Voltage Dependence Of Photocurrent Research Articles

Buried junction and efficient carrier separation in CdSexTe1−x/CdTe solar cells

Alloying CdTe absorbers with Se is a critical advancement for the fabrication of highly efficient CdTe thin-film solar cells. Herein, the role of the Se concentration gradient in CdSexTe1−x/CdTe solar cells is stressed in addition to the decreased bandgap and passivation effect of Se. The buried graded CdSexTe1−x at the front interface of the device was stripped and analyzed by quasi in situ x-ray photoelectron spectroscopy depth profiling. A serial shift of Fermi level toward the valence band was probed as the Se concentration decreased in the graded CdSexTe1−x absorber, revealing the presence of n-type CdSexTe1−x region near the front contact. Kelvin probe force microscopy characterizations and voltage-dependent photocurrent collection analysis further confirmed the existence of a buried junction in the graded CdSexTe1−x absorber. The CdS-free CdTe solar cell with a graded CdSexTe1−x/CdTe absorber fabricated in this study showed an efficiency of 17.6%. These results indicated that the non-uniform distribution of Se introduced a built-in field in the graded CdSexTe1−x absorber and enabled efficient separation of photogenerated carriers, yielding high-performance CdTe solar cells in the absence of a conventional n-type CdS window layer. This study deepened the understanding of the performance enhancement in Se-containing CdTe solar cells and provided new ideas for further performance optimization.

Unraveling the Mechanism of the 150-Fold Photocurrent Enhancement in Plasma-Treated 2D TMDs.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are increasingly investigated for applications such as optoelectronic memories, artificial neurons, sensors, and others that require storing photogenerated signals for an extended period. In this work, we report an environment- and gate voltage-dependent photocurrent modulation method of TMD monolayer-based devices (WS2 and MoS2). To achieve this, we introduce structural defects using mild argon–oxygen plasma treatment. The treatment leads to an extraordinary over 150-fold enhancement of the photocurrent in vacuum along with an increase in the relaxation time. A significant environmental and electrostatic dependence of the photocurrent signal is observed. We claim that the effect is a combined result of atomic vacancy introduction and oxide formation, strengthened by optimal wavelength choice for the modified surface. We believe that this work contributes to paving the way for tunable 2D TMD optoelectronic applications.

Recombination-induced voltage-dependent photocurrent collection loss in CdTe thin film solar cell

Recently, the efficiency of CdTe thin film solar cell has been improved by using new type of window layer Mg x Zn1−x O (MZO). However, it is hard to achieve such a high efficiency as expected. In this report a comparative study is carried out between the MZO/CdTe and CdS/CdTe solar cells to investigate the factors affecting the device performance of MZO/CdTe solar cells. The efficiency loss quantified by voltage-dependent photocurrent collection efficiency (η C(V′)) is 3.89% for MZO/CdTe and 1.53% for CdS/CdTe solar cells. The higher efficiency loss for the MZO/CdTe solar cell is induced by more severe carrier recombination at the MZO/CdTe p–n junction interface and in CdTe bulk region than that for the CdS/CdTe solar cell. Activation energy (E a) of the reverse saturation current of the MZO/CdTe and CdS/CdTe solar cells are found to be 1.08 eV and 1.36 eV, respectively. These values indicate that for the CdS/CdTe solar cell the carrier recombination is dominated by bulk Shockley–Read–Hall (SRH) recombination and for the MZO/CdTe solar cell the carrier recombination is dominated by the p–n junction interface recombination. It is found that the tunneling-enhanced interface recombination is also involved in carrier recombination in the MZO/CdTe solar cell. This work demonstrates the poor device performance of the MZO/CdTe solar cell is induced by more severe interface and bulk recombination than that of the CdS/CdTe solar cell.

Effect of Annealing Temperature on Structural, Photoluminescence and Photoconductivity Properties of ZnO Thin Film Deposited on Glass Substrate by Sol–Gel Spin Coating Method

In this work, zinc oxide (ZnO) thin films have been deposited on glass substrate using a simple and inexpensive multi-step sol–gel spin coating method at annealing temperatures of 300, 400, 500 and 600 °C in an open atmosphere. The influence of annealing on structural, photoluminescence and photoconductivity properties of ZnO thin films has been systematically investigated. X-ray diffraction pattern reveals that all ZnO thin films are polycrystalline with hexagonal wurtzite structure. Scanning electron micrograph depicted the formation of ZnO nanofibrous structure. Photoluminescence properties of ZnO thin films have been investigated by photoluminescence spectroscopy at room temperature. Photoconductivity properties have been investigated in terms of several parameters such as voltage dependence of photocurrent and dark current as well as time-resolved rise and decay of photocurrent. The rise and decay spectra under periodic illumination show reproducible and stable photoresponse. The synthesized ZnO thin film seems to be having potential use in UV–Vis photodetectors.

