Cost-effective hollow honeycomb textured back reflector for flexible thin film solar cells

• Hollow-HSHT nanostructure have been prepared under a cost-effective approach.
• Numerical simulations show high efficient photonic resonance through the hollow-HSHT nanostructure.
• Experimental measurements show effective resonant light scattering.
• Both the simulated and measured EQE curves are enhanced.
• High efficient a-Si:H solar cell is obtained showing its good potential as flexible back reflector.

We demonstrate an effective light trapping back reflector (BR) for flexible thin-film solar cells (TFSCs) that is composed of self-ordered flexible nanoporous anodic aluminum oxide (np-AAO) with hollow hexagonally-symmetric honeycomb textures (hollow-HSHT) under a cost-effective anodic oxidation approach. The dielectric nano-scatters are well compatible with nearly all types of TFSCs, including cells produced using high temperature processes. The performance of the hollow-HSHT nanostructure were investigated both experimentally and theoretically. The enhanced diffraction behavior, guided resonance and light absorption were identified through finite-difference-time-domain (FDTD) simulation. A highly conductive AZO film was deposited on the hollow-HSHT as a back electric contact for making solar cells. As a result, the flexible and periodic hollow-HSHT based BR yielded an efficiency of 8.3% for thin-film a-Si:H solar cell, which is much higher than the efficiency of 6.7% for the reference cell on the flat AZO back contact. Furthermore, the hollow-HSHT based BR provides a means of enhancing absorption in whole wavelength range, thus opening an approach for creating high-efficiency, low cost flexible TFSCs.