Abstract :
Historically, the design of hybrid solar photovoltaic thermal (PVT) systems has focused on cooling crystalline silicon (c-Si)-based photovoltaic
(PV) devices to avoid temperature-related losses. This approach neglects the associated performance losses in the thermal system
and leads to a decrease in the overall exergy of the system. Consequently, this paper explores the use of hydrogenated amorphous
silicon (a-Si:H) as an absorber material for PVT in an effort to maintain higher and more favorable operating temperatures for the thermal
system. Amorphous silicon not only has a smaller temperature coefficient than c-Si, but also can display improved PV performance
over extended periods of higher temperatures by annealing out defect states from the Staebler–Wronski effect. In order to determine the
potential improvements in a-Si:H PV performance associated with increased thicknesses of the i-layers made possible by higher operating
temperatures, a-Si:H PV cells were tested under 1 sun illumination (AM1.5) at temperatures of 25 C (STC), 50 C (representative PV
operating conditions), and 90 C (representative PVT operating conditions). PV cells with an i-layer thicknesses of 420, 630 and 840 nm
were evaluated at each temperature. Results show that operating a-Si:H-based PV at 90 C, with thicker i-layers than the cells currently
used in commercial production, provided a greater power output compared to the thinner cells operating at either PV or PVT operating
temperatures. These results indicate that incorporating a-Si:H as the absorber material in a PVT system can improve the thermal performance,
while simultaneously improving the electrical performance of a-Si:H-based PV.
2012 Elsevier Ltd. All rights reserved
