An environmentally compatible organic solar cell (OSC) has potential to build a global clean energy infrastructure for the world. However, much less attention has been focused on the structures sourced from greener origins to enhance the sustainability aspect of these devices. Herein, we report a rational design, synthesis, and characterization of donor (D)-acceptor (A)based green organic small molecules, consisting of difluoro-2,1,3benzothiadiazole (BTF 2 ) as the acceptor, with thiophene (T) and renewable resource materials, cardanol (C) and guaiacol (G) as the donor materials. The reference molecule, abbreviated as T 4 BTF 2 , is fully petro-sourced, while C 2 T 2 BTF 2 and G 2 T 2 BTF 2 are partly renewable origin molecules. Broad and strong absorption characteristics ranging from 300 to 600 nm along with high thermal stability are supportive for utility of the green origin small molecules in solar cells. Density functional theory (DFT) calculations revealed that G 2 T 2 BTF 2 is more highly planar than C 2 T 2 BTF 2 due to the difference in the positioning of the alkyl/alkoxy chain. With bulk heterojunction OSCs with PC 71 BM as the acceptor, G 2 T 2 BTF 2 exhibited a high V oc of 0.83 V among all the analyzed small molecules. When compared with the reference molecule T 4 BTF 2 , G 2 T 2 BTF 2 showed a high PCE of 5.56% with a high J sc of 10.98 mA/cm 2 and FF of 0.61, whereas the PCEs of T 4 BTF 2 and C 2 T 2 BTF 2 are 3.98% and 3.23%, respectively. Our work demonstrates a rational approach to synthesize and develop green organic semiconductors using the biofeedstock derived starting materials for realizing efficient and environment compatible OSCs.

Recently, the ternary active‐layer‐based organic solar cells have shown remarkable increment in the power conversion efficiency (PCE) by utilizing the synergistic effect of complementary absorption, band alignment, and nano‐scale morphology enhancement. Non‐fullerene acceptors (NFAs) are an important class of functional materials for the improved performance of ternary organic solar cells due to their role in improvising the light absorption and the morphology of the active layer. Here, the non‐fullerene (NF) molecule, NAI‐FN‐NAI (BO), is used as the third component in the bulk heterojunction of PTB7‐Th: PC71BM to fabricate the ternary organic solar cell. The magical number of the composition, i.e., 20% by weight of the NF in the ternary active layer resulted in the PCE of 8.1% devices, which is almost 35% higher efficiency than PTB7‐Th: PC71BM binary devices having the PCE of 6%. The enhanced efficiency is observed even though the lessened effect of complementary absorption and band alignment factors of the NF. Such an improved efficiency is attributed in ternary devices to the nano‐scale morphology enhancement. It could pave the way to realize the best possible bulk heterojunction blend to attain high PCE close to inorganic counterparts.

In inverted structure-based semitransparent organic solar cells (OSCs), the electron transport layer (ETL) plays a crucial role in the improvement of the transparent cathode efficiency in collecting and extracting negative charge carriers. Zinc oxide (ZnO) thin film prepared by zinc acetate dihydrate precursor with various benefits is generally used as ETL. However, high temperature, less charge transfer ability, and irregular film surface due to fiber-like domain formation limit the device performance. In this work, a new approach is presented by using low-temperature processed polyethylenimine ethoxylated (PEIE) as ETL in semitransparent OSCs fabricated in an ambient environment with a blend of low-bandgap donor polymer PTB7-Th, and fullerene acceptor, PC71BM, based active layer. For semitransparent OSCs, the thickness of the silver electrode has been varied from 55 nm to 25 nm to investigate its effect on the electrical and optical properties of the devices. The power conversion efficiencies (PCE) of 5.1% and 4.6% were achieved for semitransparent devices (25 nm thickness of silver electrode) for PEIE and ZnO ETLs, respectively. Similarly, PCE of 7% and 6.7% have been achieved for opaque devices (85 nm thickness of silver electrode) using PEIE and ZnO ETLs, respectively. PEIE based devices with 25 nm Ag demonstrate about 25-30% transparency. The impedance spectroscopy measurements indicate low interfacial contact resistance and fast charge transfer capability for PEIE interlayer-based devices compared to the ZnO based devices. The encapsulated semitransparent devices processed and stored in ambient condition with PEIE and ZnO ETLs were found to retain ∽80% performance for up to 45 days.