LAUSR

Organic conjugated molecule/silicon (Si) heterojunction has been widely investigated to build up an asymmetrical heterocontact for efficient photovoltaics. However, it is still unclear how the organic molecular structures can affect their electronic coupling interaction with Si. Here, two widely explored electron acceptors of poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (N2200) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are used to build up asymmetrical Si heterocontact to investigate their electronic coupling interaction. It is found that PCBM displays different electronic coupling with Si from N2200, which is ascribed to their various physical distance with Si based on a systematic and detailed density functional theory calculation. Organic layer incorporation not only suppresses the surface charge recombination velocity but also leads to an Ohmic contact between Si and Al. Therefore, a doping-free organic/Si heterojunction photovoltaic with a power conversion efficiency of 14.9% is achieved with PCBM layer. This work discloses a key factor affecting organic/Si electronic coupling interaction, which helps build up high quality Si heterocontact for solar cells and other optoelectronic devices. Furthermore, the simplified heterocontact achieved by a low temperature, solution processed, and lithography-free steps has a dramatic improvement on conventional diffusion doped-silicon one at high temperature.