Organic Solar Cells Based on the Aggregate of Synthetic Chlorophyll Derivative with over 5% Efficiency

The power conversion efficiency (PCE) of chlorophyll (Chl)‐based organic solar cells (OSCs) is generally about 2%. Herein, a Chl‐ a derivative (CHL) and [6,6]‐phenyl‐C 71 ‐butyric acid methyl ester (PC 71 BM) are successfully used to fabricate Chl‐based OSCs with PCE over 5%. Two different preparation methods are used to prepare the active layer: 1) two‐step spin‐coating the self‐aggregated CHL and PC 71 BM solutions sequentially and 2) one‐step spin‐coating the solution of CHL:PC 71 BM blends, forming the “bilayer” (BL) and traditional bulk heterojunction (BHJ) configurations, respectively. Based on the aforementioned two kinds of active‐layer preparation methods, both inverted and regular types of OSCs are successfully investigated. All four types of devices work normally, which is likely due to the ambipolar characteristics of the CHL aggregate. Unexpectedly, the BL‐based devices yield PCEs of 5.17% for the regular type and 5.19% for the inverted type, which are higher than those of the BHJ‐based devices (3.96% for the regular type and 3.50% for the inverted type). The main improvement in PCEs of BL‐based devices comes from the enhanced short‐circuit currents, which is due to the decreased charge transfer resistance and enlarged photocurrent contribution of PC 71 BM as well as slightly enhanced electron and hole mobilities.