text: Although there is significant insight as to how OPVs work, it is still difficult to relate the devices functionality to local film structures. This difficulty may be attributed to the minimal current generation at a given point within OPVs. Through pc-AFM, OPV devices can be probed at nano-scale level and can help to increase our fundamental knowledge of mechanisms involved in OPVs at nano-scale level. pc-AFM is capable of gathering information such as the mapping of photocurrents, differences in film morphology, determination of donor-acceptor domains, current density-voltage plots, quantum efficiencies, and approximate charge carrier mobilities. One of the other notable characteristics of pc-AFM is its ability to provide concurrent information regarding the topological and photocurrent properties of the device at nano-scale. Using this concurrent sampling method, the sample handling is minimized and can provide more accurate results. In a study by Pingree et al., pc-AFM was used to measure how spatial deviations in the photocurrent generation developed with different processing techniques. The authors were able to compare these photocurrent variations to the duration of the annealing process. They have concluded that lengthening the annealing time allows for improved nano-scale phase separation as well as created a more ordered device. Actual times for the annealing process vary depending on the properties of the polymers used. The authors have shown that external quantum efficiency (EQE) and power conversion efficiency (PCE) levels reach a maximum at certain annealing times whereas while the electron and hole mobilitys do not show the corresponding trends. Therefore, while lengthening the annealing time can increase the photocurrents within the OPV, there is a practical limit to after which the benefits may not be substantial. Besides functional properties, pc-AFM can also be used to interrogate the composition heterogeneity of OPVs when combined with either Raman or infrared (IR) spectroscopy, and it is especially valuable for studying their degradation.
  In more recent studies, pc-AFM has been employed to gather information regarding the photoactive regions from the use of quantum dots. Because if their relative ease of use, along with size-tunable excitation attributes, quantum dots have commonly been applied as sensitizers in optoelectronic devices. The authors have studied the photoresponse of sub-surface foundations such as buried indium arsenide (InAs) quantum dots through the implementation of pc-AFM. Through the use of pc-AFM, information regarding quantum dot size, as well as the dispersion of quantum dots within the device, can be recorded in a non-destructive manner. This information can then be used to display local variances in photoactivity relating to heterogeneities within the film morphology.