Increasing the stability of perovskite solar cells is a major challenge for commercialization. The highest efficiencies so far have been achieved in perovskite solar cells employing mesoporous TiO 2 (m-TiO 2 ).One of the major causes of performance loss in these m-TiO 2 -based perovskite solar cells is induced by UV-radiation. This UV instability can be solved by replacing TiO 2 with SnO 2 ; thus developing a mesoporous SnO 2 (m-SnO 2 ) perovskite solar cell is a promising approach to maximise efficiency and stability. However, the performance of mesoporous SnO 2 (m-SnO 2 ) perovskite solar cells has so far not been able to rival the performance of TiO 2 based perovskite solar cells. In this study, for the first time, high-efficiency m-SnO 2 perovskite solar cells are fabricated, by doping SnO 2 with gallium, yielding devices that can compete with TiO 2 based devices in terms of performance. We found that gallium doping severely decreases the trap state density in SnO 2 , leading to a lower recombination rate. This, in turn, leads to an increased open circuit potential and fill factor, yielding a stabilised power conversion efficiency of 16.4%. The importance of high-efficiency m-SnO 2 based perovskite solar cells is underlined by stability data, showing a marked increase in stability under full solar spectrum illumination.

Inspired by momentum in applications of reductive photoredox catalysis to organic synthesis, photodriven transfer hydrogenations toward deep (>2 e − ) reductions of small molecules are attractive compared to using harsh chemical reagents. Noteworthy in this context is the nitrogen reduction reaction (N 2 RR), where a synthetic photocatalyst system had yet to be developed. Noting that a reduced Hantzsch ester (HEH 2 ) and related organic structures can behave as 2 e − /2 H + photoreductants, we show here that, when partnered with a suitable catalyst (Mo) under blue light irradiation, HEH 2 facilitates delivery of successive H 2 equivalents for the 6 e − /6 H + catalytic reduction of N 2 to NH 3 ; this catalysis is enhanced by addition of a photoredox catalyst (Ir). Reductions of additional substrates (nitrate and acetylene) are also described.

Whereas photoredox catalysis using molecular systems enjoys considerable utility in small molecule transformations and reactions relevant to organic synthesis, to date there are no related examples of photodriven catalytic nitrogen fixation. We wondered whether a photoinduced transfer hydrogenation strategy might provide a viable pathway toward such a reaction. Hantzsch esters (and related organic structures) offer an opportunity for catalysis design in this context as they can behave as photoreductants, though to our knowledge they had yet to be shown to be compatible with such a redox intensive process (6 e–/6 H+). In the present study we demonstrate that fully reduced Hantzsch esters (abbreviated as HEH2) successively deliver stored H2-equivalents to N2, producing NH3 catalytically, in the presence of a molecular precatalyst (Mo) under blue-light irradiation but otherwise ambient conditions. While not required for the observed photocatalysis, the addition of a photoredox catalyst (Ir) to the reaction mixture enhances both the rate and turnover number of the net transformation. Encouraging with respect to future studies toward recycling the donor, electrochemically or via hydrogenation, other N-heterocycle H2-donors are also compatible with catalysis in the presence of the photoredox catalyst. The reduction of N2 to NH3 by HEH2 or H2 are thermodynamically very similar (ΔΔGf(NH3) = 1.8 kcal mol–1 in acetonitrile). However, whereas the combination of H2 with N2 to produce NH3 is accomplished via high temperature and pressure over a metal catalyst, the needed overpotential to drive the reduction of N2 by HEH2 can instead be derived from light. This study hence illustrates a promising photoredox catalysis approach toward deep reduction of robust small molecule substrates via photoinduced transfer hydrogenation, with the complete reduction of the triple bond of N2 providing a vivid example.