Studying of photo-excitation dynamics and photodetector based on MoSe2 nanosheet

The photo-excitation dynamics occurring in the nanosheet of MoSe2 have been studied by employing the transient absorption. We find that four types of dynamic behaviors participate in the relaxation of excited MoSe2 nanosheet by global fitting, which corresponds to the exciton-exciton interaction, exciton capture by trapping state, exciton dissociation and free charge movement. Since many free charge has generated after photo-excitation, the photo-detector based on MoSe2 nanosheet is fabricated and the period- and voltage-dependent photocurrent is further clarified. In addition, nanosecond transient photocurrent test probes the dynamics of carrier and confirms that illumination intensity would accelerate the lifetime of carrier recombination to 1 μs at high intensity and enhance the corresponding loss of carrier. Moreover, it is also found that the bias voltage would linearly facilitate the yield of free carriers in photo-detector and the lifetime of carrier recombination would decrease to 4 μs at 60 V. The final results could help people to further understand the photo-physical property of MoSe2 nanosheet and facilitate its application in the opto-electronic devices.

Synthesis and characterization of magnesium doped ZnO nanostructures: methane (CH4) detection

Synthesis of magnesium doped zinc oxide nanostructures has been carried out by vapor transport method and characterization of the samples have been performed regarding methane (CH4) gas sensing in addition to their structural, morphological, chemical composition and optical properties. The un-doped and magnesium doped zinc oxide nanostructures were synthesized on silicon substrates at 900 °C through vapor liquid solid mechanism. Powder X-ray diffraction study confirmed the growth of material exhibiting crystalline wurtzite (hexagonal) structure. Scanning electron microscopy revealed that morphology of grown material is in the form of nanorods and nanobelts with average diameter and thickness of 12.66 ± 3.72 µm and 1.88 ± 0.70 µm, respectively. Energy dispersive X-ray analysis was used to examine the stoichiometry of the samples. Optical characterizations were carried out by photoluminescence, diffused reflectance spectroscopy, voltage dependent photo-current response and Time dependent photocurrent response. A significant change in energy bandgap has been observed after Mg incorporation in ZnO. For doped ZnO samples, the observed value of band gap is 3.32 eV which is higher than that for undoped ZnO (3.18 eV).The nanostructures were tested for UV and gas sensing properties based on the change in resistance in UV light when exposed to CH4 gas. The gas sensing response was recorded for temperature ranging from 50 to 200 °C for 400 ppm concentration of methane gas. The sensing response of Mg-doped ZnO nanobelts was found as high as 54%. The Mg-doped ZnO nanobelts showed significant, stable and enhanced sensing properties (54%) towards 400 ppm of CH4 gas at optimal temperature of 200 °C. The observations revealed that Mg doping in ZnO nanostructures would help to improve the CH4 and UV sensing of these materials.

Analytical modelling for p-i-n structured semiconductor devices

An analytical model for illuminated p-i-n structures such as Solar Cells and related devices has been developed. Starting from the semiconductor equations in their most general form, and introducing assumptions for the recombination and electrical field functions, it is aimed at modelling not only the collection of photogenerated carriers but all transport mechanisms such as carrier drift and diffusion. Using this model, the behaviour of thin film cells which is observed in operation is described in detail. This includes the dependencies of I/V curves on temperature, insolation and spectral effects, and electronic materials properties. The modeling of recombination effects results in a voltage dependent photocurrent where the carrier collection efficiency depends on the bias voltage. This model allows for relatively fast calculation of I/V curves as it is computationally less extensive than full device numerical simulations. Therefore it may be applicable for compact models i.e. in solar cell performance modelling.

