Bulk p-i-n heterojunction solar cells made from hyperbranched phthalocyanine polymers

A wet chemistry technique was developed to fabricate a new type of organic-inorganic hybrid solar cells with bulk p-i-n heterojunctions (“i”, an intrinsic absorber layer). Three new hyperbranched phthalocyanine polymers, namely H₂PPc, TiOPPc and CuPPc, have been synthesized and implanted into extremely-thin absorber (ETA) solar cells with a cell structure of indium tin oxide (ITO)/TiO₂ (n-type, made by sol gel method or Solaronix method)/TiO₂:phthalocyanine polymer/CuSCN/Au (or carbon) as the strong light-absorbing materials. The phthalocyanine polymers were prepared by cyclotetramerization reaction of 1,3-bis(3,4-dicyanophenoxy)benzene with/without respective metal salts under the catalysis of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The phthalocyanine polymers were mixed with TiO₂ sol gel and spin-coated onto n-type TiO₂ pre-coated ITO glass substrate, followed by casting a saturated CuSCN solution in dipropylsulfide to form a p-type semiconducting layer. After coating a counter electrode onto this p-type layer, a cell structure of ITO/TiO₂/TiO₂:phthalocyanine polymer/CuSCN/Au (or carbon) was thus fabricated. A power conversion efficiency of 0.23% has been achieved from these devices by our preliminary work. Successful application of organic semiconductors in ETA solar cells has been demonstrated.