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 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 POCl
3
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 PbX
3
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 CsPbBr
3
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 H
2
SO
4
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 ([Fe
i
]) by more than 3 orders of magnitude. [Fe
i
] 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)PbI
3
and (MA,FA)PbI
3
. 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.
