Thin‐Film Solar Cells with InP Absorber Layers Directly Grown on Nonepitaxial Metal Substrates

The design and performance of solar cells based on InP grown by the nonepitaxial thin‐film vapor–liquid–solid (TF‐VLS) growth technique is investigated. The cell structure consists of a Mo back contact, p‐InP absorber layer, n‐TiO₂ electron selective contact, and indium tin oxide transparent top electrode. An ex situ p‐doping process for TF‐VLS grown InP is introduced. Properties of the cells such as optoelectronic uniformity and electrical behavior of grain boundaries are examined. The power conversion efficiency of first generation cells reaches 12.1% under simulated 1 sun illumination with open‐circuit voltage (V_OC) of 692 mV, short‐circuit current (J_SC) of 26.9 mA cm^?2, and fill factor (FF) of 65%. The FF of the cell is limited by the series resistances in the device, including the top contact, which can be mitigated in the future through device optimization. The highest measured V_OC under 1 sun is 692 mV, which approaches the optically implied V_OC of ≈795 mV extracted from the luminescence yield of p‐InP.     

Efficient Vacuum‐Deposited Tandem Organic Solar Cells with Fill Factors Higher Than Single‐Junction Subcells

Efficient vacuum‐deposited tandem organic photovoltaic cells (TOPVs) composed of pristine fullerenes as the acceptors and two complementary absorbing donors, 2‐((2‐(5‐(4‐(diphenylamino)phenyl)thieno[3,2‐b]thiophen‐2‐yl)thiazol‐5‐yl)methylene)malononitrile for the visible absorption and 2‐((7‐(5‐(dip‐tolylamino)thiophen‐2‐yl)benzo[c]‐[1,2,5]thiadiazol‐4‐yl)methylene)malononitrile for the near‐infrared absorption, are reported. Two subcells are connected by the interconnection unit (ICU) composed of electron‐transporting layer/metal/p‐doped hole‐transporting layer. The p‐doped layer in the ICU enables increasing the short‐circuit current density (J _SC) of TOPVs by tuning the relative position of subcells in the tandem devices to have the maximum optical field distribution response, which is well matched with theoretical calculation. Moreover, the introduction of the doped layer benefits to the higher fill factor (FF) of the consisting subcells without losing open‐circuit voltage (V _OC) even with the thick active layers. As a result, power conversion efficiency of 9.2% is achieved with higher FF of 0.62 than that of single‐junction subcells (0.54, 0.57), J _SC of 8.7 mA cm^?2, and V _OC of 1.71 V using 80 nm thick active layers in both subcells.     

Identifying the Impact of Surface Recombination at Electrodes in Organic Solar Cells by Means of Electroluminescence and Modeling

This work reports on combining current‐voltage characteristics, electroluminescence (EL) measurements, and modeling to identify the selectivity of the electrodes in bulk‐heterojunction organic solar cells. Devices with the same photoactive layer but different contact materials are compared and the impact of surface recombination at the contacts on their performance is determined. The open‐circuit voltage, V _OC, depends strongly on the selectivity of the electrodes and it is observed that the EL signal of cells with lower V _OC is dramatically reduced. This is ascribed to an enhanced rate of surface recombination, which is a non‐radiative recombination pathway and does therefore not contribute to the EL yield. In addition, these cells have a lower current in forward direction despite the fact that the surface recombination occurs in addition to the recombination in the bulk. A theoretical model was set up and in the corresponding numerical simulations all three findings (lower V _OC, strongly reduced EL signal and lower forward current) could be clearly reproduced by varying just one single parameter which determines the selectivity of the electrode.     

Solution Processable Inorganic–Organic Double‐Layered Hole Transport Layer for Highly Stable Planar Perovskite Solar Cells

