Hybrid Phototransistors Based on Bulk Heterojunction Films of Poly(3-hexylthiophene) and Zinc Oxide Nanoparticle

Hybrid phototransistors (HPTRs) were fabricated on glass substrates using organic/inorganic hybrid bulk heterojunction films of p-type poly­(3-hexylthiophene) (P3HT) and n-type zinc oxide nanoparticles (ZnO_<i>NP</i>). The content of ZnO_<i>NP</i> was varied up to 50 wt % in order to understand the composition effect of ZnO_<i>NP</i> on the performance of HPTRs. The morphology and nanostructure of the P3HT:ZnO_<i>NP</i> films was examined by employing high resolution electron microscopes and synchrotron radiation grazing angle X-ray diffraction system. The incident light intensity (<i>P</i>_IN) was varied up to 43.6 μW/cm², whereas three major wavelengths (525 nm, 555 nm, 605 nm) corresponded to the optical absorption of P3HT were applied. Results showed that the present HPTRs showed typical p-type transistor performance even though the n-type ZnO_<i>NP</i> content increased up to 50 wt %. The highest transistor performance was obtained at 50 wt %, whereas the lowest performance was measured at 23 wt % because of the immature bulk heterojunction morphology. The drain current (<i>I</i>_D) was proportionally increased with <i>P</i>_IN due to the photocurrent generation in addition to the field-effect current. The highest apparent and corrected responsivities (<i>R</i>_A = 4.7 A/W and <i>R</i>_C = 2.07 A/W) were achieved for the HPTR with the P3HT:ZnO_<i>NP</i> film (50 wt % ZnO_<i>NP</i>) at <i>P</i>_IN = 0.27 μW/cm² (555 nm)

Light-Induced Open Circuit Voltage Increase in Polymer Solar Cells with Ternary Bulk Heterojunction Nanolayers

We report a light-induced open circuit voltage (<i>V</i>_OC) increase in polymer solar cells with ternary bulk heterojunction (BHJ) layers that are composed of poly­(3-hexylthiophene) (P3HT), poly­[(4,8-bis­(2-ethylhexyloxy)-benzo­[1,2-b:4,5-b′]­dithiophene)-2,6-diyl-<i>alt</i>-(N-2-ethylhexylthieno­[3,4-<i>c</i>]­pyrrole-4,6-dione)-2,6-diyl]] (PBDTTPD), and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM). The ternary BHJ layers were prepared by varying the composition of donor polymers at a fixed ratio (1:1 by weight) of donor (P3HT + PBDTTPD) to acceptor (PC₆₁BM). Results showed that <i>V</i>_OC was gradually increased under continuous illumination of solar light (100 mW/cm²) for ternary solar cells, whereas no <i>V</i>_OC increase was measured for binary solar cells without PBDTTPD. As a consequence, the power conversion efficiency (PCE) of ternary solar cells (except the highest PBDTTPD content) was rather higher after solar light illumination for 10 h, even though the binary solar cell exhibited significantly lowered PCE after 10 h illumination. The <i>V</i>_OC increase has been attributed to the lateral phase segregation between P3HT and PBDTTPD domains in the ternary BHJ layers under continuous illumination of solar light, as evidenced from the analysis result by Raman spectroscopy, atomic force microscopy, transmission electron microscopy, and synchrotron radiation grazing-incidence angle X-ray diffraction measurements