Non-fullerene Polymer Solar Cells Research Articles

Nonfullerene Polymer Solar Cells Based on a Main-Chain Twisted Low-Bandgap Acceptor with Power Conversion Efficiency of 13.2%

A new acceptor–donor–acceptor-structured nonfullerene acceptor, 2,2′-((2Z,2′Z)-(((4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(4-((2-ethylhexyl)oxy)thiophene-4,3-diyl))bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (i-IEICO-4F), is designed and synthesized via main-chain substituting position modification of 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)dimalononitrile. Unlike its planar analogue IEICO-4F with strong absorption in the near-infrared region, i-IEICO-4F exhibits a twisted main-chain configuration, resulting in 164 nm blue shifts and leading to complementary absorption with the wide-bandgap polymer (J52). A high solution molar extinction coefficient of 2.41 × 105 M–1 cm–1, and sufficiently high energy of charge-transfer excitons of 1.15 eV in a J52:i-IEICO-4F blend were observed, in comparison with those of 2.26 × 105 M–1 cm–1 and 1.08 eV for IEICO-4F. A power conversion efficiency of...

A new wide-bandgap conjugated polymer based on imide-fused benzotriazole for highly efficient nonfullerene polymer solar cells

A new imide-fused benzotriazole-based conjugated polymer, PBDTS-TzBI, was designed and synthesized via the introduction of alkylthio side chains. The optical, electrochemical and photovoltaic properties of the polymer were well characterized. PBDTS-TzBI exhibits a strong absorption in the range of 400–650 nm with a wide optical bandgap of 1.80 eV and possesses a deep-lying highest occupied molecular orbital energy level of −5.39 eV. Additive-free non-fullerene polymer solar cell (PSC) devices employing PBDTS-TzBI as electron donor and ITIC-Th as electron acceptor delivered an outstanding power conversion efficiency of 9.67% with a high open-circuit voltage of 0.91 V, which is among the best ITIC-Th-based non-fullerene PSC devices so far. This work indicates that the copolymer PBDTS-TzBI is a very promising alternative polymeric donor for highly efficient non-fullerene polymer solar cells.

Synthesis of Conjugated Wide-Bandgap Copolymers Bearing Ladder-Type Donating Units and Their Application to Non-Fullerene Polymer Solar Cells

Two new wide-bandgap conjugated copolymers, T-3MT and 2T-3MT, containing methyl-3-thiophenecarboxylate (3MT) as a weak accepting unit and indacenodithiophene (IDT) or indacenodithienothiophene (IDTT) as ladder-type donating units, were synthesized through Stille coupling polymerization. The effects of the IDT and IDTT units on the physical, optical, and electrochemical properties of these copolymers were investigated. Polymer solar cells (PSCs) were constructed using these new copolymers and different acceptor molecules for inter-comparative analysis of their performance. The PSCs bearing the as-cast active layers with 2,2′-((2Z,2′Z)-((4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b′] dithiophene-2,7-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IM-IDT) displayed the highest PCEs of 3.78−3.96%, mainly owing to the predominant face-on orientation of blend film, and the relatively high open circuit voltage exceeding 1.0 V.

Highly Efficient Nonfullerene Polymer Solar Cells Enabled by a Copper(I) Coordination Strategy Employing a 1,3,4-Oxadiazole-Containing Wide-Bandgap Copolymer Donor.

A novel wide-bandgap copolymer of PBDT-ODZ based on benzo[1,2-b:4,5-b' ]dithiophene (BDT) and 1,3,4-oxadiazole (ODZ) blocks is developed for efficient nonfullerene polymer solar cells (NF-PSCs). PBDT-ODZ exhibits a wide bandgap of 2.12 eV and a low-lying highest occupied molecular orbital (HOMO) level of -5.68 eV, which could match well with the low-bandgap acceptor of 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylthienyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']-dithiophene (ITIC-Th), inducing a good complementary absorption from 300 to 800 nm and a minimal HOMO level offset (0.1 eV). The PBDT-ODZ:ITIC-Th devices exhibit a large open-circuit voltage (Voc ) of 1.08 eV and a low energy loss (Eloss ) of 0.50 eV, delivering a high power conversion efficiency (PCE) of 10.12%. By adding a small amount of copper(I) iodide (CuI) as an additive to form coordination complexes in the active blends, much higher device performances are achieved due to the improved absorption and crystallinity. After incorporating 4% of CuI, the PCE is elevated to 12.34%, with a Voc of 1.06 V, a Jsc of 17.1 mA cm-2 and a fill factor of 68.1%. This work not only provides a novel oxadiazole-containing wide-bandgap polymeric donor candidate for high-performance NF-PSCs but also presents an efficient morphology-optimization approach to elevate the PCE of NF-PSCs for future practical applications.

