Extraction current transients for mobility determination—A comparative study

Abstract

In this work, we measure the hole mobility in the model polymer system poly(3-hexylthiophene-2,5-diyl) by using different measurement techniques. Our main purpose is to determine how the recently developed charge extraction by a linearly increasing voltage technique for metal–insulator–metal devices (MIM-CELIV) compares to other commonly used methods, such as space charge limited currents and time-of-flight. Our findings suggest that the MIM-CELIV technique gives a slightly lower mobility than the other techniques, which is understandable given that the method measures the mobility of relaxed charge carriers in the dark unlike, for example, time-of-flight where charge carriers are photogenerated. In addition, we scrutinize the accuracy and reliability of the techniques used, showing that differences in mobility smaller than a factor of two are not detectable unless statistics from many devices are available.

Analytical description of mixed ohmic and space-charge-limited conduction in single-carrier devices

“…1a), and are amongst the most commonly used methods for determining charge-carrier mobilities, μ, of relatively intrinsic semiconductors. [1][2][3][4][5][6][7] SCLC measurements are highly popular due to the fact that: i) The single-carrier devices used for SCLC measurements are relatively easy to fabricate and operate under similar conditions to that of optoelectronic devices; ii) fabricating single-carrier devices does not require a large amount of material, which is beneficial when newly-developed semiconductors are being probed where material is scarce; iii) SCLC measurements are relatively easy to perform and do not require access to powerful magnets or lasers; iv) charge transport of electrons and holes can be probed separately by an appropriate choice of contacts, and; v) SCLC measurements can yield information about energetic disorder, doping and traps if proper models are used to interpret the results. SCLC measurements have therefore become a standard method to characterize a wide variety of novel semiconductors, such as metal chalcogenides, 8 amorphous silicon, 9 organic semiconductors, [10][11][12] fullerenes, 13,14 and metal-halide perovskites.…”

Requirements for Making Thick Junctions of Organic Solar Cells based on Nonfullerene Acceptors

“…Charge carrier mobilities were determined using Resistance‐dependent photovoltage (RPV), [ 29 ] metal–insulator–metal charge extraction by a linearly increasing voltage (MIM‐CELIV) [ 30,31 ] and metal–insulator–semiconductor charge extraction by a linearly increasing voltage (MIS‐CELIV). [ 32,33 ] RPV and MIM‐CELIV were carried out on PM6:Y6 solar cells with inverted device structures (glass/ITO/ZnO/active layer/MoO 3 /Ag).…”

“…We note that a mobility imbalance of a factor of three seen in the MIS‐CELIV measurements are probably not resolvable in RPV explaining why only one transit time is observed in RPV (Figure S1, Supporting Information). In addition, the error in the mobility determination is typically up to a factor of two with these techniques [ 31 ] ; it is therefore possible that the mobility imbalance is significantly larger, or indeed smaller.…”

How to Reduce Charge Recombination in Organic Solar Cells: There are Still Lessons to Learn from P3HT:PCBM

“…As RPV is carried out under much lower carrier densities, the latter might point to a slight carrier density dependence of μ p , but is within the typical range when comparing different mobility measurements methods. [69] However, the important fact is that there is still no significant difference between the CB and DCB blends. This shows that also the (macroscopic) transport of photogenerated charges is only slightly influenced by the differences in morphology.…”