Perovskite solar cells (PSCs) have reached their highest efficiency with 2,2′,7,7′‐tetrakis(N,N′‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐OMeTAD). However, this material can cause problems with respect to reproducibility and stability. Herein, a solution‐processable inorganic–organic double layer based on tungsten oxide (WO₃) and spiro‐OMeTAD is reported as a hole transport layer in PSCs. The device equipped with a WO₃/spiro‐OMeTAD layer achieves the highest efficiency (21.44%) in the tin (IV) oxide planar structure. The electronic properties of the double layer are thoroughly analyzed using photoluminescence, space‐charge–limited current, and electrochemical impedance spectroscopy. The WO₃/spiro‐OMeTAD layer exhibits better hole extraction ability and faster hole mobility. The WO₃ layer particularly improves the open‐circuit voltage (V_OC) by lowering the quasi‐Fermi energy level for holes and reducing charge recombination, resulting in high V_OC (1.17 V in the champion cell). In addition, the WO₃ layer as a scaffold layer promotes the formation of a uniform and pinhole‐free spiro‐OMeTAD overlayer in the WO₃/spiro‐OMeTAD layer. High stability under thermal and humid conditions stems from this property. The study presents a facile approach for improving the efficiency and stability of PSCs by stacking an organic layer on an inorganic layer.     

Evaluation of Built‐In Potential and Loss Mechanisms at Contacts in Organic Solar Cells: Device Model Parameterization,Validation, and Prediction

Maximizing the power conversion efficiency of organic solar cells requires the simultaneous optimization of its short‐circuit current density, fill factor, and open‐circuit voltage V_oc. Several key parameters of the device model needed to understand these quantities have not been reliably determined, even for the prototypical poly(3‐hexylthiophene):phenyl‐C₆₁‐methylbutyric ester (P3HT:PCBM) photoactive layer (PAL). Detailed analysis of the loss mechanisms at contacts and their rational optimization have not been possible. Here, using crosslinked P3HT network:PCBM cells with predefined ultrafine donor–acceptor morphology and very high internal quantum efficiencies, the built‐in potential V_bi is measured to decouple and reliably extract other key parameters of the cells. Using the refined device parameters, the general optimization of organic solar cells is evaluated and the following is established: i) The PAL composition of the first optical absorption optimum is displaced towards the more strongly absorbing component due to thin film effects. ii) The optimal cell configuration is the one in which the slower carrier travels on average the shorter distance to the collection contact, a consequence of the asymmetric photogeneration profile. iii) The absorption thickness optima follows a simple λ_p/n_PAL scaling law, where λ_p is its absorption center wavelength and n_PAL is the corresponding refractive index.     

Light‐Induced Degradation of Polymer:Fullerene Photovoltaic Devices: An Intrinsic or Material‐Dependent Failure Mechanism?

Although degradation mechanisms in organic photovoltaic devices continue to receive increased attention, it is only recently that the initial light‐induced failure, or so‐called burn‐in effect, has been considered. Both prototypical polythiophene:fullerene and polycarbazole:fullerene systems exhibit an exponential performance loss of ≈40% upon 150 h of continuous solar illumination. While the decrease in both the short‐circuit current (J_SC) and open‐circuit voltage (V_OC) is the origin of performance loss in poly(3‐hexylthiophene):[6,6]‐phenyl‐C61‐butyric acid methyl ester (P3HT:PC₆₀BM), in poly(N‐9′‐hepta‐decanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)):[6,6]‐phenyl‐C71‐butyric acid methyl ester (PCDTBT:PC₇₀BM) the decline of the fill factor dominates. By systematic variation of the interface layers, active layer thickness, and acceptor in polythiophene:fullerene cells, the loss in J_SC is ascribed to a degradation in the bulk of the P3HT:PC₆₀BM, while the drop in V_OC is reversible and arises from charge trapping at the contact interfaces. By replacing the C₆₀ fullerene derivative with a C₇₀ derivative, or by modifying the electron transport layer, the J_SC or V_OC, respectively, are stabilized. These insights prove that the burn‐in process stems from multiple concurrent failure mechanisms. Comparing the ageing and recovery processes in P3HT and PCDTBT blends results in the conclusion that their interface failures differ in nature and that burn‐in is a material dependent, rather than an intrinsic, failure mechanism.     

