In order to induce greater light absorption, nano-patterning is often applied to the metal-oxide buffer layer in inverted bulk-heterojunction(BHJ) solar cells. However, current homogeneity was significantly disturbed at the interface, leading to an efficiency that was not fully optimized. In this work, an additional PC61BM layer was inserted between the ZnO ripple and the photoactive layer to enhance the electron extraction. The insertion of additional PC61BM layer provided substantial advantages in the operation of inverted BHJ solar cells; specifically, it enhanced current homogeneity and lowered accumulation and trapping of photogenerated charges at the ZnO interface. Inclusion of the additional PC61BM layer led to effective quenching of electron-hole recombination by a reduction in the number of accumulated charges at the surface of ZnO ripples. This resulted in a 16% increase in the efficiency of inverted BHJ solar cells to 7.7%, compared to solar cells without the additional PC61BM layer.

Indoor photovoltaics (IPVs) have great potential to provide a self‐sustaining power source for Internet‐of‐Things (IoT) devices. The rapid growth in demand for low‐power IoT devices for indoor application not only boosts the development of high‐performance IPVs, but also promotes the electronics and semiconductor industry for the design and development of ultra‐low‐power IoT systems. In this Review, the recent progress in IPV technologies, design rules, market trends, and future prospects for highly efficient indoor photovoltaics are discussed. Special attention is given to the progress and development of organic photovoltaics (OPVs), which demonstrate great possibilities for IPVs, owing to their bandgap tunability, high absorbance coefficient, semitransparency, solution processability, and easy large‐area manufacturing on flexible substrates. Highly efficient indoor organic photovoltaics (IOPVs) can be realized through designing efficient donor and acceptor absorber materials that have good spectral responses in the visible region and better energy‐aligned interfacial layers, and through modulation of optical properties. Interfacial engineering, photovoltage losses, device stability, and large‐area organic photovoltaic modules are surveyed to understand the mechanisms of efficient power conversion and challenges for IOPVs under indoor conditions as a self‐sustaining power source for IoT devices. Finally, the prospects for further improve in IOPV device performance and practical aspects of integrating IOPVs in low‐power IoT devices are discussed.

Using a novel polymer (polythienothiophene-co-benzodithiophenes 7 F-20) as a donor and phenyl-C₇₁-butyric acid methyl ester as an acceptor of bulk heterojunction, inverted organic photovoltaics (OPVs) were fabricated. Wet-chemically prepared ZnO and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) were used as buffer layers. Particularly, for PEDOT:PSS deposition, no annealing step was employed. This inverted OPV showed a power conversion efficiency (PCE) of ∼7.0%, which is comparable to the hitherto reported highest efficiency of the inverted OPV with vacuum-deposited MoO₃ as hole-collecting buffer layers without plasmonic enhancements. Incorporation of Au nanoparticles into PEDOT:PSS was performed for plasmonic enhancement of the electromagnetic field, whereas ZnO thin layers were deposited on ZnO using atomic layer deposition for quenching electron–hole recombination at surface defects of ZnO ripples. These additional treatments could be used for improving the performance of OPV, which ultimately resulted in a PCE of 7.9%.