Asymmetrical Ladder-Type Donor-Induced Polar Small Molecule Acceptor to Promote Fill Factors Approaching 77% for High-Performance Nonfullerene Polymer Solar Cells.

In this work, an effectual strategy of constructing polar small molecule acceptors (SMAs) to promote fill factor (FF) of nonfullerene polymer solar cells (PSCs) is first reported. Three asymmetrical SMAs of IDT6CN, IDT6CN-Th, and IDT6CN-M, which own large dipole moments, are designed and synthesized. The PSCs based on three polar SMAs exhibit apparently higher FFs compared with their symmetrical analogues. The asymmetrical design strategy accompanied with side chain and end group engineering makes IDT6CN-Th- and IDT6CN-M-based nonfullerene PSCs achieve high power conversion efficiency with FFs approaching 77%.

High-Efficiency All Polymer Solar Cell with a Low Voltage Loss of 0.56 V

Reducing voltage loss, namely, Vloss, has been demonstrated to be an effective way to improve the efficiencies of photovoltaic devices, and power conversion efficiencies (PCEs) exceeding 10% have been reported in non-fullerene based polymer solar cells (PSCs) with Vloss value lower than 0.6 V. However, for all polymer solar cells (APSCs), the PCEs lag far behind the non-fullerene PSCs with organic small molecular acceptors. And there have been no successful examples of high-efficiency APSCs along with low Vloss values so far. Here, we reported APSCs that demonstrated a high efficiency of 6.66% simultaneously with a small voltage loss of 0.56 V by using a new polymer PBDT-DFQX1 as donor and N2200 as acceptor. Notably, when PBDT-DFQX1 is combined with a small molecular acceptor (SMA) O-IDTBR, the relative SMA based PSC exhibited a higher PCE of 8.76% also with a low voltage loss of 0.56 V. These results indicated that PBDT-DFQX1 would be a promising polymer donor material in photovoltaic device application,...

An Asymmetrical Polymer Based on Thieno[2,3-f]benzofuran for Efficient Fullerene-Free Polymer Solar Cells

A novel conjugated D–A polymer, PTBFBz, with asymmetrical thieno[2,3-f]benzofuran (TBF) and fluorobenzotriazole (Bz) units was designed and synthesized for the first time. PTBFBz showed the strong absorption with a wide bandgap of 1.89 eV. Power conversion efficiency of nonfullerene polymer solar cells based on PTBFBz:ITIC with thermal and sequential solvent annealing reached up to 8.33%, which is the highest reported value among the asymmetrical TBF-based polymer solar cells. The results demonstrate that the asymmetrical TBF unit can be one of the most promising building blocks in constructing the wide bandgap polymers for highly efficient polymer solar cells.

High‐performing random terpolymer‐based nonfullerene polymer solar cells fabricated using solvent additive‐free as‐cast blend films

