Development of high-efficient three-layered organic solid-state solar cell

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(1) p-i-n organic solar cells having thick codeposited i-interlayer composed of metal-free phthalocyanine and fullerene were successfully fabricated by using fullerene purified seven-nine level (99.99999%) by means of the single-crystal formed sublimation. Fill factor of p-i-n cells hardly decreased even for extremely thick i-interlayer reaching 1200 nm. Short-circuit photocurrent density reached 19 mAcm^<-2> based on nearly 100% absorption of visible light in the solar spectrum by thick i-interlayer. As a result, the photo-electric conversion efficiency of 5.3% (world record) was obtained.(2) Long-term operation tests of p-i-n organic solar cells were performed in various atmosphere. Under high vacuum (<10^<-7> Torr), p-i-n cell covered with Al-doped ZnO film acting as transparent electron transport layer was operated without degradation for 1000 hours (42 days).(3) It has been confirmed that the attainable open-circuit photovoltage (V_<oc>) for organic photovoltaic cells consisting of co-deposited films is determined by the effective bandgap, namely, the energetic difference between the LUMO level of the n-type organic semiconductor and the HOMO level of the p-type organic semiconductor. The observed V_<oc> increased with increasing effective bandgap and exceeded 0.7 V.