Chlorophyll-based organic solar cells with improved power conversion efficiency

Chlorophylls（Chls）, and associated chlorophyll derivatives, are one of the oldest, most versatile organic semiconductors found in nature. Herein, we present two easily semi-synthesized chlorophyll derivatives, namely, chlorin e6 trimethyl ester（Ce6Me3） and its copper complex（Cu–Ce6 Me3）, as the p-type dopants for organic semiconductors and their impact in organic solar cells（OSCs）. In our study, both Chls showed intense Soret and Q y bands in the UV-visible spectra, leading to an effect means for capturing solar light and energy. Chls also exhibited high carrier mobility owing to the partial formation of aggregates through the spin-coating process. Using Chls, we fabricated OSCs in both planar-heterojunction（PHJ） and bulkheterojunction（BHJ） solar cell configurations, together with C70/PC70 BM as electron acceptors. In PHJ solar cells, we received solar power conversion efficiencies（PCEs） of only 0.85% and 0.93% for Cu–Ce6 Me 3-and Ce6Me3-based devices, respectively, with the thickness of the donor layer at 5 nm. In BHJ cells, we achieved much higher PCEs of 1.53% and 2.05% for Cu–Ce6Me3 :PC 70 BM and Ce6Me3 :PC 70 BM respectively, where both blending ratios were set to 1:8. The improvement on PCE in BHJ cells may be attributed to the better charge separation increase at the donor–acceptor interface.