Addition of a small fraction of high boiling point solvent into the host of donor/acceptor blend is one the best approach to control the morphology in order to enhance the power conversion efficiency of organic bulk heterojunction (BHJ) solar cell devices. Herein, we focus on the effect of two thiol-based additives (1,6-hexanedithiol (HDT) and 1,5-pentanedithiol (PDT)) on the charge dynamics of P3HT:PCBM blend system, studied by transient absorption spectroscopy (TAS) and correlated with the solar cell device performance. TAS reveals a more efficient charge generation and polaron formation in the systems with additives as compared to those without (NA systems), at the onset which persists up to few microseconds. The recombination dynamics also exhibits the reduced recombination losses on adding these additives in this system; however, there is marginal change of recombination dynamics in PDT added system with the control. These charge dynamics were validated using the analytical model proposed in our previous work and also correlated with improved device performance (ηNA = 0.9%, ηHDT = 2.7%, ηPDT = 1.6%).
The blending of metallic nanoparticles into the active layer of organic solar cells in a bid to enhance their light
absorption and device performance has led to controversial reports of both efficiency enhancement and degradation.
Herein, through comprehensive transient absorption spectroscopy, we present clear evidence of traps being responsible
for performance degradation of poly (3-hexylthiophene): [6,6]-phenyl-C 61-butyric acid methyl ester organic
photovoltaic devices incorporated with oleylamine-capped silver nanoparticles. Although the presence of the metallic
nanoparticles leads to more excitons being generated in the active layer, higher losses suffered by the polaron population
through trap-assisted recombination strongly limits the device performance. Device modeling based on a single mid-gap
trap state introduced by the AgNPs can well reproduce the current-voltage curves of the plasmonic organic solar cells –
in agreement with the transient absorption findings. These new insights into the photophysics and charge dynamics of
plasmonic organic solar cells would help resolve the existing controversy and provide clear guidelines for device design