Achieving High Open‐Circuit Voltages up to 1.57 V in Hole‐Transport‐Material‐Free MAPbBr3 Solar Cells with Carbon Electrodes

An open‐circuit voltage (V_oc) of 1.57 V under simulated AM1.5 sunlight in planar MAPbBr₃ solar cells with carbon (graphite) electrodes is obtained. The hole‐transport‐material‐free MAPbBr₃ solar cells with the normal architecture (FTO/TiO₂/MAPbBr₃/carbon) show little hysteresis during current–voltage sweep under simulated AM1.5 sunlight. A solar‐to‐electricity power conversion efficiency of 8.70% is achieved with the champion device. Accordingly, it is proposed that the carbon electrodes are effective to extract photogenerated holes in MAPbBr₃ solar cells, and the industry‐applicable carbon electrodes will not limit the performance of bromide‐based perovskite solar cells. Based on the analysis of the band alignment, it is found that the voltage (energy) loss across the interface between MAPbBr₃ and carbon is very small compared to the offset between the valence band maximum of MAPbBr₃ and the work function of graphite. This finding implies either Fermi level pinning or highly doped region inside MAPbBr₃ layer exists. The band‐edge electroluminescence spectra of MAPbBr₃ from the solar cells further support no back‐transfer pathways of electrons across the MAPbBr₃/TiO₂ interface.     

Enhanced Light Harvesting in Perovskite Solar Cells by a Bioinspired Nanostructured Back Electrode

Light management holds great promise of realizing high‐performance perovskite solar cells by improving the sunlight absorption with lower recombination current and thus higher power conversion efficiency (PCE). Here, a convenient and scalable light trapping scheme is demonstrated by incorporating bioinspired moth‐eye nanostructures into the metal back electrode via soft imprinting technique to enhance the light harvesting in organic–inorganic lead halide perovskite solar cells. Compared to the flat reference cell with a methylammonium lead halide perovskite (CH₃NH₃PbI_3?x Cl_x ) absorber, 14.3% of short‐circuit current improvement is achieved for the patterned devices with moth‐eye nanostructures, yielding an increased PCE up to 16.31% without sacrificing the open‐circuit voltage and fill factor. The experimental and theoretical characterizations verify that the cell performance enhancement is mainly ascribed by the broadband polarization‐insensitive light scattering and surface plasmonic effects due to the patterned metal back electrode. It is noteworthy that this light trapping strategy is fully compatible with solution‐processed perovskite solar cells and opens up many opportunities toward the future photovoltaic applications.     

Loss Mechanisms in High Efficiency Polymer Solar Cells

Performance losses and aging mechanisms are investigated in state‐of‐the‐art PTB7:PC₇₀BM solar cells. Inverted devices incorporating a vanadium pentoxide (V₂O₅) top contact have efficiencies of 8%. After aging the unencapsulated devices, no changes are observed in the open circuit voltage (V_oc) or short circuit current (J_sc); however, the fill factor (FF) drops from 0.7 to 0.61. An s‐shape initially appears in the J–V curve after aging, which can be reduced by cycling through the J–V curve under illumination. This is discussed in context of the redox properties of V₂O₅. With impedance spectroscopy, it is demonstrated that changes to the contact interfaces are completely reversible and not responsible for the performance loss. Intensity modulated photocurrent spectroscopy combined with device modeling reveals that the loss in FF is due to trap formation in the active layer. Additionally it is observed that the performance of pristine devices is limited by optical absorption in the thin active layer and the build‐up of space charge which hinders carrier extraction.     

Efficient,Cyanine Dye Based Bilayer Solar Cells

Simple bilayer solar cells, using commercially available cationic cyanine dyes as donors and evaporated C₆₀ layer as an acceptor are prepared. Cyanine dyes with absorption maxima of 578, 615 and 697 nm having either perchlorate or hexafluorophosphate counter‐ions are evaluated. The perchlorate dye leads to cells with S‐shape current‐voltage curves; only the dyes with the hexafluorophosphate counter‐ions lead to efficient solar cells. When the wide bandgap dyes are employed, S‐shape current‐voltage curves are obtained when the conductive polymer PEDOT:PSS is used as hole transport layer. Substitution of PEDOT:PSS with MoO₃ leads to cells with more rectangular current–voltage curves and high fill factors. Additionally, the cells using the MoO₃ layer for hole extraction lead to high open circuit voltages of 0.9 V. In the case that a low bandgap hexafluorophosphate dye is used with the HOMO above that of the PEDOT:PSS the cell performance is independent on the type of hole transport layer employed. Using this approach, bilayer solar cells are obtained with power efficiencies ranging from 1.8 to 2.9% depending on the particular dye employed. These are impressive numbers for bilayer solar cell that are partially solution processed in ambient conditions.     

