Over the past five years, the rapid emergence of a new class of solar cell based on mixed organic–inorganic halide perovskite semiconductors has captured the attention of scientists and researchers in the field of energy conversion. Benefiting from the optimization of perovskite film deposition approaches, the design of new material systems, and the diversity of device concepts, the efficiency of perovskite solar cells (PSCs) has increased from 2.19% in 2006 to a certified 20.1% in 2014, making this the fastest-advancing solar cell technology to date. However, as a photovoltaic technology, which needs to meet the requirements of working under long-term sunlight, PSCs suffer stability concerns for both materials and devices. Evolved from dye-sensitized solar cells (DSSCs), PSCs usually contain a mesoporous electron transporting layer or scaffold layer, a perovskite active layer, a hole transporting layer and a back contact to construct a mesoscopic-structured device. Using interface engineering, mesoscopic PSCs (MPSCs) have obtained exciting stability with a hole-conductor-free printable triple-layer architecture or conventional heterojunction version. Herein, the achievements of mesoscopic solar cells from solid-state DSSCs to MPSCs are outlined and summary of recent progress in the stability of MPSCs is presented. Possible degradation mechanism and solutions are presented and, finally, challenges for the commercialization of this photovoltaic technology are discussed.

A new class of organic sulfide mediators with programmable redox properties is designed via density functional theory calculations and synthesized for efficient dye-sensitized solar cells (DSCs). Photophysical and electrochemical properties of these mediators derived from systematical functionalization of the framework with electron donating and withdrawing groups (MeO, Me, H, Cl, CF₃, and NO₂) are investigated. With this new class of organic mediators, the redox potential can be fine-tuned over a 170 mV range, overlapping the conventional I⁻/I₃⁻couple. Due to the suitable interplay of physical properties and electrochemical characteristics of the mediator involving electron-donating MeO group, the DSCs based on this mediator behave excellently in various kinetic processes such as dye regeneration, electron recombination, and mass transport. Thus, the MeO derivative of the mediator is identified as having the best performance of this series of redox shuttles. As inferred from electrochemical impedance spectroscopy and cyclic voltammetry measurements, the addition of graphene into the normal carbon counter electrode material dramatically improves the apparent catalytic activity of the counter electrode towards the MeO derivative of mediator, resulting in N719 based DSCs showing a promising conversion efficiency of 6.53% under 100 mW·cm⁻² simulated sunlight illumination.