Improvement in Solid-State Dye Sensitized Solar Cells by <i>p</i>‑Type Doping with Lewis Acid SnCl₄

The Lewis acid SnCl₄ is employed as a <i>p</i>-type dopant for 2,2′,7,7′-tetrakis­(<i>N</i>,<i>N</i>-di-<i>p</i>-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) for the solution process in solid-state dye sensitized solar cell. The UV–vis absorption spectra and time-resolved photoluminescence (PL) spectra are used to investigate the doping level of spiro-OMeTAD with a <i>p</i>-type dopant, indicating the strong molecular acceptor of SnCl₄. X-ray photoelectron spectra (XPS) exhibiting close energy shifts of the Fermi level toward HOMO are observed when adding Li salt or SnCl₄. A significant enhancement in fill factor of the photovoltaic devices, corresponding to the power conversion efficiency, is observed when doping with SnCl₄. This is attributed to the low charge transport resistance of the hole transport film and high hole injection efficiency from the hole transport material to the counter electrode

Hole-Conductor-Free Mesoscopic TiO₂/CH₃NH₃PbI₃ Heterojunction Solar Cells Based on Anatase Nanosheets and Carbon Counter Electrodes

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

Boron-Doped Graphite for High Work Function Carbon Electrode in Printable Hole-Conductor-Free Mesoscopic Perovskite Solar Cells

Work function of carbon electrodes is critical in obtaining high open-circuit voltage as well as high device performance for carbon-based perovskite solar cells. Herein, we propose a novel strategy to upshift work function of carbon electrode by incorporating boron atom into graphite lattice and employ it in printable hole-conductor-free mesoscopic perovskite solar cells. The high-work-function boron-doped carbon electrode facilitates hole extraction from perovskite as verified by photoluminescence. Meanwhile, the carbon electrode is endowed with an improved conductivity because of a higher graphitization carbon of boron-doped graphite. These advantages of the boron-doped carbon electrode result in a low charge transfer resistance at carbon/perovskite interface and an extended carrier recombination lifetime. Together with the merit of both high work function and conductivity, the power conversion efficiency of hole-conductor-free mesoscopic perovskite solar cells is increased from 12.4% for the pristine graphite electrode-based cells to 13.6% for the boron-doped graphite electrode-based cells with an enhanced open-circuit voltage and fill factor

The Influence of the Work Function of Hybrid Carbon Electrodes on Printable Mesoscopic Perovskite Solar Cells

In printable mesoscopic perovskite solar cells (PSCs), carbon electrodes play a significant role in charge extraction and transport, influencing the overall device performance. The work function and electrical conductivity of the carbon electrodes mainly affect the open-circuit voltage (<i>V</i>_OC) and series resistance (<i>R</i>_s) of the device. In this paper, we propose a hybrid carbon electrode based on a high-temperature mesoporous carbon (m-C) layer and a low-temperature highly conductive carbon (c-C) layer. The m-C layer has a high work function and large surface area and is mainly responsible for charge extraction. The c-C layer has a high conductivity and is responsible for charge transport. The work function of the m-C layer was tuned by adding different amounts of NiO, and at the same time, the conductivities of the hybrid carbon electrodes were maintained by the c-C layer. It was supposed that the increase of the work function of the carbon electrode can enhance the <i>V</i>_OC of printable mesoscopic PSCs. Here, we found the <i>V</i>_OC of the device based on hybrid carbon electrodes can be enhanced remarkably when the insulating layer has a relatively small thickness (500–1000 nm). An optimal improvement in <i>V</i>_OC of up to 90 mV could be achieved when the work function of the m-C was increased from 4.94 to 5.04 eV. When the thickness of the insulating layer was increased to ∼3000 nm, the variation of <i>V</i>_OC as the work function of m-C increased became less distinct