Lessons Learnt from Spatially Resolved Electro‐ and Photoluminescence Imaging: Interfacial Delamination in CH3NH3PbI3 Planar Perovskite Solar Cells upon Illumination

The influence of illumination on the long‐term performance of planar structured perovskite solar cells (PSCs) is investigated using fast and spatially resolved luminescence imaging. The authors analyze the effect of illuminated current density–voltage (J–V) and light‐soaking measurements on pristine PSCs by providing visual evidence for the spatial inhomogeneous evolution of device performance. Regions that are exposed to light initially produce stronger electroluminescence signals than surrounding unilluminated regions, mainly due to a lower contact resistance and, possibly, higher charge collection efficiency. Over a period of several days, however, these initially illuminated regions appear to degrade more quickly despite the device being stored in a dark, moisture‐ and oxygen‐free environment. Using transmission electron microscopy, this accelerated degradation is attributed to delamination between the perovskite and the titanium dioxide (TiO₂) layer. An ion migration mechanism is proposed for this delamination process, which is in accordance with previous current–voltage hysteresis observations. These results provide evidence for the intrinsic instability of CH₃NH₃PbI₃‐based devices under illumination and have major implications for the design of PSCs from the standpoint of long‐term performance and stability.     

Ultra‐High Voltage Multijunction Organic Solar Cells for Low‐Power Electronic Applications

Low power electronics are an ideal application for organic photovoltaics (OPV) where a low‐cost OPV device can be integrated directly with a battery to provide a constant power source. We demonstrate ultra‐high voltage small molecule multijunction devices with open circuit voltage (V_OC) values of up to 7V. Optical modelling is employed to aid the optimisation of the complex multi‐layer stacks and ensure current balancing is achieved between sub‐cells, and optimised multijunction devices show power conversion efficiencies of up to 3.4% which is a modest increase over the single junction devices. Sub‐cell donor/acceptor pairs of boron subphthalocyanine chloride (SubPc)/fullerene (C₆₀) and SubPc/Cl₆‐SubPc were selected both for their high V_OC in order to minimise the required number of junctions, but also for their absorption overlap to reduce the spectral dependence of the device performance. As a result, the devices are shown to directly charge a micro‐energy cell type battery under both low illumination intensity white light and monochromatic illumination.     

Light‐Induced Degradation Mechanism in Poly(3‐hexylthiophene)/Fullerene Blend Solar Cells

The mechanism of light‐induced degradation in organic solar cells based on regioregular poly(3‐hexylthiophene) and indene‐C₆₀ bisadduct is studied by transient absorption (TA) and electron spin resonance (ESR) measurements. After 45 h light exposure under simulated solar illumination at 100 mW cm^?2, the short‐circuit current density, open‐circuit voltage, and fill factor are all degraded by about 20%–30% relative to the initial photovoltaic parameters. For the assignment of limiting conversion processes in the degraded solar cells, exciton diffusion into a donor/acceptor interface, charge transfer at the interface, charge dissociation into free charge carriers, and charge collection to each electrode are observed before and after the light exposure by the TA measurement. As a result, it is found that the charge collection deteriorates after the light exposure because of light‐induced charge trap formation in the bulk of the active layer. The origin of charge traps is further discussed on the basis of ESR measurements and density functional theory calculation.     

Solution‐Processed Hydrogen Molybdenum Bronzes as Highly Conductive Anode Interlayers in Efficient Organic Photovoltaics

Highly efficient and stable organic photovoltaic (OPV) cells are demonstrated by incorporating solution‐processed hydrogen molybdenum bronzes as anode interlayers. The bronzes are synthesized using a sol‐gel method with the critical step being the partial oxide reduction/hydrogenation using an alcohol‐based solvent. Their composition, stoichiometry, and electronic properties strongly correlate with the annealing process to which the films are subjected after spin coating. Hydrogen molybdenum bronzes with moderate degree of reduction are found to be highly advantageous when used as anode interlayers in OPVs, as they maintain a high work function similar to the fully stoichiometric metal oxide, whereas they exhibit a high density of occupied gap states, which are beneficial for charge transport. Enhanced short‐circuit current, open‐circuit voltage and, fill factor, relative to reference devices incorporating either PEDOT‐PSS or a solution processed stoichiometric molybdenum oxide, are obtained for a variety of bulk heterojunction mixtures based on different polymeric donors and fullerene acceptors. In particular, high power conversion efficiencies are obtained in devices that employed the s‐H_xMoO_2.75 as the hole extraction layer.     

