Electric Field Distribution in Hybrid Solar Cells Comprising an Organic Donor Polymer and Amorphous Silicon

摘要

We present a study on the performance andanalysis of hybrid solar cells comprising a planar heterojunctionbetween between a conjugated donor polymer,P3HT or PCPDTBT, and hydrogenated amorphous silicon(a-Si:H). A comparison of the modeled absorption spectraof the layer stack with the measured external quantum efficiency is used to investigate the contribution of the inorganicand organic material to the photocurrent generationin the device. Although both materials contribute to thephotocurrent, the devices exhibit poor quantum efficienciesand low short circuit currents. Bandstructure simulationsof the hybrid layer structure reveal that an unfavorableelectric field distribution within the planar multilayerstructure limits the performance. Using electroabsorptionmeasurements we can show that the electric field is extremelyweakin the amorphous silicon but strong in the organicmaterial. The situation changes drasticallywhen theconjugated polymer is p-doped. Doping not only increasesthe conductivity of the organic material, but also restoresthe electric field in the amorphous silicon layer. Optimizedhybrid solar cells comprising thin doped P3HT layers exhibitenergy conversion efficiencies (ECE) up to 2.8 %.