Polarizing Organic Photovoltaics

Today’s most prevalent information display technology is the liquid crystal display (LCD). Unfortunately, LCDs are energy ineffi cient, as most of the backlight energy (around 75%) is lost to the orthogonal polarizers. Here, we demonstrate a novel energy recycling concept called polarizing organic photovoltaics (ZOPVs), which can potentially boost the function of an LCD by working simultaneously as a polarizer, a photovoltaic device and an ambient light or sunlight photovoltaic panel. The ZOPV fi lm was created by the uniaxial orientation of an organic conjugated polymer. A novel inverted quasibilayer structure was used to produce ZOPV devices. Signifi cant anisotropic optical and photovoltaic effects were obtained, indicating the great potential of ZOPV as a promising green technology. As an electromagnetic wave (EM), light can be divided into two linear oscillation components: the parallel (//) and perpendicular (⊥) polarizations. [ 1 ] They can be separated by a linear polarizer to provide linear polarized light, [ 2 ] and have vast applications. One of the most prevalent applications is for LCD technology. [ 3 ] Figure 1 a shows schematically the construction of LCD panels. The fundamental principle underpinning LCD operation is the modulation of light using a combination of two orthogonal polarizers with liquid crystal molecules between these two polarizers to form light valves. Currently, the most commonly used linear polarizer is the absorptive polarizer, which absorbs and wastes the unwanted polarization component while allowing the other component to be transmitted. From an energy point of view, these absorptive polarizers in LCDs are rather ineffi cient as far as the usage of the backlight photons is concerned. The power consumption of the backlight units takes up approximately 80–90% of the total power consumption in LCD modules. [ 4 ] Unfortunately, most of the backlight energy is lost to these absorptive polarizers (75%). This loss is at a maximum when the pixel displays the color black (this is when the polarizers are completely crossed), since the backlight is still fully on. In this work, we innovate on the biggest energy loss component, the polarizers, by turning the polarizer into an energy-generating photovoltaic (PV) unit, creating a polarizing organic photovoltaic device (we use the acronym ZOPV in this manuscript rather than POPV, which is often used to refer to polymer organic photovoltaics). A unique advantage of the organic conjugated materials is that the molecular chains can be easily oriented, leading to anisotropic response to polarized incident light. [ 5–8 ] This feature makes organic PV systems superior to inorganic PV or organic-hybrid PV systems [ 9 ] for the purpose of polarizing PV. ZOPV devices integrated into an LCD panel (Figure 1 b) have three potential benefi ts: i) polarization, whereby the EM wave component with an electric fi eld perpendicular to the oriented molecular chain ( s -mode polarized light [ 7 ] ) propagates through the fi lm without absorption, serving its conventional role in LCDs; ii) as a PV device, the ZOPV fi lm harvests the EM wave component parallel to the molecular chain orientation ( p -mode polarized light, which is absorbed and wasted in a conventional LCD), converting it into electricity; and iii) ambient light or sunlight PV panel, when the ZOPV device is integrated into the LCD panel, its photovoltaic function remains even when the LCD panel is not in use, producing electricity through conversion of photons from ambient light or sunlight. [ 10 ]