Brian L. Watson

Scaffold-reinforced perovskite compound solar cells

The relative insensitivity of the optoelectronic properties of organometal trihalide perovskites to crystallographic defects and impurities has enabled fabrication of highly-efficient perovskite solar cells by scalable solution-state deposition techniques well suited to low-cost manufacturing. Fracture analyses of state-of-the-art devices, however, have revealed that both the perovskite active layer and adjacent carrier selective contacts are mechanically fragile—a major obstacle to technological maturity that stands to significantly compromise their thermomechanical reliability and operational lifetimes. We report a new concept in solar cell design, the compound solar cell (CSC), which addresses the intrinsic fragility of these materials with mechanically reinforcing internal scaffolds. The internal scaffold effectively partitions a conventional monolithic planar solar cell into an array of dimensionally scalable and mechanically shielded individual perovskite cells that are laterally encapsulated by the surrounding scaffold and connected in parallel via the front and back electrodes. The CSCs exhibited a significantly increased fracture energy of ∼13 J m−2—a 30-fold increase over previously reported planar perovskite (∼0.4 J m−2)—while maintaining efficiencies comparable to planar devices. Notably, the efficiency of the microcells formed within the scaffold is comparable to planar devices on an area-adjusted basis. This development is a significant step in demonstrating robust perovskite solar cells to achieve increased reliability and service lifetimes comparable to c-Si, CIGS, and CdTe solar cells.

Synthesis and use of a hyper-connecting cross-linking agent in the hole-transporting layer of perovskite solar cells

Solution-processed organic semiconducting materials feature prominently in modern optoelectronic devices, especially where low-cost and flexibility are specific goals, such as perovskite solar cells. Their intrinsic solubility, poor cohesion and lack of adhesion to underlying substrates, however, curtail their scope of application and durability. To overcome this, a mechanically stiff, light-activated, tetra-azide cross-linking agent, 1,3,5,7-tetrakis-(p-benzylazide)-adamantane (TPBA), has been developed to transform solution processed organic polymers into solvent-resistant and mechanically tough films. The use of 3-azidopropyltrimethoxysilane (AzPTMS) has been developed as a light-activated adhesion promotor, enabling mechanical testing of toughened, cross-linked polymers. Lithium bis(trifluoromethane)sulfonimide (LiTFSI) doped poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine, poly(triaryl amine) (PTAA), a hole-transporting material used in perovskite solar cells, has been selected as a candidate system for demonstrating the utility of TPBA to transform a fragile and highly-soluble hole-transporting organic semiconductor into a mechanically tough and solvent-resistant semiconducting composite. TPBA enables the solvent resistance and mechanical toughness of PTAA to be tuned without compromising the electronic functionality of the semiconducting material. While increasing the fracture toughness of PTAA by over 300%, TPBA cross-linking also enables fabrication of perovskite solar cells with increased photovoltaic efficiencies in n–i–p and p–i–n geometries, and promotes adhesion of the doped polymer to the perovskite layer, mitigating interfacial device failure.

Mechanical integrity of solution-processed perovskite solar cells

The fracture of a variety of solution-processed organometal trihalide perovskite solar cells and isolated perovskite layers is reported. The study covers cells in which the perovskites, including planar and mesoporous layers, are deposited by an array of solution-state deposition techniques and feature a wide variety of ancillary organic and inorganic charge transport layers. Understanding the influence of materials selection and fabrication techniques on mechanical stability is an important step towards realizing mechanically robust perovskite cells.

Cross-linkable styrene-functionalized fullerenes as electron-selective contacts for robust and efficient perovskite solar cells

Styrene functionalized fullerene derivatives have been designed for use as electron-selective contacts in perovskite solar cells. Unlike films of PC61BM and C60 fullerene, films of these styrene-functionalized fullerenes (SFFs) can be transformed into a solvent resistant material through thermal curing. Conventional-geometry perovskite solar cells utilizing cured and uncured thin films of SFFs on titania were fabricated and tested for PCE and fracture resistance, and compared to cells employing C60. These cells displayed significant improvements in the fracture resistance (> 200 %) while exhibiting only a 7% drop in PCE (13.8 % vs 14.8 % PCE), with larger VOC and JSC values in comparison to the C60 control cell. Inverted cells fabricated with SFFs displayed an even greater increase in fracture resistance (> 400 %) with only a 6 % reduction in PCE (12.3 % vs 13.1 %) in comparison to those utilizing PC61BM.

Low-cost, single-step hybrid bond/barrier films for Cu bondlines in advanced packaging

The presence of weak Cu-oxides has detrimental implications for the adhesion, moisture sensitivity, stress-and electro-migration of Cu bondlines in advanced packaging, often leading to premature device failure. We report on a novel, low-cost, single-step sol-gel synthetic route capable of reducing the weak Cu-oxide while simultaneously depositing a high-performance hybrid film, which acts both as an adhesion layer at the Cu/epoxy interface, as well as potentially a barrier film that prevents moisture degradation and Cu stress- and electro-migration.