Solution-processed environmentally friendly Ag2S colloidal quantum dot solar cells with broad spectral absorption

A facile heat-up synthesis route is used to synthesize environmentally friendly Ag2S colloidal quantum dots (CQDs) that are applied as light absorbing material in solid state p-i-n junction solar cell devices. The as-synthesized Ag2S CQDs have an average size of around 3.5 nm and exhibit broad light absorption covering ultraviolet, visible, and near infrared wavelength regions. The solar cell devices are constructed with a device architecture of FTO/TiO2/Ag2S CQDs/hole transport material (HTM) /Au using a solution-processed approach. Different HTMs, N2,N2,N2',N2',N7,N7,N7',N7'-octakis(4-methoxyphenyl)-9,9'-spirobi(9H-fluorene)-2,2',7,7' tetramine (spiro-MeOTAD), poly(3-hexylthiophene-2,5-diyl) (P3HT), and poly((2,3-bis(3-octyloxyphenyl)-5,8-quinoxalinediyl)-2,5-thiophenediyl) TQ1 are studied for maximizing the device photovoltaic performance. The solar cell device with P3HT as a hole transport material gives the highest performance and the solar cell exhibit broad spectral absorption. These results indicate that Ag2S CQD have high potential for utilization as environmentally friendly light absorbing materials for solar cell application and that the hole transport material is critical to maximize the solar cell photovoltaic performance.