Low band-gap CuIn(S,Se)2 thin film solar cells using molecular ink with 9.5% efficiency.

Vacuum free, solution based routes to the preparation of chalcopyrite absorbers for solar cells promise options in device design and manufacturing that are not provided by the standard vacuum based approaches. In order to fully exploit these options, the precursor should contain neither nanoparticles nor hazardous chemicals, and it should be stable under ambient conditions. In this contribution we report on CuIn(S,Se)2 thin film preparation based on spin coating of an air stable molecular ink containing metal chlorides and thiourea in organic solvents. Several key parameters directly influencing the performance of the resulting solar cells have been identified. Wetting of the glass/Mo substrate has been adjusted by varying the concentration of ethylene glycol butyl ether in the ink. Before annealing in Ar/Se at atmospheric pressure, several cycles of ink deposition and drying can be used to increase the thickness of the precursor stack. Careful balancing of ink concentration, number of precursor deposition cycles, and annealing temperature profile will transform the multi-layer precursor into a sufficiently thick, continuous, large grained film as required for high quantum efficiency, and good red response of the cells. These optimizations aimed at high photo current have already led to an efficiency of 9.5%. [ABSTRACT FROM AUTHOR]