Fill Factor Losses and Deviations from the Superposition Principle in Lead Halide Perovskite Solar Cells

Abstract

The enhancement of the fill factor in the current generation of perovskite solar cells is the key for further efficiency improvement. Thus, methods to quantify the fill factor losses are urgently needed. Two methods are presented to quantify losses due to the finite resistance of the semiconducting layers of the solar cell as well as its contacts. The first method is based on the comparison between the voltage in the dark and under illumination analyzed at equal recombination current density and results in a voltage‐dependent series resistance. Furthermore, the method reveals the existence of a strong photoshunt under illumination. The second method is based on measuring the photoluminescence of perovskite solar cells as a function of applied voltage. Thereby, the recombination current is determined as a function of voltage from short circuit to open circuit, and the presence of the photoshunt is explained with a high resistance of the electron and/or hole transport layers combined with field screening in the absorber.

Understanding the Thickness and Light-Intensity Dependent Performance of Green-Solvent Processed Organic Solar Cells

“…A simple way to distinguish between the ideal case with a voltage-independent photocurrent ( J sc ) and the nonideal case with a voltage-dependent photocurrent J ph is to plot the sum J ( V , Φ) + J sc (Φ) (with J sc > 0), which is depicted in Figure a–c for different thicknesses and illumination intensities. This approach of shifting the light J – V curves into the first quadrant and plotting them logarithmically has been infrequently used in various photovoltaic technologies ,,,, starting with Si in the late 1970s but has so far not been discussed in the context of organic photovoltaics. The shifted J – V curve resembles a dark J – V curve and represents the deviation from the voltage-independent ideal case J ( V , Φ) + J sc (Φ) = J d ( V ) – ( J ph ( V , Φ) – J sc (Φ)) = J d ( V ) – Δ J ph ( V , Φ), where J ph > 0 and Δ J ph < 0.…”

Device Performance of Emerging Photovoltaic Materials (Version 3)

“…While the fill factor of halide perovskites with typical bandgaps in the range ≈1.6 eV could exceed 90% in the detailed balance limit, in practice reported fill factors were mostly in the range of 80% to 84% for the best devices. [ 18 ] Recently, however, strategies based on interface modifications were reported to improve the fill factor up to 86% even for areas >1 cm 2 while at the same time enabling high efficiencies above 23%. [ 19 ] Also in the field of higher bandgap p–i–n type perovskite solar cells, high fill factors above 86% were achieved by interfacial passivation with guanidinium bromide.…”

Ideality Factor Mapping of Back‐Contact Perovskite Solar Cells

“…From the Suns‐ V oc and Suns‐PL analysis, it is straight‐forward to produce pseudo‐ J ‐ V curves and to calculate the corresponding pseudo‐fill factor (pFF) and pseudo‐maximum power point ( pP max ) of these curves. [ 36–38 ] While SQ analysis defines the upper limit of the FF and maximum power point ( P max ) by considering only radiative recombination losses, the pP max and pFF provide a measure of the highest possible values that could be achieved with the current level of non‐radiative recombination without the influence of series resistance or transport losses. Another useful parameter is the charge collection efficiency $$\frac{{{J_{{\rm{SC,i}}}}}}{{{J_{\rm{L}}}}}$$ which defines the probability that photogenerated electron‐hole pairs will dissociate and transport to the electrodes.…”

“…This can be extended to compare ϕ i at each pixel to the mean PL intensity $$\overline {{\phi _i}} $$, $$dQFL{S_i} = \;kT\ln \left( {\frac{{{\phi _i}}}{{\overline {{\phi _i}} }}} \right)$$ in order to produce a relative QFLS map. By applying the common assumption that at steady state (indicated by subscript SS) $$\overline {QFL{S_{{\rm{i,SS}}\;}}} $$ = qV OC,SS [ 36,42,43 ] and add the relative QFLS to each pixel, the local QFLS is given by, $$\[ \begin{array}{*{20}{c}}{QFL{S_i} = q{V_{{\rm{OC,}}\;{\rm{SS}}}}\; + kT\ln \left( {\frac{{{\phi _i}}}{{\overline {{\phi _{{\rm{i,SS}}}}} }}} \right)}\end{array} \]$$…”

“…The pFF and pP max analysis used here has been described in detail by others. [ 36–38 ] The parameters are calculated using an explicit analytical solution which is derived in the Supporting Information. The general approach for the voltage‐related parameters is to use the definition of the ideality factor in Equation (2) to define the change in V OC from a reference value V ref measured at a corresponding reference photocurrent density J L,ref , $$\[ \begin{array}{*{20}{c}}{{V_{{\rm{OC}}}} = {V_{{\rm{Ref}}}}\; + n{V_{\rm{t}}}\ln \left( {\frac{{{J_{\rm{L}}}}}{{{J_{{\rm{L}},{\rm{ref}}}}}}} \right)}\end{array} \]$$…”