In-depth investigation of the charge extraction efficiency for thermally annealed inverted bulk-heterojunction solar cells

The performance of bulk-heterojunction solar cells is significantly affected by several factors among which are the nano-morphology of the photoactive layer and the properties of interfacial layers promoting charge extraction and collection at the electrodes. In this work, we investigate the correlation between the MoOx layer thickness and the thermal annealing procedure on the device performance and on the charge extraction efficiency of inverted ITO/PEI/P3HT:PCBM/MoOx/Ag bulk heterojunction solar cells. The surface morphology of pristine and annealed P3HT:PCBM photoactive layers is examined by atomic force microscopy before and after the exposure to dichloromethane revealing that the distribution of the amorphous regions within the P3HT:PCBM layers can be related to the applied thermal annealing procedure. The chemical and molecular composition profiles in the photoactive layer and at the interfaces are investigated through depth profile analyses combining X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry showing a decreasing oxidation gradient of the MoOx and low diffusion of the MoOx species in the P3HT:PCBM layer. Additionally, we show that the voltage dependent photocurrent is significantly affected by non-geminate recombination for devices with a too thin MoOx layer thickness, while applying a non-optimal thermal annealing procedure leads to increased geminate recombination of charge carriers. The highest charge extraction efficiency and device performance is reached for devices with a MoOx layer above 5 nm while thermal annealing procedure has to be applied before the deposition of the MoOx/Ag layers.

A path-finding toward high-efficiency penternary Cu(In,Ga)(Se,S)2 thin film solar module

The optimal p-n junction structure in a state-of-the-art Cu(In,Ga)(Se,S)2 thin-film solar module technology is investigated. For co-optimization design and path-finding, a TCAD model is developed with experimental samples. The engineerable parameters, i.e., FGa, GGIavg, and CdS thickness, are demonstrated to play a critical role in determining the p-n junction properties such as dark current characteristics Jdark(V), voltage-dependent photocurrent, localized carrier collection efficiency, and interface carrier transportation. We show the optimal Ga-grading is determined by a trade-off between the recombination loss in space charge region and the photo-carrier collection in quasi-neutral region. The optimal CdS thickness is determined by a trade-off between carrier collection efficiency, short-circuit current (JSC) loss, and Jdark(V), which depends on varied Ga-profiles. Overall, thin CdS (≦10 nm) is preferred to reduce the JSC loss in accumulated Ga-profiles, while thicker CdS is preferred to enhance the carrier collection efficiency in flatter Ga-profiles. The band alignment effect on varied Cu(In,Ga)(Se,S)2/CdS junctions is also investigated. It is found sulfur-incorporation can suppress the VOC saturation behavior at wide bandgap. For CIGSeS absorber with SS = 20% and DP =15%, the maximum VOC of 780 mV can be achieved by co-optimized Ga-profile. Furthermore, varied Ga-profiles and CdS buffer layers are explored for pathfinding. An optimal p-n junction structure shows a relative +40% efficiency improvement from 15.5% to 21.9%. This work shows the efficiency headroom of reported CIGSeS thin-film solar module technology through co-optimized CIGSeS composition gradient and buffer layer.

Functional characterization of sodium-pumping rhodopsins with different pumping properties.

Sodium pumping rhodopsins (NaRs) are a unique member of the microbial-type I rhodopsin family which actively transport Na+ and H+ depending on ionic condition. In this study, we surveyed 12 different NaRs from various sources of eubacteria for their electrophysiological as well as spectroscopic properties. In mammalian cells several of these NaRs exhibited a Na+ based pump photocurrent and four interesting candidates were chosen for further characterization. Voltage dependent photocurrent amplitudes revealed a membrane potential-sensitive turnover rate, indicating the presence of an electrically-charged intermediate(s) in the photocycle reaction. The NaR from Salinarimonas rosea DSM21201 exhibited a red-shifted absorption spectrum, and slower kinetics compared to the first described sodium pump, KR2. Although the ratio of Na+ to H+ ion transport varied among the NaRs we tested, the NaRs from Flagellimonas sp_DIK and Nonlabens sp_YIK_SED-11 showed significantly higher Na+ selectivity when compared to KR2.All four further investigated NaRs showed a functional expression in dissociated hippocampal neuron culture and hyperpolarizing activity upon light-stimulation. Additionally, all four NaRs allowed optical inhibition of electrically-evoked neuronal spiking. Although efficiency of silencing was 3–5 times lower than silencing with the enhanced version of the proton pump AR3 from Halorubrum sodomense, our data outlines a new approach for hyperpolarization of excitable cells without affecting the intracellular and extracellular proton environment.

