Triazabicylodecene can effectively n-dope a variety of organic semiconductors, including PCBM, thus increasing in-plane conductivities. We synthesized a series of TBD-based n-dopants via an N-alkylation reaction and studied the effect of various alkyl chains on the physical and device properties of the dopants. Combining two TBD moieties on a long alky chain gave a solid dopant, 2TBD-C10, with high thermal stability above 250° C. PCBM films doped by 2TBD-C10 were the most tolerant to thermal annealing and reached in-plane conductivities of 6.5×10−2 S/cm. Furthermore, incorporating 2TBD-C10 doped PCBM as the electron transport layer (ETL) in methylammonium lead triiodide (MAPbI3) based photovoltaics led to a 23% increase in performance, from 11.8% to 14.5% PCE.