Photoconduction in Amorphous Organic Solids

Abstract

Herein, we focus on the principles of photoconduction in random semiconductors—the key processes being optical generation of charge carriers and their subsequent transport. This is not an overview of the current work in this area, but rather a highlight of elementary processes, their involvement in modern devices and a summary of recent developments and achievements. Experimental results and models are discussed briefly to visualize the mechanism of optical charge generation in pure and doped organic solids. We show current limits of models based on the Onsager theory of charge generation. After the introduction of experimental techniques to characterize charge transport, the hopping concept for transport in organic semiconductors is outlined. The peculiarities of the transport of excitons and charges in disorderd organic semiconductors are highlighted. Finally, a short discussion of ultrafast transport and single chain transport completes the review.

Structural correlations in the generation of polaron pairs in low-bandgap polymers for photovoltaics

“…This polymer shows the longest polaron pair decay ( > 12 ps) among the studied samples. Here, polaron pair formation is driven by exciton delocalization at sites with energetic disorder (typically > 50 meV) 42 . A recent work by Reid et al 43 shows that the polaron yield in P3HT depends on the degree of crystallinity because the charge separation might occur at the interface between the crystalline and amorphous regions.…”

Organic solar cells with plasmonic layers formed by laser nanofabrication

“…In addition, the strong local electric field can enhance the exciton dissociation in the active layer, a concept which has been proven experimentally at other studies. [32][33][34] On the contrary, in dense particle films the absorption of previous studies. 35,36 The lower PL quenching can be attributed to the strong local electric field at the particles' vicinity which promotes the exciton dissociation.…”

“…35,36 The lower PL quenching can be attributed to the strong local electric field at the particles' vicinity which promotes the exciton dissociation. [32][33][34] Furthermore, the high density of particles with small separation distances causes an extra shadowing effect, undesirable for high efficiency photovoltaics.…”

Integration of electro-active π-conjugated units in nanosegregated liquid-crystalline phases

“…46 The charge carrier mobility determined by the time-of-flight method is a drift mobility affected by disorder and defects. 47 The measurement of the carrier mobility over wide ranges of temperatures and fields can provide information on the carrier transport mechanism in organic semiconductors. Conventional LC semiconductors exhibit LC phases within narrow, elevated temperature ranges.…”

“…The dependence on the electric field and the temperature can be described by the Gaussian disorder model, which has been used for the analysis of carrier transport characteristics in organic amorphous semiconductors. 47 The field-and temperature-dependence of the electron mobility was analyzed based on a one-dimensional disorder model. 48 In this model, carrier mobility μ is described by equation (1), where T is the temperature, F is the electric field, σ is the energetic disorder, Σ is the positional disorder and C is a constant.…”