Effects on amorphous silicon photovoltaic performance from high-temperature annealing pulses in photovoltaic thermal hybrid devices

There is a renewed interest in photovoltaic solar thermal (PVT) hybrid systems, which harvest solar energy for heat and electricity. Typically, a main focus of a PVT system is to cool the photovoltaic (PV) cells to improve the electrical performance; however, this causes the thermal component to under-perform compared to a solar thermal collector. The low temperature coefficients of amorphous silicon (a-Si:H) allow the PV cells to be operated at high temperatures, which are a potential candidate for a more symbiotic PVT system. The fundamental challenge of a-Si:H PV is light-induced degradation known as the Staebler–Wronski effect (SWE). Fortunately, SWE is reversible and the a-Si:H PV efficiency can be returned to its initial state if the cell is annealed. Thus an opportunity exists to deposit a-Si:H directly on the solar thermal absorber plate where the cells could reach the high temperatures required for annealing.In this study, this opportunity is explored experimentally. First a-Si:H PV cells were annealed for 1 h at 100 °C on a 12 h cycle and for the remaining time the cells were degraded at 50 °C in order to simulate stagnation of a PVT system for 1 h once a day. It was found when comparing the cells after stabilization at normal 50 °C degradation that this annealing sequence resulted in a 10.6% energy gain when compared to a cell that was only degraded at 50 °C.

► Photovoltaic solar thermal (PVT) hybrid systems harvest heat and electricity.
► Amorphous silicon (a-Si:H) PV was investigated as an absorber in PVT systems.
► a-Si:H PV cells were annealed for 1 h at 100 °C on a 12 h cycle.
► This simulated stagnation of a PVT system.
► This annealing sequence resulted in 10.6% energy gain over normal PV degraded at 50 °C.