Influence of Charge Transport and Defects on the Performance of Planar and Mesostructured Perovskite Solar Cells

Abstract

describing charge transport are the carrier mobility, charge generation/extraction, and carrier lifetime observed in fully assembled, operating solar cells. [5] There are several well-known experimental approaches toward estimation of these parameters including time-of-flight (TOF) photoconductivity, [6] space charge limited current (SCLC), [7] field-effect transistor (FET), [8] and charge extraction by linearly increasing voltage (CELIV). [9,10] However, each of them is hindered by an array of limitations. In principle, most commonly utilized TOF photoconductivity measurement is operated in direct current mode and requires application of very thick film in order to provide surface photogeneration for reliable observation of charge transport features, as well as the transit time. In addition, light bias is kept very low, ensuring charge carrier concentration to be much lower than the charge stored on the electrodes, resulting in constant electric field across the measured sample. These prerequisites are difficult to meet in the case of efficient thin film perovskite-based solar cells, especially when planar architecture is taken into consideration, as these devices are generally sub 500 nm thick. On the other hand, SCLC technique also comes with a set of drawbacks reflected through relationship between injected charge and distribution of occupancy within localized states, leading to oversimplification of results in respect to trapping states, sample homogeneity, temperature dependence, as well as quality of contact between electrodes and semiconductor. [11] In the case of charge mobility, poor injection of faster carriers in cells with unbalanced transport often leads to overestimation of retrieved values. Alternatively, dark injection SCLC can be utilized to study very thin films in a fashion highly similar to TOF, with exception of voltage step being used for generation of charge carriers instead of a laser pulse. The charge mobility obtained from FET measurement depends on the type of electrodes, semiconductor-dielectric interface, and the charge carrier concentration. Moreover, device geometry used for FET measurements differs considerably from diode configuration, thus charge transport properties obtained from FET architecture may not reliably reflect charge transport behavior of diode structures. CELIV has been widely used as a reliable tool in characterization of organic solar cells, [12,13] relying on triangle voltage Photoinduced charge selective carrier extraction by linearly increasing voltage technique allows straightforward assessment of charge transport properties within planar and mesostructured perovskite solar cells with respect to light intensity and signal delay time. Charge sensitive device architecture is realized through implementation of insulating layer between the anode or cathode to prevent extraction of unwanted type of carriers. Resulting behavior of comparatively efficient mesoporous and planar solar cells exhibits well balanced charge transport with slight dependence of charge mobili...

Limitations of a polymer-based hole transporting layer for application in planar inverted perovskite solar cells

“…56,57 Moreover, we note the absence of any apparent charge reservoir, as this occurrence would enhance the random-walk mechanism during the carrier transport and cause a decay trend of higher orders. 58,59 As mentioned earlier, all transient decays in our case exhibited a mono-exponential trend which is not indicative of any effectual accumulation of charge carriers. 60 The full set of TPV transients taken at each step of UV degradation is given in the ESI (Fig.…”

Insights into charge carrier dynamics in organo-metal halide perovskites: from neat films to solar cells

“…Similarly, by modified photo-CELIV, nondispersive electron transport was also observed in planar MAPbI 3 solar cells caused by the passivating function of PCBM, while dispersive electron transport was clearly observed in mesoporous perovskite devices due to the presence of traps at the TiO 2 / MAPbI 3 interface. 27 This work further emphasized the importance of the PCBM layer in achieving a nondispersive nature in perovskite devices.…”

“…More recently, a modified photo-CELIV method was taken to separately measure the hole and electron mobilities of perovskites by inserting a 100 nm-thick MoO 3 layer in front of the selected electrodes to block the unwanted type of carrier. 27 To uncover the effect of the device structure on transport dynamics, mesoporous and inverted planar MAPbI 3 devices were comparatively investigated as shown in Fig. 3C.…”

High performance perovskite sub-module with sputtered SnO2 electron transport layer

“…However, the instability of perovskite absorber materials (Correa-Baena et al, 2017) and difficulty in large area fabrication devices (Li et al, 2018b) is still serious problems for future commercialization of p e r o v s k i t e -b a s e d s o l a r c e l l . So far, the planar n-i-p structured PSCs (Halvani Anaraki et al, 2018;Yang et al, 2018a) shows great promise due to their easier upscaling deposition of electron transport layers (ETLs) compared to mesostructured PSCs (Petrović et al, 2017). And there are lots of fabrication methods (Chen et al, 2019) have been reported to efficiently deposit thin ETL films, however, not all the methods are suitable for achieving uniform large area high quality thin films for large area perovskite solar modules (PSMs).…”