A New Interconnecting Layer of Metal Oxide/Dipole Layer/Metal Oxide for Efficient Tandem Organic Solar Cells

A new metal‐oxide‐based interconnecting layer (ICL) structure of all‐solution processed metal oxide/dipole layer/metal oxide for efficient tandem organic solar cell (OSC) is demonstrated. The dipole layer modifies the work function (WF) of molybdenum oxide (MoO _x ) to eliminate preexisted counter diode between MoO _x and TiO₂. Three different amino functionalized water/alcohol soluble conjugated polymers (WSCPs) are studied to show that the WF tuning of MoO _x is controllable. Importantly, the results show that S‐shape current density versus voltage (J–V) characteristics form when operation temperature decreases. This implies that thermionic emission within the dipole layer plays critical role for helping recombination of electrons and holes. Meanwhile, the insignificant homotandem open‐circuit voltage (V _oc) loss dependence on dipole layer thickness shows that the quantum tunneling effect is weak for efficient electron and hole recombination. Based on this ICL, poly(3‐hexylthiophene) (P3HT)‐based homotandem OSC with 1.20 V V _oc and 3.29% power conversion efficiency (PCE) is achieved. Furthermore, high efficiency poly(4,8‐bis(5‐(2‐ethylhexyl)‐thiophene‐2‐yl)‐benzo[1,2‐b54,5‐b9]dithiophene‐alt alkylcarbonylthieno[3,4‐b]thiophene) (PBDTTT‐C‐T)‐based homotandem OSC with 1.54 V V _oc and 8.11% PCE is achieved, with almost 15.53% enhancement compared to its single cell. This metal oxide/dipole layer/metal oxide ICL provides a new strategy to develop other qualified ICL with different hole transporting layer and electron transporting layer in tandem OSCs.     

Hybrid Perovskite‐Organic Flexible Tandem Solar Cell Enabling Highly Efficient Electrocatalysis Overall Water Splitting

Perovskite‐organic tandem solar cells are attracting more attention due to their potential for highly efficient and flexible photovoltaic device. In this work, efficient perovskite‐organic monolithic tandem solar cells integrating the wide bandgap perovskite (1.74 eV) and low bandgap organic active PBDB‐T:SN6IC‐4F (1.30 eV) layer, which serve as the top and bottom subcell, respectively, are developed. The resulting perovskite‐organic tandem solar cells with passivated wide‐bandgap perovskite show a remarkable power conversion efficiency (PCE) of 15.13%, with an open‐circuit voltage (V_oc) of 1.85 V, a short‐circuit photocurrent (J_sc) of 11.52 mA cm^?2, and a fill factor (FF) of 70.98%. Thanks to the advantages of low temperature fabrication processes and the flexibility properties of the device, a flexible tandem solar cell which obtain a PCE of 13.61%, with V_oc of 1.80 V, J_sc of 11.07 mA cm^?2, and FF of 68.31% is fabricated. Moreover, to demonstrate the achieved high V_oc in the tandem solar cells for potential applications, a photovoltaic (PV)‐driven electrolysis system combing the tandem solar cell and water splitting electrocatalysis is assembled. The integrated device demonstrates a solar‐to‐hydrogen efficiency of 12.30% and 11.21% for rigid, and flexible perovskite‐organic tandem solar cell based PV‐driven electrolysis systems, respectively.     

Simultaneous Improvement of Photovoltaic Performance and Stability by In Situ Formation of 2D Perovskite at (FAPbI3)0.88(CsPbBr3)0.12/CuSCN Interface

To solve the stability issues of perovskite solar cells (PSC), here a novel interface engineering strategy that a versatile ultrathin 2D perovskite (5‐AVA)₂PbI₄ (5‐AVA = 5‐ammoniumvaleric acid) passivation layer that is in situ incorporated at the interface between (FAPbI₃)_0.88(CsPbBr₃)_0.12 and the hole transporting CuSCN is reported. Surface analysis using X‐ray photoelectron spectroscopy confirms the formation of 2D perovskite. Hysteresis is reduced by the interfacial 2D layer, which could be ascribed to improvement of interfacial charge extraction efficiency, associated with suppression of recombination. Moreover, introduction of the interface passivating layer enhances the moisture stability and photostability as compared to the control perovskite film due to hydrophobic nature of 2D perovskite. The unencapsulated device retains 98% of the initial power conversion efficiency (PCE) after 63 d under moisture exposure of about 10% in the dark. A PCE of the control device is boosted from 13.72 to 16.75% as a consequence of enhanced open‐circuit voltage (V_oc) and fill factor along with slightly increased short‐circuit current density (J_sc), which results from reduced trap states of (FAPbI₃)_0.88(CsPbBr₃)_0.12 as evidenced by enhanced carrier lifetimes and charge extraction. The perovskite/hole transport material interface engineering gives insight into simultaneous improvements of PCE and device stability.     

