Simple organic molecules with permanent dipole moments -amino acids and heterocycleshave been successfully employed in bulk-heterojunction organic solar cells as interlayer between photoactive material and electron contact. A large increase of open-circuit voltage and fill factor could be observed for 4 different polymers as donor material in the photoactive layer. A combination of current-voltage curves, Scanning Kelvin-Probe AFM, ultraviolet photoelectron spectroscopy and electroluminescence measurements as well as numerical simulations were carried out to clarify in detail the underlying mechanisms. All results fully confirm the hypothesis that the main effect is an accumulation of electrons and a depletion of

We present a significant efficiency enhancement of hybrid bulk heterojunction solar cells by utilizing CdSe quantum dots attached to reduced graphene oxide (rGO) as the electron accepting phase, blended with the PCPDTBT polymer. The quantum dot attachment to rGO was achieved following a self-assembly approach, recently developed, using thiolated reduced graphene oxide (TrGO) to form a TrGO-CdSe nanocomposite. Therefore, we are able to obtain TrGO-CdSe quantum dot/PCPDTBT bulk-heterojunction hybrid solar cells with power conversion efficiencies of up to 4.2%, compared with up to 3% for CdSe quantum dot/PCPDTBT devices. The improvement is mainly due to an increase of the open-circuit voltage from 0.55 V to 0.72 V. We found evidence for a significant change in the heterojunction donor-acceptor blend nanomorphology, observable by a more vertical alignment of the TrGO-quantum dot nanocomposites in the z-direction and a different nanophase separation in the x-y direction compared to the quantum dot only containing device. Moreover, an improved charge extraction and trap state reduction were observed for TrGO containing hybrid solar cells.

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