Dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (HBPDA) is a dianhydride building block with a flexible bicyclohexyl core. The polyimides synthesized form dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride are often transparent, because of the flexible polymer backbones. Thus, it can be used as shielding layers in photovoltaics. The refractive index of the polyimides can be tuned by TiO2 fillers for matching the ZnO layer (the electron transport layer), to reduce the reflection losses at the ZnO interface.
