Charge-carrier photogeneration and extraction dynamics of polymer solar cells probed by a transient photocurrent nearby the regime of the space charge-limited current

To understand the complex behaviors of photogenerated charge carriers within polymer-based bulk-heterojunction-type solar cells,the charge-carrier photogeneration and extraction dynamics are simultaneously estimated using a transient photocurrent technique under various external-bias voltages,and a wide range of excitation intensities are analyzed.For this purpose,conventional devices with 80 nm thick active layers consisting of a blend of representative P3HT and PTB7 electron-donating polymers and proper electron-accepting fullerene derivatives were used.After the correction for the saturation behavior at a high excitation-intensity range nearby the regime of the space charge-limited current,the incident-photon-density-dependent maximum photocurrent densities at the initial peaks are discussed as the proportional measures of the charge-carrier-photogeneration facility.By comparing the total number of the extracted charge carriers to the total number of the incident photons and the number of the initially photogenerated charge carriers,the external quantum efficiencies as well as the extraction quantum efficiencies of the charge-carrier collection during a laser-pulse-induced transient photocurrent process were obtained.Subsequently,the charge-carrier concentration-dependent mobility values were obtained,and they are discussed in consideration of the additional influences of the charge-carrier losses from the device during the charge-carrier extraction that also affects the photocurrent-trace shape.

Long-lasting photoluminescence quantum yield of cesium lead halide perovskite-type quantum dots

Cesium lead halide perovskite(CsPbX_(3),X=Cl,Br,I)quantum dots(QDs)and their partly Mn^(2+)-substituted QDs(CsPb1–xMnxX3)attract considerable attention owing to their unique photoluminescence(PL)efficiencies.The two types of QDs,having different PL decay dynamics,needed to be further investigated in a form of aggregates to understand their solid-state-induced exciton dynamics in conjunction with their behaviors upon degradation to achieve practical applications of those promising QDs.However,thus far,these QDs have not been sufficiently investigated to obtain deep insights related to the long-term stability of their PL properties as aggregated solid-states.Therefore,in this study,we comparatively examined CsPbX_(3)-and CsPb1–xMnxX_(3)-type QDs stocked for>50 d under dark ambient conditions by using excitation wavelength-dependent PL quantum yield and time-resolved PL spectroscopy.These investigations were performed with powder samples in addition to solutions to determine the influence of the inter-QD interaction of the aged QD aggregates on their radiative decays.It turns out that the Mn^(2+)-substituted QDs exhibited long-lasting PL quantum efficiencies,while the unsubstituted CsPbX_(3)-type QDs exhibited a drastic reduction of their PL efficiencies.And the obtained PL traces were clearly sensitive to the sample status.This is discussed with the possible interaction depending on the size and distance of the QD aggregates.