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Abstract A facile hydrothermal process is used to prepare hybrid graphene-MoO 3 particles to be used as hole transport layers (HTLs) in organic solar cells (OSCs). The OSCs with active layer donor/acceptor combinations of Poly[N-9″-hepta-decanyl-2,7-carbazolealt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and fullerene derivative [6,6]-phenyl-C71-butyric acid methylester (PC 71 BM) exhibit an enhanced power conversion efficiency (PCE) of 7.07%, an increase by 19% with the hybrid HTL compared to those devices with only MoO 3 HTLs. Through investigating the optical and electrical properties of the devices, we found that the superior PCE originates from an enhanced hole transport property resulting from the extraction capabilities of G-MoO 3. Comparing with thermal evaporated MoO 3 , the G-MoO 3 exhibits a higher optical transmittance, improved electrical conductivity and enhanced hole mobility. Moreover, the work function of the hybrid G-MoO 3 was close to the highest occupied molecular orbital (HOMO) level of PCDTBT, which reduced the energy barrier for the carriers and was suited for hole transport. Graphical abstract Image 1028359 Highlights • Hybrid graphene-MoO 3 (G-MoO 3) particles were synthesized via a simple hydrothermal method. • The G-MoO 3 was introduced into organic solar cells as hole transportion layers. • The organic solar cells with G-MoO 3 hole transportion layers exhibited higher conductivity and hole mobility. [ABSTRACT FROM AUTHOR]

Abstract Polymer solar cells (PSCs) suffer energy loss due to a number of reasons including high thermalisation, large exciton binding energy and electron-hole recombination within the active layer of the device. Although much effort has gone into addressing the above, interface recombination between a FTO cathode and ZnO electron transport layer (ETL) has remained relatively unnoticed. In this paper, an efficient inverted PSC is demonstrated by introducing a solution-processed SnO 2 film between the ZnO ETL and FTO cathode. The use of the SnO 2 layer, improves significantly all the device performance parameters of PSCs based on P3HT:PC 61 BM and PCDTBT:PC 71 BM system, achieving higher power conversion efficiency (PCE) up to 4.25% and 7.16%, compared to that without the SnO 2 film (PCE 3.10% and 5.52%). The improved performance is attributed to the enhanced optical transmission, the reduced energy barrier and suppression of carrier recombination at the interface between the ZnO layer and cathode. Furthermore, the SnO 2 film is shown to facilitate electron injection as well as effective hole blocking from the active layer. This study provides an efficient approach to optimize the device performance of PSCs by interfacial modification at bottom conductive electrode. Graphical abstract Image Highlights • Solution-processed SnO 2 nanoparticles were introduced to improve the electron transport in ZnO-based PSCs. • The PCE of PCDTBT: PC 71 BM-based PSCs was increased to 7.16% by incorporating the SnO 2 /ZnO bilayer interlayer. • Enhanced performance could be attributed to the reduced energy barrier and suppressed carrier recombination. [ABSTRACT FROM AUTHOR]