Intermediate-phase engineering via dimethylammonium cation additive for stable perovskite solar cells.

Achieving the long-term stability of perovskite solar cells is arguably the most important challenge required to enable widespread commercialization. Understanding the perovskite crystallization process and its direct impact on device stability is critical to achieving this goal. The commonly employed dimethyl-formamide/dimethyl-sulfoxide solvent preparation method results in a poor crystal quality and microstructure of the polycrystalline perovskite films. In this work, we introduce a high-temperature dimethyl-sulfoxide-free processing method that utilizes dimethylammonium chloride as an additive to control the perovskite intermediate precursor phases. By controlling the crystallization sequence, we tune the grain size, texturing, orientation (corner-up versus face-up) and crystallinity of the formamidinium (FA)/caesium (FA)yCs1-yPb(IxBr1-x)3 perovskite system. A population of encapsulated devices showed improved operational stability, with a median T80 lifetime (the time over which the device power conversion efficiency decreases to 80% of its initial value) for the steady-state power conversion efficiency of 1,190 hours, and a champion device showed a T80 of 1,410 hours, under simulated sunlight at 65 °C in air, under open-circuit conditions. This work highlights the importance of material quality in achieving the long-term operational stability of perovskite optoelectronic devices.

Improving the photoresponse of copper(I) dyes in dye-sensitized solar cells by tuning ancillary and anchoring ligand modules.

The syntheses of five homoleptic copper(I) complexes [CuL2][PF6] are described in which L is a 4,4'-di(4-bromophenyl)-6,6'-dialkyl-2,2'-bipyridine ligand (compounds 1-4 with methyl, (n)butyl, (iso)butyl and hexyl substituents, respectively) or 4,4'-di(4-bromophenyl)-6,6'-diphenyl-2,2'-bipyridine (5). The new ligands 2-5 and copper(I) complexes [CuL2][PF6] (L = 1-5) have been fully characterized. The single crystal structures of 2{[Cu(1)2][PF6]}·3Me2CO, [Cu(2)2][PF6], 2{[Cu(3)2][PF6]}·Et2O and [Cu(5)2][PF6]·CH2Cl2 have been determined. The first three structures show similar distorted tetrahedral environments for the Cu(+) ions with angles between the least squares planes of the bpy domains of 85.6, 86.4 and 82.9°, respectively; in contrast, the Cu(+) ion in [Cu(5)2][PF6]·CH2Cl2 is in a flattened coordinate environment due to intra-cation face-to-face π-interactions. The solution absorption spectra of the complexes with ligands 1-4 are virtually identical with an MLCT band with values of λmax = 481-488 nm. In contrast, the absorption spectrum of [Cu(5)2][PF6] shows two broad bands in the visible region. Cyclic voltammetric data show that oxidation of the copper(I) centre occurs at a more positive potential in [Cu(2)2][PF6], [Cu(3)2][PF6] and [Cu(4)2][PF6] than in [Cu(1)2][PF6] or [Cu(5)2][PF6] with the latter being oxidized at the lowest potential. The complexes have been used to prepare dye-sensitized solar cells (DSCs) incorporating heteroleptic dyes of type [Cu(L)(Lanchor)](+) where L is 1-5 and Lanchor is a 6,6'-dimethyl-2,2'-bipyridine functionalized in the 4- and 4'-positions with phosphonic acid groups with (Lanchor = 7) and without (Lanchor = 6) a spacer between the metal-binding and anchoring domains. The presence of the spacer results in enhanced performances of the dyes, and the highest energy conversion efficiencies are observed for the dyes [Cu(3)(7)](+) (η = 2.43% compared to 5.96% for standard dye N719) and [Cu(5)(7)](+) (η = 2.89% compared to 5.96% for N719). Measurements taken periodically over the course of a week indicate that the cells undergo a ripening process (most clearly seen for [Cu(5)(6)](+) and [Cu(5)(7)](+)) before their optimum performances are achieved. IPCE (EQE) data are presented and confirm that, although the photo-to-current conversions are promising (37-49% for λmax≈ 480 nm), the copper(I) dyes do not realize the broad spectral response exhibited by N719.

Copper(I) dye-sensitized solar cells with [Co(bpy)3](2+/3+) electrolyte.

The hierarchical assembly of DSCs containing a new heteroleptic copper(I) complex with a phosphonic acid anchoring ligand is described; it is shown that conventional I(-)/I3(-) electrolytes may be replaced by [Co(bpy)3](2+/3+) with no loss in performance.

Hole-transport functionalized copper(I) dye sensitized solar cells.

Ligands containing first and second generation hole-transport triphenylamino-dendrons have been evaluated as ancillary ligands in copper(I) DSCs yielding an optimal efficiency of 3.77% in unmasked cells. The effects of masking the DSCs on measured parameters are discussed.