# Overview on Different Types of Solar Cells: An Update
## 2 Organic Solar Cells
### Efficiency Highlights
The effect of the conformation of the additive is evaluated by using it with PBD-TF as the donor and either 2,2'- [[12,13-Bis(2-butyloctyl)-12,13-dihydro-3,9-dinonylbisthieno [2\",3\":4',5']thieno [2',3':4,5]pyrrolo [3,2-e:2',3'-g][1-3]benzothiadiazole-2,10-diyl]bis(methylidene(5,6-chloro-3-oxo-1H-indene-2,1(3H)-diylidene) ]bis[propanedinitrile] (BTP-eC9) or L8-BO as the acceptor material. In all cases, the performance properties improved compared with OSC without additive. However, planar-type SAD (SAD1) had the best performance, owing to its better insertion in the constituents of OSC. The best-performing device (PDBD-TF:L8-BO-SAD2) achieved \(\mathrm{V_{oc}}\), \(\mathrm{I_{sc}}\), FF, and PCE of 0.889 V, 26.73 mA/cm\({}^{2}\), 0.79, and 18.85%, respectively. Selectivity in the fabrication process can have a significant effect on the performance of OSC. A binary OSC device composed of Poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-chloro)thiophen-2-yl)-benzo [1,2-b:4,5-b']dithiophene))-alt-5,5'-(5,8-bis(4-(2-butyloctyl) thiophen-2-yl)dithieno [3',2':3,4,2\":3\":5,6]benzo [1,2-c][1,2,5]thiadiazole)] (D18) as the donor and L8-BO as the acceptor material is used for the evaluation of fabrication process [111]. Sequential deposition resulted in higher performance properties compared with blend heterojunction. OSCs prepared by blend casting had \(\mathrm{V_{oc}}\), \(\mathrm{I_{sc}}\), FF, and PCE of 0.911 V, 26.31 mA/cm\({}^{2}\), 0.76, and 18.14%, respectively, compared with 0.918 V, 26.86 mA/cm\({}^{2}\), 0.77, and 19.05% for the OSC prepared by sequential deposition. A combination of an asymmetric selenium-substituted pseudosymmetric electron acceptor, BS3 TSe-4F, and Y6 acceptors with D18 as the donor had a record high efficiency of OSC [112]. The fabricated device possessed \(\mathrm{V_{oc}}\), \(\mathrm{I_{sc}}\), FF, and PCE of 0.845 V, 29.41 mA/cm\({}^{2}\), 0.77, and 19.03%, respectively. Suppressing the charge recombination along with improving charge extraction are critically important for the performance of any OSC. [PERSON] and coworkers reported an improvement in the abovementioned properties by the combination of side-chain engineering of new nonfullerene acceptors (NFAs) in a ternary blend along with a volatilizable solid additive [113]. These hindrance of BTP-Th in molecular packing and phase separation is reduced by fluorination of side chains making BTP-FTh. The donor used in this case was Poly [[6,7-difluoro[(2-hexyladecyl)oxy]-5,8-quinoxalinediyl]-2,5-thiophenediyl] ] (PTQ10). An OSC composed of PTQ10 as the donor and binary blend of acceptor materials BTP-FTh:IDIC (0.8:0.2) along with dithione [3,2-b:2,3'-d]thiophene (DTT) as additive rendered V\({}_{\text{oc}}\), I\({}_{\text{sc}}\), FF, and PCE of 0.870 V, 27.17 mA/cm\({}^{2}\), 0.81, and 19.05%, respectively. Most recently, a record high PCE was reported by [PERSON] and coworkers for a tandem organic solar cell through the introduction of an interconnecting layer composed of electron-beam-evaporated TiO\({}_{\text{x}}\) and PEDOT:PSS [114]. The two sub-cells were PBDB-TF:GS-ISO/TiO\({}_{1.76}\) and TiO\({}_{1.76}\)/PEDOT:PSS, where an efficient electron extraction and low Schottky barriers were obtained due to control of O\({}_{2}\) flux during evaporation. For the first time, a PCE of more than 20% was obtained by any OSC. The archived V\({}_{\text{oc}}\), I\({}_{\text{sc}}\), FF, and PCE of the best device were 2.01 V, 13.14 mA/cm\({}^{2}\), 0.77, and 20.27%, respectively. The study opens a new era of 20% PCE in OSC technology.