Schaefer, S.; Albrecht, S.; Neher, D.; Schulze, T.; Conrad, E.; Korte, L.; Rech, B.; Wördenweber, J; Gordijn, A; Scherf, U; Dumsch, I: Electric Field Distribution in Hybrid Solar Cells Containing Amorphous Silicon and Polymers. Organic Photonics and Photovoltaics 2 (2014), p. 12-20
We present a study on the performance and analysis of hybrid solar cells comprising a planar heterojunction between between a conjugated donor polymer, P3HT or PCPDTBT, and hydrogenated amorphous silicon (a-Si:H). A comparison of the modeled absorption spectra of the layer stack with the measured external quantum efficiency is used to investigate the contribution of the inorganic and organic material to the photocurrent generation in the device. Although both materials contribute to the photocurrent, the devices exhibit poor quantum efficiencies and low short circuit currents. Bandstructure simulations of the hybrid layer structure reveal that an unfavorable electric field distribution within the planar multilayer structure limits the performance. Using electroabsorption measurements we can show that the electric field is extremelyweak in the amorphous silicon but strong in the organic material. The situation changes drasticallywhen the conjugated polymer is p-doped. Doping not only increases the conductivity of the organic material, but also restores the electric field in the amorphous silicon layer. Optimized hybrid solar cells comprising thin doped P3HT layers exhibit energy conversion efficiencies (ECE) up to 2.8 %.