Abstract

Aligned silicon nanowire (SiNW) arrays that bare the potential for efficiencies >15% are fabricated on multi-crystalline silicon (mc-Si) layers on glass using reactive ion etching (RIE) with lithographic large area nano-patterning using densely packed polystyrene (PS) spheres. Diameter, length, density and shape of SiNWs can be tuned for highest absorptions (close to 90%) and as small as possible surface areas, since surfaces are prone to carrier recombination since passivation or functionalization is usually never perfect. Various SiNW cell concepts are presented: (i) a hybrid organic/inorganic cell with SiNW-based absorber and a hole conducting polymer (PEDOT:PSS - encapsulation procedures for long term stability suggested); (ii) a semiconductor-insulator-semiconductor (SIS) cell with SiNW absorber, oxide (few Å Al₂O₃ by atomic layer deposition-ALD) ) tunneling barriers for charge carrier separation and a transparent conductive oxide (TCO – here: Al:ZnO, by ALD). Initial thin film solar cell prototypes reached open-circuit voltages of > 630 mV, short-circuit current densities of even ~ 30 mA/cm² and efficiencies >13%. Correlated microscopies / spectroscopies are used to improve materials / cells: (i) electron beam induced current (EBIC) – to study charge carrier distributions in nano-architectures; (ii) electron backscatter diffraction (EBSD) – to study structural quality of the multi-crystalline Si layer before and after patterning; (iii) integrating sphere measurements, external quantum efficiency, photo- and cathode-luminescence – to study optical properties and (iv) 4-point nano-probing of individual NWs – to study electrical properties. Novel electrodes (e.g. graphene, silver nanowire webs) to further improve the cells are evaluated.

© 2015 Optical Society of America