The role of photon energy in free charge generation in bulk heterojunction solar cells

D. Di Nuzzo, L.J.A. Koster, V.S. Gevaerts, S.C.J. Meskers, R.A.J. Janssen

Research output: Contribution to journalArticlepeer-review

12 Citations (SciVal)


To determine the role of photon energy on charge generation in bulk heterojunction solar cells, the bias voltage dependence of photocurrent for excitation with photon energies below and above the optical band gap is investigated in two structurally related polymer solar cells. Charges generated in (poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b'']dithiophene)-alt-4,7-(2,1,3-benzothia-diazole)] (C-PCPDTBT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) solar cells via excitation of the low-energy charge transfer (CT) state, situated below the optical band gap, need more voltage to be extracted than charges generated with excitation above the optical band gap. This indicates a lower effective binding energy of the photogenerated electrons and holes when the excitation is above the optical band gap than when excitation is to the bottom of the CT state. In blends of PCBM with the silicon-analogue, poly[(4,4-bis(2-ethylhexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (Si-PCPDTBT), there is no effect of the photon energy on the electric field dependence of the dissociation efficiency of the CT state. C-PCPDTBT and Si-PCPDTBT have very similar electronic properties, but their blends with PCBM differ in the nanoscale phase separation. The morphology is coarser and more crystalline in Si-PCPDTBT:PCBM blends. The results demonstrate that the nanomorphological properties of the bulk heterojunction are important for determining the effective binding energy in the generation of free charges at the heterojunction.
Original languageEnglish
JournalAdvanced Energy Materials
Issue number18
Early online date4 Aug 2014
Publication statusPublished - 29 Dec 2014


Dive into the research topics of 'The role of photon energy in free charge generation in bulk heterojunction solar cells'. Together they form a unique fingerprint.

Cite this