ABSTRACTTwo new random terpolymers containing 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDT) as a donating unit, methyl‐3‐thiophenecarboxylate (3MT) as a weak accepting unit, and the more electron‐deficient benzo[c][1,2,5]thiadiazole (BTz) or 5,5′‐bis(2‐ethylhexyl)‐4H,4′H‐1,1′‐bithieno[3,4‐c]pyrrole‐4,4′,6,6′(5H,5′H)‐tetraone (BiTPD) unit as a third monomer (respectively yielding 3MTB and 3MTT) were synthesized in order to achieve improved physical and optoelectronic properties relative to the 3MT‐Th copolymer bearing only BDT and 3MT. The UV–vis absorption spectra and optical bandgap energies of these terpolymers were broader and smaller than those of the 3MT‐Th copolymer. In thin films, the terpolymers displayed the face‐on polymer chain orientation, indicating that the BTz or BiTPD unit in the terpolymer backbones did not affect the molecular arrangement on the substrate. In comparison with 3MT‐Th‐based polymer solar cells (PSCs) as control devices, the PSCs employing blend films of these terpolymers as the donor and 2,2′‐[[6,6,12,12‐Tetrakis(4‐hexylphenyl)‐6,12‐dihydrodithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,8‐diyl]bis[methylidyne(3‐oxo‐1H‐indene‐2,1(3H)‐diylidene)]]bis[propanedinitrile] (ITIC) as the acceptor exhibited higher power conversion efficiencies (>8.0%) for the same device configuration. In addition, the 3MTB‐ and 3MTT‐based PSC devices displayed excellent shelf‐life even after aging for over 1000 h. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1528–1535

Perylene Diimide-Based Zwitterion as the Cathode Interlayer for High-Performance Nonfullerene Polymer Solar Cells.

Nonfullerene polymer solar cells (PSCs) have earned widespread and intense interest on account of their properties such as tunable energy levels, potential for low-cost production processes, reduced energy losses, and strong light absorption coefficients. Here, a water-/alcohol-soluble zwitterion perylene diimide zwitterion (PDI-z) consisted of sulfobetaine ion as a terminal substituent and PDI as a conjugated core was synthesized. PDI-z was employed as an electron-transport layer (ETL) for nonfullerene PSC devices, obtaining an optimal power conversion efficiency (PCE) above 11.23%. Moreover, nonfullerene PSCs with the PDI-z cathode interlayer displayed an excellent performance on a large scale of interlayer thickness, which was compatible with printing fabrication techniques. Additionally, the PDI-z interlayer presented good ability of modifying high work function metals (for instance, Au, Cu, and Ag) in nonfullerene devices, and the Ag device displayed a PCE of 9.38%. This work provides a good alternative ETL for high-efficiency nonfullerene PSCs.

A narrow-bandgap donor polymer for highly efficient as-cast non-fullerene polymer solar cells with a high open circuit voltage

A new narrow-bandgap copolymer PBFTT, based on 4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene (BDT-2F) as donor unit and octyl-3-fluorothieno[3,4-b]thiophene-2-carboxylate (TT) as acceptor unit, was synthesized as donor material for non-fullerene (NF) polymer solar cells (PSCs) application. Compared to the analogue polymer PTB7-Th, PBFTT with two fluorine atoms in the conjugated side chains of BDT possesses a deeper HOMO energy level of −5.47 eV and a slightly enhanced hole mobility of 3.13 × 10−3 cm2 V-1 s-1 versus (vs.) a HOMO energy level of −5.30 eV and a hole mobility of 1.11 × 10−3 cm2 V-1 s-1 for PTB7-Th. Hence, the corresponding PSCs based on PBFTT:ITIC exhibited an optimal PCE of 9.1% with a Voc of 0.94 V, a Jsc of 16.0 mA cm−2, and a FF of 60.5% compared to a PCE of 6.8% with a Voc of 0.81 V, a Jsc of 14.2 mA cm−2 and a FF of 59.1% for PTB7-Th:ITIC-based PSCs. Notably, this PCE is among the highest values for the NF-PSCs based on narrow-bandgap polymer without extra treatments. These results indicate that PBFTT is a promising narrow-bandgap polymer donor material for NF-PSCs application.