Photoconductivity and Luminescence Properties of Gadolinium Doped Zinc Oxide

In the present work, an attempt has been made to study photoconductivity and dark conductivity in gadolinium doped zinc oxide in air as well as in vacuum synthesized by heat treatment method. Structural and morphological studies have been performed using XRD and SEM respectively. XRD indicates that ZnO:Gd (5.0%) is having mixed phase of ZnO and Gd2O3. SEM images of ZnO:Gd (5.0%) indicates formation of spherical shaped particles of size lying in the range of 200–400 nm. UV–visible absorption spectra in undoped ZnO and Gd doped ZnO show absorption edges at 385 and 380 nm respectively. Photoluminescence (PL) spectrum of undoped ZnO exhibits peaks centered around at 401, 418, 455, 481 and 522 nm. Gd doped ZnO exhibits almost similar peaks. The PL spectra revealed various Zn and O related native defects (eg. vacancies, interstitials, antisites etc.) Voltage dependence of photocurrent and dark current is measured at room temperature under UV–visible illumination. Rise and decay curves exhibit anomalous behavior of photocurrent in air as well as in vacuum where in the photocurrent decreases even during steady illumination.

Organic photodiodes from homochiral l-proline derived squaraine compounds with strong circular dichroism.

We suggest and explore a novel route towards organic photodetectors sensitive to the circular polarization state of light. For this, we insert fullerene-blended thin films of homochiral squaraine compounds acting as a highly circular dichroic active layer into conventional bulk hetero-junction photodiodes. Initially, we discuss steady-state characterization of photodiodes with unpolarized light. The homochiral, l-proline derived squaraine compounds are obtained via a chiral pool synthesis in sizable quantities. The aggregation behavior of the two compounds with varying side chain length is complex. They exhibit H-type spectral signatures only in colloidal solution, and both H- and J-type features with large splitting in neat and fullerene-blended thin films. We probe strong excitonic circular dichroism for both aggregate species, showing the most competitive dissymmetry factors up to -0.055 in fullerene-blended thin films. We vary the blend ratio and layer thickness of such active layers in the photodiodes. The device performance is in all cases limited by a low fill factor which is accompanied by a voltage-dependent photocurrent. Current-voltage measurements show light intensity dependent characteristics, which are S-shaped, contrary to our expectations, only for thin active layers independent of the blend ratio. The external quantum efficiency is in some cases extraordinarily high, exceeding 100 percent in the blue spectral range under modest reverse bias voltages for thin, fullerene-rich devices. However, the most promising are the devices with thick, donor-rich layers defined by a spectral overlap of the strongest photocurrent response and the maximum circular dichroism within the green spectral range. Thus, we demonstrate the feasibility of combining photodiode functionality and strong circular dichroism as intrinsic material properties.

Comparison of CIGS Solar Cells Made With Different Structures and Fabrication Techniques

Cu(In, Ga)Se2 (CIGS)-based solar cells from six fabricators were characterized and compared. The devices had differing substrates, absorber deposition processes, buffer materials, and contact materials. The effective bandgaps of devices varied from 1.05 to 1.22 eV, with the lowest optical bandgaps occurring in those with metal-precursor absorber processes. Devices with Zn(O, S) or thin CdS buffers had quantum efficiencies above 90% down to 400 nm. Most voltages were 250–300 mV below the Shockley–Queisser limit for their bandgap. Electroluminescence intensity tracked well with the respective voltage deficits. Fill factor (FF) was as high as 95% of the maximum for each device's respective current and voltage, with higher FF corresponding to lower diode quality factors (∼1.3). An in-depth analysis of FF losses determined that diode quality reflected in the quality factor, voltage-dependent photocurrent, and, to a lesser extent, the parasitic resistances are the limiting factors. Different absorber processes and device structures led to a range of electrical and physical characteristics, yet this investigation showed that multiple fabrication pathways could lead to high-quality and high-efficiency solar cells.

