Explanation of the photocurrent quantum efficiency (Φ) enhancements through the CAN's model equation for the p-Cul sensitized methylviolet-Cis LB films in the photoelectrochemical cells (PECs) and Cu/n-Cu_2O/M-C_(18)/p-CuI solid-state photovoltaic cells

摘要

Photocurrent enhancements in a dye sensitized photoelectrochemical cell (PEC) with a Cu/p-CuI/M-C_(18) photoelectrode and a dye sensitized solid state photovoltaic cell (DSSC) with Cu/n-Cu_2O/M-C_(18)/p-CuI are studied by controlling the formation of dye aggregates of M-C_(18) Langmuir-Blodgett (LB) films on the p-Cul layer. LB films of M-C_(18) are deposited under biasing conditions during the LB deposition process on Cu/p-CuI, Cu/n-Cu_2O/p-CuI and conductive glass plates with the three-electrode configuration setup coupling to the LB trough. LB films prepared under positive biasing conditions enhance the photocurrent quantum efficiencies for both PECs and DSSCs controlling and minimizing the formation of dye aggregates. The electrolyte used for LB deposition and photocurrent measurements is (10~(-2) M) Fe~(2+) + Fe~(3+) (10~(-2) M) and (10~(-2) M) NaH_2PO_4-Na_2HPO_4, pH = 6 buffer solution. Maximum photocurrent quantum efficiencies (Φmax%) obtained are≈22% for PEC and ≈20% for DSSCs, where the M-C_(18) LB film deposition applied potentials +0.3 V versus Ag/AgCl. The mechanism of the photocurrent enhancement is discussed through the CAN'S model equation, Φ = AD_0-BD_0~2, where A = k_1k_2/F, B = 1k_1~2 k_2[2k_6/F~3 + k_2k_4/k_3~2 X~2F~2], F = k_2 + k_5Y + k_7 + k1 I [1 + k_2/k_3 X], presented from our previous study [1]. Experimental evidence for the formation of the aggregates of M-C_18 LB films for the negative applied potentials and suppression of the aggregates with positive applied potentials are presented from absorption spectra, AFM pictures and fluorescence measurements of the samples. Conversion efficiency obtained is≈2.5%, V_(oc) ≈750 mV and I(sc) ≈ 5.8 mA cm~(-2) for DSSC fabricated with +0.3 V versus Ag/AgCl applied deposition potential of M-C_(18) LB films.