Capacitance–voltage characteristics of P3HT:PCBM bulk heterojunction solar cells with ohmic contacts and the impact of single walled carbon nanotubes on them

• Published in: Organic electronics Vol. 13; no. 7; pp. 1158 - 1165
• Main Authors: Mallajosyula, Arun Tej, Sundar Kumar Iyer, S., Mazhari, Baquer
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.07.2012; Elsevier
• Subjects: Applied sciences; Carbon nanotubes; Charge transport; Compound structure devices; Conjugated polymers; Electronics; Energy; Exact sciences and technology; Interfaces; Natural energy; Negative capacitance; Optoelectronic devices; Photovoltaic conversion; Photovoltaic devices; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Solar cells. Photoelectrochemical cells; Solar energy; Carbon nanotubes; Conjugated polymers; Charge transport; Photovoltaic devices; Negative capacitance; Performance evaluation; Free field; Frequency dependence; Ohmic contact; Fullerene compounds; Low frequency; Energy level; Butyric acid; Photovoltaic cell; Ester; Conjugated polymer; Space charge limited conduction; Thiophene derivative polymer; Optoelectronic device; Current density; Voltage capacity curve; Heterojunction; Interface state; Trap; Solar cell; Thickness; Singlewalled nanotube; Capacitance
• ISSN: 1566-1199; 1878-5530
• DOI: 10.1016/j.orgel.2012.03.018

[Display omitted] . ► Large conductance and non-linearity with SWNTs causes NC in reverse bias. ► NC has contributions from two processes. ► SWNTs affect 2nd order process. ► Non-monotonous variation in NC due to charge injection process. ► Onset frequency of NC need not have direct relation with mobility. Capacitance–voltage (C–V) characteristics of P3HT:PCBM devices of two different thicknesses are correlated with current density–voltage (J–V) characteristics. The rising portion of the C–V characteristics coincides with the exponential current density below the built-in voltage. The negative capacitance (NC) of these devices is a low frequency phenomenon and it occurs in trap-free space charge limited current (SCLC) regime. The onset frequencies of NC for devices with and without SWNTs also do not follow direct relation with effective mobility. The NC in thin devices has non-monotonic change with voltage for thin devices showing that interface state kinetics can be the reason for its occurrence. The NC of thick devices, on the other hand, increases monotonically with voltage showing that bulk properties dominate in these. Addition of SWNTs to these devices for efficiency improvement does not modify their built-in voltage. Also, the SWNTs do not affect the forward NC behaviour. However, the devices containing SWNTs show NC in reverse bias also which has different frequency dependence with voltage. The reverse bias NC is attributed to the large non-linear reverse current by charge injection into the additional energy levels introduced by SWNTs.