Efficient Nonfullerene Polymer Solar Cells Enabled by Small‐Molecular Acceptors with a Decreased Fused‐Ring Core

AbstractTwo A1‐A2‐π‐D‐A2‐A1 structural small‐molecular acceptors with a decreased fused‐ring core, TIDT‐BT‐R2 and TIDT‐BT‐R6, are designed and synthesized by using thiophene‐indenothiophene (TIDT) as the core unit and benzothiadiazole‐rhodanine (BT‐R) as the end groups. The resulting small‐molecular acceptors exhibit the desirably complementary absorptions and well matched energy levels with the low‐bandgap donor copolymer of PTB7‐Th. Compared to TIDT‐BT‐R6, TIDT‐BT‐R2 with shorter side chains exhibits better crystallinity and higher charge carrier mobilities in its blend films. The nonfullerene solar cells (NFSCs) based on TIDT‐BT‐R2 also show higher exciton dissociation efficiency and lower charge recombination, which leads to higher Jsc and fill factor values. As a result, TIDT‐BT‐R2‐based NFSCs show a large Voc of 1.04 V and a high power conversion efficiency of 8.7% with a very low energy loss of 0.55 eV, which is one of the best values for PTB7‐Th‐based binary blend devices.

High-Performance Additive-/Post-Treatment-Free Nonfullerene Polymer Solar Cells via Tuning Molecular Weight of Conjugated Polymers.

In recent years, rapid advances are achieved in polymer solar cells (PSCs) using nonfullerene small molecular acceptors. However, no research disclosing the influence of molecular weight (Mn ) of conjugated polymer on the nonfullerene device performance is reported. In this work, a series of polymers with different Mn s are synthesized to systematically investigate the connection between Mn and performance of nonfullerene devices for the first time. It is found that the device performance improves substantially as the Mn increases from 12 to 38 kDa and a power conversion efficiency (PCE) as high as 10.5% is realized. It has to be noted this PCE is achieved without using any additives and post-treatments, which is among the top efficiencies of additive- and post-treatment-free PSCs. Most importantly, the variation trend of the optimal active layer thickness and morphology is significantly different from the device with fullerene as acceptor. The findings clarify the effect of Mn on the performance of nonfullerene PSCs, which would benefit further efficiency improvement of nonfullerene PSCs.

Small-molecule acceptors based on 4H-cyclopenta[1,2-b:5,4-b′]dithiophene units with near-infrared absorption for nonfullerene polymer solar cells

Two small-molecule acceptors 1CIC and 2CIC based on 4H-cyclopenta[1,2-b:5,4-b′]dithiophene units and 1,1-dicyanomethylene-3-indanone were developed. Compared with 1CIC, 2CIC possesses red-shift absorption, higher HOMO and LUMO energy levels, and higher electron mobility. Nonfullerene polymer solar cells based on PTB7-Th:2CIC gave a power conversion efficiency (PCE) of 3.53%, with an open-circuit voltage (Voc) of 0.75 V, a short-circuit current (Jsc) of 10.97 mA/cm2. As contrast, PTB7-Th:1CIC cell gave a PCE of 0.26%. Our results indicated that the absorption spectra of small-molecule acceptors containing indaceno[1,2-b:5,6-b′]dithiophene (IDT) core can be efficiently extended to near-infrared region by replacing the aromatic benzene ring of with 2,2′-bithiophene.

Improved performance of non-fullerene polymer solar cells using wide-bandgap random terpolymers

A series of wide-bandgap random terpolymers were designed and synthesized for application as the donor polymers in non-fullerene polymer solar cells. The benzodithiophene (BDT) derivatives with phenyl and thienyl conjugated side chains (denoted as BDTP and BDTT, respectively) were paired with an electron-withdrawing moiety (TzBI-O) to construct a series of wide-bandgap random terpolymers. The highest occupied molecular orbital energy levels of the resulting polymers gradually decreased from −5.26 to −5.33 eV upon increasing the BDTP content from 0 to 100%, leading to improved open-circuit voltages from 0.85 to 0.90 V for the resulting photovoltaic devices. In particular, photovoltaic devices based on terpolymers containing 50% BDTP exhibited the highest performance with a power conversion efficiency of 8.55%. This improvement was attributed to the suppressed bimolecular recombination and more balanced charge carrier mobilities in the terpolymer-based devices. These results demonstrate that the use of terpolymers represents a feasible strategy for the construction of highly efficient donors for non-fullerene polymer solar cells.

