Air-stable solution-deposited chalcopyrite CuIn1−xGaxSe2 thin film solar cells

The conversion efficiency of CIGS solar cells has reached up to a 20.3% record value [1]. It is desirable to reduce the CIGS cell cost by lowering down the manufacturing cost to enable its broader applications in the market place. Solution-based deposition offers an opportunity to fabricate CIGS thin film solar cells at a more competitive cost compared to the conventional vacuum-based process. Recently, several non-vacuum technologies, including Inkjet printing [2], electroplating [3], hydrazine [4] and nanoparticles [5], have shown great potentials to achieve comparable results with vacuum technologies. However, there are still considerable drawbacks which impede their application in a wider market field, such as the toxicity and flammability of dissolving solvents, tedious preparation process of precursor inks and fatal residuals left from organic compounds. Therefore, a versatile and controllable ink formula and an affordable deposition process are desired to fulfill the low-cost and safety requirements. In order to achieve decent conversion efficiency, the ideal chalcopyrite CIGS absorber layer should be also free of secondary phases and contaminations including binary Cu_2-xSe phase, amorphous carbon and residual from solution deposition. Herein, a novel solution-based process using low cost precursors that is capable of achieving these goals is reported.