Barrier property of liquid getter-filled encapsulation for transparent organic solar cells

One of key issues of organic solar cells (OSCs) is to protect them from oxygen and moisture. The most commonly used method utilizes UV-cured epoxy along with a desiccant inside the glass-capped OSC devices. Though the conventional glass encapsulation allows high gas diffusion barrier, yet a desiccant used inside the device is opaque, which makes it difficult to fabricate a transparent OSC device. For small molecule based transparent photovoltaic devices, we come up with an advanced glass encapsulation where a liquid getter is filled. A highly transparent liquid getter is first coated on a flat encapsulation glass and UV-cured. The OSC device is then capped with the liquid getter-coated encapsulation glass using UV-cured epoxy. To demonstrate its barrier property, we have fabricated the OSC device that consists of ITO(150nm)/CuPc:C₆₀(33nm, 50 wt%)/C₆₀(10nm) /Bphen(5nm)/Al(150nm) and made a comparison with a glass encapsulated one in terms of the conversion efficiency as a function of time at temperature of 85°C and a common relative humidity of 85%. It shows that the barrier property of the liquid getter-filled encapsulation is comparable with that of the conventional glass encapsulation. Furthermore, the transparency of the liquid getter-filled encapsulation is as high as 94% at 520nm.