Advances in Photovoltaics is an annual one day conference focussing on the current state of the art in photovoltaics and the challenges that must be overcome, pulling speakers from academia, industry and government. This year’s event was held at Loughborough University but will return to London next year after the Institute of Physics moves to its new home near Kings Cross.

Bill Tumas, Associate Director of the National Renewable Energy Laboratory (NREL) in the United States, was the first speaker giving an overview of recent advances in photovoltaics and the remaining challenges. With the omnipresent NREL efficiency chart, Bill showed recent advances in multiple PV materials, but cautioned that just as the motor car didn’t stop at horse-parity, photovoltaics shouldn’t be content with reaching grid-parity, but must continue to improve…’the job ain’t done yet’. As Solar approaches grid-parity, the energy infrastructure must be modernised and expanded to handle the increasing electrical demand associated with vehicle electrification.   In order to meet this rising demand, high throughput manufacturing of solar cells involving roll to roll processing of flexible thin films will be necessary, instead of the slow and high energy processing of crystalline silicon panels. Bill also spoke of the need for alternative uses of solar energy, such as photoelectrochemical splitting, which produces energy dense fuels from sunlight. Additionally, Bill spoke about the challenges of recycling modules, including the economic feasibility of recycling materials 25 years in the future.

Tim Silverman also of NREL, and a visiting academic at Loughborough University, gave a lively talk about module performance and reliability. The use of sub-bandgap mirrors and reflective back surfaces have been utilised by NREL to lower the operating temperature of ground mounted PV, leading to real-world efficiency gains. Tim provided an interesting look at the philosophy of failure testing, and how much uncertainty still remains in the methods used. He then covered the threat posed to panels by seemingly innocuous shadows, including renditions of photos of workers inadvertently casting damaging shadows in solar panel factories. Scanning electron microscopy and electroluminescence was used to identify the shunts caused by these shadows and the microfractures caused by mechanical forces on silicon panels.

Will Hitchcock, founder and managing director of Above Surveying Ltd highlighted the problems occurring in many UK utility scale solar installations. Above Surveying use drones equipped with thermographic cameras to rapidly and thoroughly assess the health of PV assets in the field, providing site managers with a detailed assessment of faults and the modules affected. This analysis is both quicker and provides a more in-depth appraisal than ground based methods, showing managers when solar cells, junction boxes and wiring (and even modules) require replacing. The technique can also appraise the effects of soiling and the effectiveness of cleaning.  Above Surveying is a leader in its field addressing the important issues of operations and maintenance with automated aerial surveillance and state of the art computing and image analysis.

Colin Wolden of the Colorado School of Mines presented a 40 year history that took CdTe solar cells from a fledgling technology to almost 20GW of installed capacity. The talk finished with an insight into the next innovations that promise to contribute to the NREL champion efficiency chart.

Tom Fiducia of Loughborough University presented a detailed analysis using cathodoluminescence and SIMS to examine the latest CdTe technology that incorporates Se into an alloy at the front of the absorber. Interdiffusion occurs following the CdCl2 activation treatment to provide grading of the Se.  A 3-dimensional reconstruction was used to show the location of Cl and Se in the CdSeTe device to explain in detail the mechanisms leading to high conversion efficiency.

Patrick Isherwood gave an insightful look at alternative TCOs that could be used to relieve the industry’s reliance on ITO, with a focus on the use of non-toxic Earth abundant materials and p-type TCOs, and the issues currently plaguing them, were also broached.

Liam Welch

CREST Doctoral Researcher

September 2018