A flatter gallium profile for high-efficiency Cu(In,Ga)(Se,S)2 solar cell and improved robustness against sulfur-gradient variation

Co-optimization of the gallium and sulfur profiles in penternary Cu(In,Ga)(Se,S)2 thin film solar cell and its impacts on device performance and variability are investigated in this work. An absorber formation method to modulate the gallium profiling under low sulfur-incorporation is disclosed, which solves the problem of Ga-segregation in selenization. Flatter Ga-profiles, which lack of experimental investigations to date, are explored and an optimal Ga-profile achieving 17.1% conversion efficiency on a 30 cm × 30 cm sub-module without anti-reflection coating is presented. Flatter Ga-profile gives rise to the higher Voc × Jsc by improved bandgap matching to solar spectrum, which is hard to be achieved by the case of Ga-accumulation. However, voltage-induced carrier collection loss is found, as evident from the measured voltage-dependent photocurrent characteristics based on a small-signal circuit model. The simulation results reveal that the loss is attributed to the synergistic effect of the detrimental gallium and sulfur gradients, which can deteriorate the carrier collection especially in quasi-neutral region (QNR). Furthermore, the underlying physics is presented, and it provides a clear physical picture to the empirical trends of device performance, I–V characteristics, and voltage-dependent photocurrent, which cannot be explained by the standard solar circuit model. The parameter “FGa” and front sulfur-gradient are found to play critical roles on the trade-off between space charge region (SCR) recombination and QNR carrier collection. The co-optimized gallium and sulfur gradients are investigated, and the corresponding process modification for further efficiency-enhancement is proposed. In addition, the performance impact of sulfur-gradient variation is studied, and a gallium design for suppressing the sulfur-induced variability is proposed. Device performances of varied Ga-profiles with front sulfur-gradients are simulated based on a compact device model. Finally, an exploratory path toward 20% high-efficiency Ga-profile with robustness against sulfur-induced performance variability is presented.

Fabrication of Cu2ZnSn(S,Se)4 thin film solar cells by selenization of reactively sputtered precursors

Cu2ZnSn(S,Se)4 thin films were fabricated by selenization of reactively sputtered precursors. The precursors showed a fully sulfurized Cu2ZnSnS4 phase with compact surface and columnar structure. The evolutions of composition, morphology and phases for the selenized films were investigated. The selenization resulted in dramatic changes in morphologies, but demonstrated excellent stability on metallic composition and negligible volume expansion of the selenized films. The selenized films show densely packed large grains and single kesterite Cu2ZnSn(S,Se)4 phase. The solar cell with the structure of ITO/i-ZnO/CdS/CZTSSe/Mo/Glass presents the highest power conversion efficiency of 4.3%. The key limitation factor is due to low fill factor, which is mainly caused by a low shunt resistance and severe voltage-dependent photocurrent collection.

Analytical Model for Voltage-Dependent Photo and Dark Currents in Bulk Heterojunction Organic Solar Cells

A physics-based explicit mathematical model for the external voltage-dependent forward dark current in bulk heterojunction (BHJ) organic solar cells is developed by considering Shockley-Read-Hall (SRH) recombination and solving the continuity equations for both electrons and holes. An analytical model for the external voltage-dependent photocurrent in BHJ organic solar cells is also proposed by incorporating exponential photon absorption, dissociation efficiency of bound electron-hole pairs (EHPs), carrier trapping, and carrier drift and diffusion in the photon absorption layer. Modified Braun’s model is used to compute the electric field-dependent dissociation efficiency of the bound EHPs. The overall net current is calculated considering the actual solar spectrum. The mathematical models are verified by comparing the model calculations with various published experimental results. We analyze the effects of the contact properties, blend compositions, charge carrier transport properties (carrier mobility and lifetime), and cell design on the current-voltage characteristics. The power conversion efficiency of BHJ organic solar cells mostly depends on electron transport properties of the acceptor layer. The results of this paper indicate that improvement of charge carrier transport (both mobility and lifetime) and dissociation of bound EHPs in organic blend are critically important to increase the power conversion efficiency of the BHJ solar cells.

High spectral response of self-driven GaN-based detectors by controlling the contact barrier height

High spectral response of self-driven GaN-based ultraviolet detectors with interdigitated finger geometries were realized using interdigitated Schottky and near-ohmic contacts. Ni/GaN/Cr, Ni/GaN/Ag, and Ni/GaN/Ti/Al detectors were designed with zero bias responsivities proportional to the Schottky barrier difference between the interdigitated contacts of 0.037 A/W, 0.083 A/W, and 0.104 A/W, respectively. Voltage-dependent photocurrent was studied, showing high gain under forward bias. Differences between the electron and hole mobility model and the hole trapping model were considered to be the main photocurrent gain mechanism. These detectors operate in photoconductive mode with large photocurrent gain and depletion mode with high speed, and can extend GaN-based metal-semiconductor-metal detector applications.