Wide Bandgap Molecular Acceptors with a Truxene Core for Efficient Nonfullerene Polymer Solar Cells: Linkage Position on Molecular Configuration and Photovoltaic Properties

AbstractTwo wide bandgap star‐shaped small molecular acceptors, para‐TrBRCN and meta‐TrBRCN, are synthesized for efficient nonfullerene polymer solar cells (PSCs). The tiny structural variation by just changing the linkage positions affects largely the inherent properties of the resulting molecules. Both molecules have a nonplanar 3D structure, which can prevent the excessively aggregation to realize the optimized morphology and ideal domain size in their active blends. Compared to para‐TrBRCN, meta‐TrBRCN exhibits the smaller distortions between the truxene skeleton and the benzothiadiazole units, which would also lead to the enhanced π–π stacking and charge transfer. When blending with PTB7‐Th, high power conversion efficiencies (PCEs) of 10.15% and 8.28% are obtained for meta‐TrBRCN and para‐TrBRCN devices, respectively. To make up the weak absorption of above binary active blend in the longer wavelength region and increase the whole device performance further, low bandgap 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone)‐5,5,11,11‐tetrakis(4‐hexylthienyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐dithiophene (ITIC‐Th) is added as the second acceptor material to fabricate ternary blend PSCs. After adding 20 wt% of ITIC‐Th, the resulting devices exhibit the well‐balanced optical absorption and fine‐tuned morphology, giving rise to the significantly improved PCE of 11.40% with much higher J sc of 18.25 mA cm−2 and fill factor of 70.2%.

Incorporating Trialkylsilylethynyl-Substituted Head-to-Head Bithiophene Unit into Copolymers for Efficient Non-Fullerene Organic Solar Cells.

Mediating the backbone coplanarity and solubility of oligothiophenes, especially the head-to-head (HH) disubstituted bithiophene, to achieve an optically and electronically advantageous building block for organic semiconductor materials is a vital yet challenging task. On the other hand, exploring polymer solar cells (PSCs) processed from nonhalogenated solvents is necessary toward their large-scale applications. In this contribution, we develop a HH-type bithiophene analogue (TIPS-T2) by strategically applying the triisopropylsilylethynyl (TIPS) scaffold as the side chain. TIPS can serve to narrow optical band gaps, lower the highest occupied molecular orbital level, reduce intrachain steric hindrance, and guarantee sufficient solubility of the involving polymers. Upon alternating with difluorobenzotriazole (FTAZ) or benzodithiophene-4,8-dione (BDD) acceptor units, two polymers named PT4Si-FTAZ and PT4Si-BDD are synthesized. Encouragingly, non-fullerene PSCs incorporating PT4Si-FTAZ yield a power conversion efficiency of 6.79% when processed from an environment-friendly solvent of trimethylbenzene because of its promoted backbone planarity, as demonstrated by density functional theory, higher hole mobility, and superior film morphology. The results indicate that TIPS-T2 is a promising building block for constructing photovoltaic polymers, and our findings offer an avenue for the ingenious use of TIPS as functional side chains.

Fine-tuning blend morphology via alkylthio side chain engineering towards high performance non-fullerene polymer solar cells

Two medium bandgap polymers (ffQx-TS1, ffQx-TS2) were designed and synthesized to investigate the influence of different alkylthio side chain on the morphology and photovoltaic performance of non-fullerene polymer solar cells (PSCs). Both polymers exhibit similar molecular weights and comparable the highest occupied molecular orbital (HOMO) energy level. However, the polymer with straight alkylthio chain delivers a root-mean-square (RMS) of 0.86 nm, which is slightly lower than that with branched chain (1.40 nm). The lower RMS benefits the ohmic contact between the active lay and interface layer, thus enhancedshortcircuitcurrent (Jsc) (from 13.54 mA cm−1 to 15.25 mA cm−1) could be obtained. Due to the enhancement of Jsc, better power conversion efficiency (PCE) of 7.69% for ffQx-TS2 could be realized. These results indicated that alkylthio side chain engineering is a promising method to improve photovoltaic performance.

