Community Research and Development Information Service - CORDIS

Thin film solar cells, based on non-toxic, abundant and air-stable silicon (Si) will probably, based on forecasts, dominate the photovoltaic market in the future and thus replace bulk Si from its leading position. This prognosis is fostered by the strong cost reduction potential due to highly effective materials utilization at low energy consumption. However, thin film Si suffers from inherently small grains, which limits efficiencies to ~10% due to carrier recombination at grain boundaries.

A radical innovation of the Si thin film materials synthesis route is needed to circumvent this problem. ROD_SOL aims at the synthesis of Si nano-rods, densely packed at sufficiently large diameters (few 100 nm's) and lengths (>1µm for sufficient carrier absorption in indirect semiconductors) directly on cheap substrates like glass or flexible metal foils. The idea is to grow Si nano-rods from the gas phase that are inherently defect free, with a wrapped around pn-junction that bares the potential to decouple absorption of light from charge transport by allowing lateral diffusion of minority carriers to the pn-junction, which is at most a few hundred nm away, rather than a few µm as in conventional thin film solar cells. That way, efficiencies as in bulk Si are expectable, however, with the advantage that the 'nano-rod carpet' layer, is at most a few µm thick. A 'nano-rod carpet' that thin shows a strongly increased optical absorption.

Thus, the 'nano-rod carpet' is not only the active solar cell element but at the same time its own light trapping structure. For synthesis of the nano-rods, development of suitable contact materials and characterization of physical and structural properties four experienced research institutes have joined forces. Despite the fundamental materials research to be in focus, three companies joined the consortium to directly test and implement the novel materials and processes in a well proven, industrially viable thin film solar cell concept.