A hole-conductor-free fully printable mesoscopic TiO2/CH3NH3PbI3 heterojunction solar cell was developed with TiO2 nanosheets containing high levels of exposed (001) facets. The solar cell embodiment employed a double layer of mesoporous TiO2 and ZrO2 as a scaffold infiltrated by perovskite as a light harvester. No hole conductor or Au reflector was employed. Instead, the back contact was simply a printable carbon layer. The perovskite was infiltrated from solution through the porous carbon layer. The high reactivity of (001) facets in TiO2 nanosheets improved the interfacial properties between the perovskite and the electron collector. As a result, photoelectric conversion efficiency of up to 10.64% was obtained with the hole-conductor-free fully printable mesoscopic TiO2/CH3NH3PbI3 heterojunction solar cell. The advantages of fully printable technology and the use of low-cost carbon-materials-based counter electrode and hole-conductor-free structure provide this design a promising prospect to approach low-cost photovoltaic devices.

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Photovoltaic solar cells based on organic−inorganic hybrid halide perovskites have achieved a substantial breakthrough via advanced interface engineering. Reports have emphasized that combining the hybrid perovskites with the Lewis base and/or graphene can definitely improve the performance through surface trap passivation and band alignment alteration; the underlying mechanisms are not yet fully understood. Here, using density functional theory calculations, we show that upon the formation of CH 3 NH 3 PbI 3 interfaces with three different Lewis base molecules and graphene, the binding strength with S-donors thiocarbamide and thioacetamide is higher than with O-donor dimethyl sulfoxide, while the interface dipole and work function reduction tend to increase from S-donors to O-donor. We provide evidences of deep trap state elimination in the S-donor perovskite interfaces through the analysis of defect formation on the CH 3 NH 3 PbI 3 (110) surface and of stability enhancement by estimation of activation barriers for vacancy-mediated iodine atom migrations. These theoretical predictions are in line with the experimental observation of performance enhancement in the perovskites prepared using thiocarbamide.

Compared to the DSSCs based on WH-C1 and YD20 with short alkyl chains, the device sensitized by WH-C2 with the hexyloxy group shows a significantly enhanced Voc, Jsc and power conversion efficiency (η).