2,7-Carbazole and thieno[3,4-c]pyrrole-4,6-dione based copolymers with deep highest occupied molecular orbital for photovoltaic cells

Three kinds of donor–acceptor (D–A) type photovoltaic polymers were synthesized based on 2,7-carbazole and thieno[3,4-c]pyrrole-4,6-dione (TPD). The conjugation of weakly electron (e)-donating 2,7-carbazole and strongly e-accepting TPD moieties yielded a deep highest occupied molecular orbital (HOMO) and its energy level was fine-controlled to be −5.72, −5.67 and −5.57 eV through the incorporation of thiophene (T), thieno[3,2-b]thiophene (TT) and bithiophene (BT) as a π-bridge. Polymer:[6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) based bulk heterojunction solar cells exhibited a high open-circuit voltage (VOC) in the range, 0.86–0.94 V, suggesting good agreement with the measured HOMO levels. Despite the high VOC, the thiophene (or thienothiophene)-containing PCTTPD (or PCTTTPD) showed poor power conversion efficiency (PCE, 1.14 and 1.25%) because of the very low short-circuit current density (JSC). The voltage-dependent photocurrent and photoluminescence quenching measurements suggested that hole transfer from PC71BM to polymer depends strongly on the HOMO level of the polymer. The PCTTPD and PCTTTPD devices suffered from electron–hole recombination at the polymer/PC71BM interfaces because of the insufficient energy offset between the HOMOs of the polymer and PC71BM. The PCBTTPD:PC71BM device showed the best PCE of 3.42% with a VOC and JSC of 0.86 V and 7.79 mA cm−2, respectively. These results show that photovoltaic polymers should be designed carefully to have a deep HOMO level for a high VOC and sufficient energy offset for ensuring efficient hole transfer from PC71BM to the polymer.

Correlation of Built-In Potential and I–V Crossover in Thin-Film Solar Cells

Thin-film solar cells often show a crossover between the illuminated and dark I-V characteristics. Several device specific reasons for crossover exist and have been discussed extensively. In this paper, we show that a low contact-to-contact built-in potential can produce a voltage-dependent photocurrent that leads to I-V crossover at a voltage that is almost exactly the device built-in potential. This mechanism can produce crossover in the absence of carrier trapping or recombination. It can be a contributing factor to crossover, but when an anomalously low contact-to-contact built-in potential exists, it can be the dominant factor. Using numerical simulations, we examine a variety of model solar cell structures with low contact-to-contact built-in potential and show a strong correlation of the crossover and built-in potential voltages. These simulations also suggest that a plot of the illuminated minus dark current may help identify when a low V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bi</sub> is limiting device performance.

Correlation of Morphology with Photocurrent Generation in a Polymer Blend Photovoltaic Device

Morphological effects on photovoltaic (PV) properties are studied through scanning photocurrent (PC) and photoluminescence (PL) microscopy of a solution processed, polymer blend PV device composed of PFB [poly(9,9'-dioctylfluorene-co-bis-N,N-(4-butylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine] and F8BT [poly(9,9'-dioctylfluorene-co-benzothiadiazole]. As PFB and F8BT have unique absorbance bands, it is possible to selectively excite only F8BT (488 nm) or both PFB and F8BT (408 nm). Local voltage-dependent photocurrent (LVPC) measurements from particular regions of interest in the PV show that the diode characteristics between different morphologies are essentially the same, except in regard to the magnitude of PC generated. A local PL spectrum is measured simultaneously with PC generation at each pixel in the image maps. Through integration of the local PL spectrum over particular wavelength ranges, PL image maps are created of PFB-PL (435 to 475 nm), F8BT-PL (530 to 570 nm), exciplex-PL (620 to 685 nm) and total-PL (entire spectrum). These data allow direct correlation of PC generation with local chemical composition variations within the PV device. PL image maps show morphological variations on the order of 0.5 to 1 µm of alternating PFB-rich and F8BT-rich phases. While illuminating only F8BT (488 nm light), the PFB-rich phases produce the most PC, however, while illuminating both polymers but mostly PFB (408 nm light), the F8BT-rich phases produce the most PC. These results show that in the morphology where the light absorbing material is less concentrated, the PC generation is increased. Additionally, the exciplex-PL is found to not be a significant radiative loss mechanism of charge carriers for PC generation.