanxiao Xiao gave an impressive presentation about the use of combined

microscopy techniques for the characterization of grain boundaries in CdTe solar cells.

Area 6 - Perovskite Material Development

Marronier showed in his presentation that "Cesium is the new black". Based upon theoretical calculations

the phonon modes and anharmonicities in CsPbI3 were discussed. By synchrotron XRD T-dependent

structural phase transitions were explored, showing also the existence of metastable phases. Prasanna

discussed band gap engineering by substituting Pb by Sn in (Cs,FA)PbI3 and (MA,FA)PbI3. Stability issues

were investigated showing that the instability is a thermally induced formation of recombination centers.

Petzold discussed the challenges faced in ink jet printing of halide perovskite thin films, with the case

shown for a triple cation perovskite. By printing an additional luminescent dye a coloured solar cell can be

achieved, whereas the impact on EQE is quite low. Moore spoke about successfully laminating perovskite-

perovskite interfaces and full devices, which in principle removes the issues of solvent compatibility of

different layers. Delamination occurs at the perovskite-transport layer interface, which is promising for

perovskite-perovskite lamination. It is a first step on the way to laminating perovskite-perovskite tandems.

Conings discussed gas quenching in perovskites with some examples, highlighting the excellent results

from Stanford employing his technique and the scalability.

Area 8 - Bifacial PV Modules

Amir Asgharzadeh presented a comparison of bifacial system production with different configurations

using RADIANCE software. Silvana Ayala Pelaez showed a 7% bifacial gain on a system installed in

Klamath Falls, Oregon (compared to 6.7% modelled). Djaber Berrian used an optical view factor model

(MoBiDiG) to evaluate the performance of tracking and fixed PV arrays. David Bowersox presented a

comparison of using inverted-V, U and flat reflectors to enhance the power output of the bifacial modules.

Yuanmin Li presented the gain of bifacial systems including tilt installations and vertical installation for

HIT modules. Daniel Riley showed potential MLPE advantage for bifacial systems to deal with non-

uniformity of portrait, front-shading and varying reflections.

Area 9 - PV System Safety and Components

Nicholas Bogdansky from TUV discussed requirements for safety as well as performance measurement for

Energy Storage System installations. He introduced a system performance index. Evaluation of cyber

security is critical as well as attention to installation requirements. Qing Xiong from Xian Jiaotong

University discussed DC arc fault detection and localization using parallel capacitors. Spectrum analysis of

capacitor currents provided frequency spectrum coefficients can be utilized to localize the fault. Polarities

and spectrum in addition to amplitude is used to discriminate faults. Jack Flicker from Sandia National

Laboratories spoke about Hazard analysis of Firefighter interactions with PV systems on roofs. Ungrounded

arrays have significantly less hazard than grounded arrays. This work will be utilized in the upcoming UL

3741 standard. Janine Freeman from NREL discussed a method for evaluating impacts and costs from PV

component faults and failures. Simulations of reliability or and repair time improvement scenarios.

Doubling the time to failure of the inverter and eliminating the inverter 15year replacement assumptions

offers the most benefit. Narendra Siradkar from IIT Mumbai proposed recommendations to revise the

bypass diode test in IEC 61215 to incorporate effects of PV module mounting configuration and climate of

deployment. Diodes in hot climates on roof do experience significantly higher temperatures (200C). The

temperature test is more representative for rack mounted modules and needs to be revised for roof mounted

modules. A BPDT test condition of 1.15Isc @ 100C for first part and 1.4Isc @ 100C is proposed. Arno

Smets from Delft university of Technology spoke about identifying malfunctions in PV systems

automatically in real time using massive online PV yield data. He demonstrated a novel approach that can

be utilized by many stakeholders and the possibilities for big data in PV.

It was then time for the Awards ceremony. First up, one of the conference’s most prestigious awards, the

2018 Young Professional Award was presented to Dr. Adele Tamboli of the National Renewable Energy

Laboratories for her significant contributions to photovoltaics during her early career. The group of young

PV scientists who have achieved a spot on this very limited list of people receive a plaque, a monetary

award, free conference registration, and an invited talk slot in the area of his/her choice. Congratulations

Dr. Tamboli!

Next, the Tuesday evening awards ceremony honoured the William Cherry Award winner Dr. Vasilis

Fthenakis from Brookhaven Laboratory / Columbia University with Fernando Guarin presenting the plaque.

Christiana Honsberg provided the laudation that included seminal aspects of Prof Fthenakis’s research and

pivotal moments in his life. Dr. Fthenakis then treated the audience to a summary of his life’s research at

the interface of energy and the environment that catalyzed PV technology deployment worldwide. Prof

Fthenakis delivered an inspiring talk on the recycling of PV materials and the sustainability of various

technologies, materials, manufacturing processes.

After this, the representatives from the Asia-Pacific PVSEC presented two unique PVSEC awards to Prof.

Takahiro Wada and Prof. Donghwan Kim for their outstanding contributions to photovoltaic science and

technology development. Prof. T. Wada has been one of the world’s leading researchers in polycrystalline

thin film solar cells. He was a project leader at Matsushita Electric (Panasonic), and his group achieved

efficiency of about 18% by originally developed composition-control technology for Cu(In,Ga)Se2 solar

cells in 1996. He is currently a professor at Ryukoku University, and he is also a fellow of The Japan Society

of Applied Physics (JSAP). Prof. D. Kim has been working on photovoltaic since he got his Ph.D at Stanford

University in 1993 on p-type doping of CdTe solar cells, and he demonstrated efficiencies over 12%

reported at the WCPEC-1 in Hawaii in 1994. Currently, his main research area is high-efficiency Si solar

cells. He was the president of Korean Photovoltaic Development Organization (KPVDO) for planning and

managing the Korea’s solar R&D program from 2004 through 2008. He is currently dean of Green School

at Korea University and is president of the Korean Photovoltaics Society (KPVS).

And so the second day of the technical program of the 7h WCPEC is done! Congratulations to all of the

award winners!