Ternary Nonfullerene Polymer Solar Cells with a Power Conversion Efficiency of 11.6% by Inheriting the Advantages of Binary Cells

Ternary polymer solar cells (PSCs) were commonly fabricated with two donors or two acceptors; the third component has complementary absorption spectra with a host system to improve photon harvesting. In this work, a series of nonfullerene PSCs were fabricated with J71 as the donor and IT-M and/or ITIC with an almost identical band gap as acceptors. Although IT-M and ITIC have almost identical band gaps, the two optimized binary PSCs exhibit different photovoltaic parameters. The short current density (Jsc) and open-circuit voltage (Voc) of J71:IT-M based PSCs are larger than those of J71:ITIC based PSCs; the other key parameter, the fill factor (FF), is just the opposite. The power conversion efficiency (PCE) of optimized ternary PSCs arrives at 11.60% by inheriting the advantages of binary PSCs. This work may provide a new strategy for preparing efficient nonfullerene ternary PSCs by selecting binary PSCs with complementary photovoltaic parameters.

Synergistic effect of fluorination on both donor and acceptor materials for high performance non-fullerene polymer solar cells with 13.5% efficiency

A high performance polymer solar cells (PSCs) based on polymer donor PM6 containing fluorinated thienyl benzodithiophene unit and n -type organic semiconductor acceptor IT-4F containing fluorinated end-groups were developed. In addition to complementary absorption spectra ( 300–830 nm) with IT-4F, the PM6 also has a deep HOMO (the highest occupied molecular) level (−5.50 eV), which will lower the open-circuit voltage ( V oc) sacrifice and reduce the E loss of the IT-4F-based PSCs. Moreover, the strong crystallinity of PM6 is beneficial to form favorable blend morphology and hence to suppress recombination. As a result, in comparison with the PSCs based on a non-fluorinated D/A pair of PBDB-T:ITIC with a medium PCE of 11.2%, the PM6:IT-4F-based PSCs yielded an impressive PCE of 13.5% due to the synergistic effect of fluorination on both donor and acceptor, which is among the highest values recorded in the literatures for PSCs to date. Furthermore, a PCE of 12.2% was remained with the active layer thickness of up to 285 nm and a high PCE of 11.4% was also obtained with a large device area of 1 cm2. In addition, the devices also showed good storage, thermal and illumination stabilities with respect to the efficiency. These results indicate that fluorination is an effective strategy to improve the photovoltaic performance of materials, as well as the both fluorinated donor and acceptor pair-PM6:IT-4F is an ideal candidate for the large scale roll-to-roll production of efficient PSCs in the future.

Alkoxybenzothiadiazole-Based Fullerene and Nonfullerene Polymer Solar Cells with High Shunt Resistance for Indoor Photovoltaic Applications.

We synthesized three semicrystalline polymers (PTTBTBO, PDTBTBO, and P2FDTBTBO) by modulating the intra- and intermolecular noncovalent Coulombic interactions and investigated their photovoltaic characteristics under various light intensities. Low series (Rs) and high shunt (Rsh) resistances are essential prerequisites for good device properties under standard illumination (100 mW cm-2). Considering these factors, among three polymers, PDTBTBO polymer solar cells (PSCs) exhibited the most desirable characteristics, with peak power conversion efficiencies (PCE) of 7.52 and 9.60% by being blended with PC71BM under standard and dim light (2.5 mW cm-2), respectively. P2FDTBTBO PSCs exhibited a low PCE of 3.69% under standard light due to significant charge recombination with high Rs (9.42 Ω cm2). However, the PCE was remarkably improved by 2.3 times (8.33% PCE) under dim light, showing negligible decrease in open-circuit voltage and remarkable increase in fill factor, which is due to an exceptionally high Rsh of over 1000 kΩ cm2. Rs is less significant under dim light because the generated current is too small to cause noticeable Rs-induced voltage losses. Instead, high Rsh becomes more important to avoid leakage currents. This work provides important tips to further optimize PSCs for indoor applications with low-power electronic devices such as Internet of things sensors.