Improved hole mobility and suppressed trap density in polymer-polymer dual donor based highly efficient organic solar cells Available to Purchase

Here we report, the charge transport properties of polymer-polymer dual donor blended film, viz., polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) and poly [N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′benzothiadiazole) (PCDTBT) in the optimized concentration. Trap density and hole mobility in polymer-polymer (PTB7-PCDTBT) dual donor system have been studied by means of current density–voltage (J-V) characteristics at various temperatures, i.e., 280 K–120 K in hole only device configuration, i.e., indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulphonate) (PEDOT:PSS)/Polymer film/gold (Au). The J-V curves exhibit the space charge limited conduction behavior. The corresponding hole mobility for PTB7 and PCDTBT are 3.9 × 10⁻⁴ cm² V⁻¹ s⁻¹ and 2.1 × 10⁻⁴ cm² V⁻¹ s⁻¹, respectively, whereas it is 9.1 × 10⁻⁴ cm² V⁻¹ s⁻¹ in the polymer-polymer blend of PTB7:PCDTBT (0.7:0.3). This enhancement in mobility can be attributed to the suppressed trap density in PTB7:PCDTBT (0.7:0.3) of 7.4 × 10¹⁶cm⁻³, as compared to the trap density of 1.1 × 10¹⁷cm⁻³ for PTB7 and 1.6 × 10¹⁷cm⁻³ for PCDTBT. Atomic force microscopy shows an improvement in the morphology of the blend. The J–V characteristic at various light intensities in the bulk heterojunction (BHJ) solar cell reveals that the blending of PCDTBT in PTB7 suppressed the trap-assisted recombination. The corresponding power conversion efficiencies for PTB7:PC₇₁BM, PCDTBT:PC₇₁BM and PTB7:PCDTBT:PC₇₁BM BHJ solar cells are 6.9%, 6.1% and 9.0%, respectively. This work unravels that the enhanced mobility and suppressed trap density play a significant role in the improvement of efficiency in dual donor based organic solar cells.