Decreased Recombination Through the Use of a Non‐Fullerene Acceptor in a 6.4% Efficient Organic Planar Heterojunction Solar Cell

An optimization of several aspects of planar heterojunction solar cells based on boron subnaphthalocyanine chloride (SubNc) as a donor material is presented. The use of hexachlorinated boron subphthalocyanine chloride (Cl₆SubPc) as an alternative acceptor to C₆₀ allows for the simultaneous increase of the short‐circuit current, fill factor, and open‐circuit voltage compared to cells with fullerene acceptors. This is due to the complementary absorption of Cl₆SubPc versus SubNc, reduced recombination at the heterointerface, and improved energetic alignment. Furthermore, insertion of a thin diindeno[1,2,3‐cd:1′,2′,3′‐lm]perylene (DIP) layer at the anode results in a very significant 60% increase in photocurrent owing to reduced exciton quenching at the anode. The simultaneous improvement of all three solar cell para­meters results in a power conversion efficiency of 6.4% for a non‐fullerene planar heterojunction cell.     

Investigation of Charge Carrier Behavior in High Performance Ternary Blend Polymer Solar Cells

This study demonstrates high‐performance, ternary‐blend polymer solar cells by modifying a binary blend bulk heterojunction (PPDT2FBT:PC₇₁BM) with the addition of a ternary component, PPDT2CNBT. PPDT2CNBT is designed to have complementary absorption and deeper frontier energy levels compared to PPDT2FBT, while being based on the same polymeric backbone. A power conversion efficiency of 9.46% is achieved via improvements in both short‐circuit current density (J_SC) and open‐circuit voltage (V_OC). Interestingly, the V_OC increases with increasing the PPDT2CNBT content in ternary blends. In‐depth studies using ultraviolet photoelectron spectroscopy and transient absorption spectroscopy indicate that the two polymers are not electronically homogeneous and function as discrete light harvesting species. The structural similarity between PPDT2CNBT and PPDT2FBT allows the merits of a ternary system to be fully utilized to enhance both J_SC and V_OC without detriment to fill‐factor via minimized disruption of semi‐crystalline morphology of binary PPDT2FBT:PC₇₁BM blend. Further, by careful analysis, charge carrier transport in this ternary blend is clearly verified to follow parallel‐like behavior.     

Dithienogermole‐Containing Small‐Molecule Solar Cells with 7.3% Efficiency: In‐Depth Study on the Effects of Heteroatom Substitution of Si with Ge

Two small molecule donor materials (DTGe(FBTTh₂)₂ and DTGe(FBTBFu)₂) incorporating the dithienogermole (DTGe) moiety with fluorobenzothiadiazole (FBT) and bithiophene (Th₂) or benzofuran (BFu) end‐capping groups are synthesized and their properties as donor materials in small molecule bulk heterojunction type (BHJ) solar cells are investigated. The DTGe(FBTTh₂)₂ with Th₂ end groups shows outstanding solar cell characteristics with efficiencies up to 6.4% using a standard BHJ architecture and 7.3% using a ZnO optical spacer, while the BFu end‐capped DTGe(FBTBFu)₂ has slightly wider band gaps and yields slightly higher open circuit voltage (V_OC) at the expense of short circuit current (J_SC) and fill factor (FF). In this study, the DTGe‐based molecules are systematically compared to the dithienosilole (DTSi)‐based analogues, which are currently among the highest power conversion efficiency (PCE) small molecule solar cell donor materials known. The J_SC produced by the DTGe molecule is found to be similar to, or slightly higher than the Si analogue, despite similar absorption characteristics, however, the PCE is similar to the Si analogues due to small decreases in V_OC and FF. This report marks the first small molecule BHJ based on a Ge‐containing heterocycle with PCE over 7%.