Small molecule organic solar cells with enhanced near-IR photoactivity: The role of texturing and molecular architecture of the active layers on solar cell performance

Small molecule organic solar cells (OPV), using donor layers based on tetravalent and trivalent metal phthalocyanines (e.g. oxo-titanium TiOPc, or chloroindium ClInPc), are discussed here. As-deposited thin films of these Pcs undergo phase changes to form polymorphs with excellent near-IR photoactivity, accompanied by nano-texturing of the donor layers. In OPVs based on Pc/C₆₀ heterojunctions, this results in a factor of up to 5× increase in short-circuit photocurrents (J_SC) and power conversion efficiencies. Fully optimized single junction OPVs based on these materials may ultimately approach 6% efficiencies, however their biggest impact is in providing guidance for the formation of new, solution processable forms of these materials, which retain this near-IR sensitivity and high power conversion efficiencies.