We report on a fully integrated roll-to-roll vacuum production process of small-molecule organic p-i-n tandem solar cells. The solar foils are prepared on a flexible PET substrate. Three different laser processes were developed to pattern the transparent bottom contact, the organic layers and the metal top contact. For the ramp up phase of the production tool, a simplified organic stack was developed to reach efficiencies above 5% with moderate complexity. The modules from Heliatek’s roll-to-roll production show efficiencies of up to 6.8% on the active area of 1033cm2 with a fill factor of 65.4%. Lab modules with the same layer stack on smaller samples prepared in a batch to batch process reach about the same values in all electrical parameters proving the excellent scalability of small-molecule p-i-n tandem solar cells prepared by vacuum deposition.
Thin metal films are a desirable alternative to indium tin oxide for utilization in organic solar cells (OSC).We
describe background and processing parameters for thin metal films and show examples of top-illuminated
OSC employing metal electrodes. Simulations are introduced as tool for OSC fabrication; several pitfalls
are presented which must be considered for successful numerical treatment of thin-film layers at coalescence
thicknesses and for coherent treatment.
The transparent electron transport material NTCDA (1,4,5,8-naphthalenetetracarboxylic dianhydride) was examined
in order to find a suitable substitute for C60 which is today often used in small molecular organic solar
cells as transport layer. Due to its wide band gap, NTCDA does not absorb in the visible range and is furthermore
exciton blocking. By doping with AOB (acridine orange base), its conductivity was raised to about
1 • 10-4S/cm. It can therefore simultaneously be used as electron transport material and optical spacer in p-i-n
type solar cells, leading to power conversion efficiencies of up to 2.83%. Additionally, an investigation of the
surface morphology using AFM was performed.